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  • Calcium
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  • Springer  (246)
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  • Springer  (246)
  • MDPI Publishing
  • National Academy of Sciences
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  • 1
    Electronic Resource
    Electronic Resource
    Leucaena hedgerow intercropping and cattle manure application in the Ethiopian highlands III. Nutrient balances (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 204-211 
    Details
    ISSN: 1432-0789
    Keywords: Key words Alley cropping ; Calcium ; Magnesium ; Nitrogen ; Phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Balances between nutrients applied or mineralized and nutrients removed in maize grain and stover were calculated in a hedgerow intercropping experiment in which Leucaena leucocephala and L. pallida prunings and cattle manure were applied. Hedgerow intercropping (also called alley cropping) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. In control treatments, nutrient depletion per season was in the order of 7–19 kg N ha–1, 4–12 kg P ha–1, 10–26 kg K ha–1, 0–2 kg Ca ha–1 and 3–6 kg Mg ha–1. N fertilizer reversed the depletion of N, but it accelerated the depletion of the other nutrients. Manure and at least two applications of leucaena prunings resulted in net positive balances of N, K, and Ca between amounts applied or mineralized and amounts removed by maize. The amounts of P and Mg applied with, or mineralized from, prunings or manure were insufficient to offset the negative balances of these nutrients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050484
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  • 2
    Electronic Resource
    Electronic Resource
    Leucaena hedgerow intercropping and cattle manure application in the Ethiopian highlands I. Decomposition and nutrient release (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 182-195 
    Details
    ISSN: 1432-0789
    Keywords: Key words Alley cropping ; Calcium ; Magnesium ; Nitrogen ; Phosphorus ; Intercropping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  A litter bag technique was used to study the decomposition and release of N, P, K, Ca, and Mg from Leucaena leucocephala and L. pallida prunings and cattle manure in a hedgerow intercropping trial conducted in the Ethiopian highlands. Hedgerow intercropping (also called alley cropping or alley farming) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. Manure was the most resistant to decomposition, losing only 15% of its dry matter (DM) in 15 weeks, compared to 41–57% lost by leucaena prunings. Large quantities of K (up to 104 kg ha–1) were mineralized from prunings and manure, but Ca and Mg were mostly immobilized. More N and P were released from prunings than from manure, which resulted in net immobilization of these nutrients in the initial stages of decomposition and net mineralization in later stages. Between the leucaenas more N was mineralized and less Ca and Mg were immobilized when L. leucocephala prunings were applied than when L. pallida prunings were applied. Fertilizer N increased DM decomposition and N mineralization. Mineralization of the nutrients was constrained by lignin and polyphenol contents. It is concluded that leucaena mulch and cattle manure may be significant sources of N and K for crop growth, but external sources of P, Ca and Mg may be required, particularly in acid soils which have low contents of these nutrients. However, this fertility effect has to be evaluated against the competition effect of trees to predict crop response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050482
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  • 3
    Electronic Resource
    Electronic Resource
    Leucaena hedgerow intercropping and cattle manure application in the Ethiopian highlands II. Maize yields and nutrient uptake (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 196-203 
    Details
    ISSN: 1432-0789
    Keywords: Key words Alley cropping ; Calcium ; Magnesium ; Nitrogen ; Phosphorus ; Leaf pruning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The effects of Leucaena leucocephala and L. pallida prunings and cattle manure on maize nutrient uptake and yield were investigated in a hedgerow intercropping trial in the Ethiopian highlands. Hedgerow intercropping (also called alley cropping) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. For each leucaena species, the experiment had 16 treatments resulting from a factorial combination of four levels of leucaena leaf prunings (no prunings applied; first prunings applied; first and second prunings applied; first, second and third prunings applied), two levels of air-dried cattle manure (0 and 3 t dry matter ha–1) and two levels of N fertilizer (0 and 40 kg N ha–1 as urea). Uptake of N, P and K increased significantly with application of the three nutrient sources, but uptake of Ca and Mg either did not respond or decreased with application of prunings and manure. All the three factors increased maize grain and stover yields significantly, usually with no significant interactions between the factors. At least two applications of prunings were required to significantly increase nutrient uptake and maize yield. Maize in the row closest to the hedge did not respond to these nutrient inputs. It is concluded that hedgerow intercropping, with or without manure application, can increase crop yields moderately (to 2–3 t ha–1 maize grain yields) in the highlands, but P, Ca and Mg may have to be supplied from external sources if they are deficient in the soil. Additional N is still required for higher yields (〉4 t ha–1 maize grain yields). However, quantification of the competition effects of the trees is also required to confirm these results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050483
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  • 4
    Electronic Resource
    Electronic Resource
    On the mechanism of cesium-induced voltage and current tails in single ventricular myocytes (1999)
    Springer
    Journal of biomedical science 6 (1999), S. 161-175 
    Details
    ISSN: 1423-0127
    Keywords: Myocytes single ; Cesium ; Voltage and current tails ; Na-Ca exchange ; Calcium ; Cadmium ; Nickel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The mechanisms by which different concentrations of cesium modify membrane potentials and currents were investigated in guinea pig single ventricular myocytes. In a dose-dependent manner, cesium reversibly decreases the resting potential and action potential amplitude and duration, and induces a diastolic decaying voltage tail (Vex), which increases at more negative and reverses at less negative potentials. In voltage-clamped myocytes, Cs+ increases the holding current, increases the outward current at plateau levels while decreasing it at potentials closer to resting potential, induces an inward tail current (Iex) on return to resting potential and causes a negative shift of the threshold for the inward current. During depolarizing ramps, Cs+ decreases the outward current negative to inward rectification range, whereas it increases the current past that range. During repolarizing ramps, Cs+ shifts the threshold for removal of inward rectification negative slope to less negative values. Cs+-induced voltage and current tails are increased by repetitive activity, caffeine (5 mM) and high [Ca2+]o (8.1 mM), and are reduced by low Ca2+ (0.45 mM), Cd2+ (0.2 mM) and Ni2+ (2 mM). Ni2+ also abolishes the tail current that follows steps more positive than ECa. We conclude that Cs+ (1) decreases the resting potential by decreasing the outward current at more negative potentials, (2) shortens the action potential by increasing the outward current at potentials positive to the negative slope of inward rectification, and (3) induces diastolic tails through a Ca2+-dependent mechanism, which apparently is an enhanced electrogenic Na-Ca exchange.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02255900
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  • 5
    Electronic Resource
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    A biogeochemical study of the Podili and Tirupati area of Andhra Pradesh, India (1999)
    Springer
    Environmental geology 37 (1999), S. 313-316 
    Details
    ISSN: 1432-0495
    Keywords: Key words Biogeochemical study ; Dung ; Urine ; Milk ; Fluoride ; Grazing animals ; Podili ; Tirupati
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The fluoride content of dung, urine and milk of grazing animals, for example cow, she-buffalo, doe and ewe, was studied in the Podili area, India, (endemic fluorosis) and also in Tirupati (non-fluorosis) for the purpose of comparison. The data reveal that the fluoride content of the urine of animals is suitable for the preparation of biogeochemical atlases studying the environmental effect in relation to health.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002540050389
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  • 6
    Electronic Resource
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    Auxin augments conductance of K+ inward rectifier in maize coleoptile protoplasts (1999)
    Springer
    Planta 208 (1999), S. 38-45 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Auxin ; Calcium ; Coleoptile growth ; K+-inward rectifier (channel) ; pH ; Zea (coleoptile protoplasts)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Potassium is taken up by maize (Zea mays L.) coleoptile cells via a typical plant inward rectifier (K ir ). Sufficient conductance of this channel is essential in order to maintain auxin-stimulated cell elongation. It was therefore investigated whether the activity of this channel is subject to direct or indirect control by this growth hormone. Patch-clamp measurements of whole coleoptile protoplasts revealed no appreciable effect of externally applied 10 μM or 100 μM α-naphthaleneacetic acid (NAA) on the activity of K ir over test periods of ≥ 18 or ≥ 8 min, respectively. When, however, K ir was recorded in the cell-attached configiuration and 10 μM NAA administered to the bath medium, the conductance of K ir increased significantly in 13 out of 18 protoplasts over the control. This rise occurred at a fixed protoplast voltage after a lag period of less than 10 min and exhibited no voltage dependency. The absence of response to NAA of protoplasts in the whole-cell configuration indicates that auxin perception and channel control is linked via a soluble cytoplasmic factor and that this mediator is washed out or modified upon perfusion of the cytoplasm with pipette solution. To search for this expected diffusible factor the K ir current was recorded before and after elevation of Ca2+ and H+ in the cytoplasm. In the whole-cell configuration the increase in Ca2+ from a nanomolar value to 〉1 μM by means of Ca2+-release from the caged precursor Na2-DM-nitrophen left K ir unaffected. The whole-cell K ir conductance was also not affected upon addition of 10 mM Na+-acetate to the bath medium, an operation used to lower the cytoplasmic pH. This excludes a primary role for the known auxin-evoked rise in cytoplasmic Ca2+ and H+ in K ir activity. We postulate that another, as yet unknown, mechanism mediates the auxin-evoked stimulation of the number of active K ir channels in the plasma membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050532
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  • 7
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    Relocalization of the calcium gradient and a dihydropyridine receptor is involved in upward bending by bulging of Chara protonemata, but not in downward bending by bowing of Chara rhizoids (1999)
    Springer
    Planta 209 (1999), S. 414-423 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Chara (rhizoid ; protonema) ; Calcium ; Calcium channel ; Fluorescent-dihydropyridine ; Gravitropic tip growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The localization of cytoplasmic free calcium and a dihydropyridine (DHP) receptor, a putative calcium channel, was recorded during the opposite graviresponses of tip-growing Chara rhizoids and Chara protonemata by using the calcium indicator Calcium Crimson and a fluorescently labeled dihydropyridine (FL-DHP). In upward (negatively gravitropically) growing protonemata and downward (positively gravitropically) growing rhizoids, a steep Ca2+ gradient and DHP receptors were found to be symmetrically localized in the tip. However, the localization of the Ca2+ gradient and DHP receptors differed considerably during the gravitropic responses upon horizontal positioning of the two cell types. During the graviresponse of rhizoids, a continuous bowing downward by differential flank growth, the Ca2+ gradient and DHP receptors remained symmetrically localized in the tip at the centre of growth. However, after tilting protonemata into a horizontal position, there was a drastic displacement of the Ca2+ gradient and FL-DHP to the upper flank of the apical dome. This displacement occurred after the apical intrusion and sedimentation of the statoliths but clearly before the change in the growth direction became evident. In protonemata, the reorientation of the growth direction started with the appearence of a bulge on that site of the upper flank which was predicted by the asymmetrically displaced Ca2+ gradient. With the upward shift of the cell tip, which is suggested to result from a statolith-induced displacement of the growth centre, the Ca2+ gradient and DHP receptors became symmetrically relocalized in the apical dome. No major asymmetrical rearrangement was observed during the following phase of gravitropic curvature which is characterized by slower rates of bending. Labeling with FL-DHP was completely inhibited by a non-fluorescently labeled dihydropyridine. From these results it is suggested that FL-DHP labels calcium channels in rhizoids and protonemata. In rhizoids, positive gravitropic curvature is caused by differential growth limited to the opposite subapical flanks of the apical dome, a process which does not involve displacement of the growth centre, the calcium gradient or calcium channels. In protonemata, however, it is proposed that a statolith-induced asymmetrical relocalization of calcium channels and the Ca2+ gradient precedes, and might mediate, the rearrangement of the centre of growth, most likely by the displacement of the Spitzenkörper, to the upper flank, which results in the negative gravitropic reorientation of the growth direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050744
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  • 8
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    Commonalities between pollen/stigma and host/pathogen interactions: calcium accumulation during stigmatic penetration by Brassica oleracea pollen tubes (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 194-202 
    Details
    ISSN: 1432-2145
    Keywords: Key words.Brassica ; Calcium ; Epidermis ; Host/Pathogen ; Pollen/stigma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Parallels have been explored between the early stages of stigmatic penetration by pollen tubes and the infection of epidermal cells by fungal pathogens. In a striking resemblence to events following the infection of Hordeum sp. by Erysiphe graminis, X-ray microanalysis has revealed the accumulation of calcium at the stigmatic surface following pollinations in Brassica oleracea. X-ray mapping strongly indicates the calcium to be localised at the points at which either the pollen grain or its tube makes contact with the surface of the stigmatic papilla. No definitive measures were made of the concentration of calcium at these sites, but controls indicated the levels to be well in excess of those found in the cytosol. X-ray microanalysis at the pollen/stigma interface failed to detect the presence of silicon, an element frequently accumulated by epidermal cells in response to pathogenic challenge. The phenylpropanoid biosynthesis pathway is activated by many plant hosts following infection by fungal pathogens, and the accumulation of autofluorescent material in the stigma 24 h after contact with self pollen strongly indicates this pathway also to be activated after pollination. The timing of this response, however, suggests that phenolic products are unlikely to be involved in the rejection of self pollen. These data are discussed in the perspective of current views of defence systems present in angiosperm epidermal cells, and why these mechanisms fail to identify and reject incompatible pollen tubes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004970050192
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  • 9
    Electronic Resource
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    Changes of calcium distribution in ovules ofTorenia fournieri during pollination and fertilization (1999)
    Springer
    Protoplasma 208 (1999), S. 149-155 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Electron energy loss spectroscopy ; Embryo sac ; Torenia fournieri ; Fertilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Calcium distribution in ovules ofTorenia fournieri was studied by electron energy loss spectroscopy and transmission electron microscopic visualization of calcium antimonate precipitates. High calcium levels were found in the ovules ofT. fournieri. Calcium is situated mainly in extracellular regions before fertilization, including the surface of embryo sac, in the mucilage, and among the cells of the egg apparatus. Intracellular calcium was found only in the nucellar cells around the embryo sac and in the epidermis of the central axis and funiculus. After pollination, a labyrinthine structure (coralloid-like cell wall formation) develops on the micropylar surfaces of the egg apparatus that contain high levels of calcium. Calcium levels increase in the degenerating synergid after the penetration of the pollen tube. Calcium-antimonate precipitates are abundant in vacuoles of the disrupted synergid and pollen tube cytoplasm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279085
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  • 10
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    Cellulose and calcium lower the incidence of chemically-induced colon tumors in rats (1999)
    Springer
    Plant foods for human nutrition 54 (1999), S. 295-303 
    Details
    ISSN: 1573-9104
    Keywords: Calcium ; Cellulose ; Colon tumors ; Folic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In a 30-week preliminary study and a follow-up 22-week study (2 × 2 factorial), dimethylhydrazine (DMH)injections effectively induced colon tumors in Fischer-344rats. How this incidence of colon tumors might be affected by cellulose (preliminary study) or by calcium and folic acid (follow-up study) was examined. Cellulose in the dietappeared to provide some protection against DMH-induced colon tumors, but the protective effect of calcium was moreevident; normal levels of calcium (500 mg per 100 g diet), but not of folic acid (0.1 mg per 100 g diet), provided protection against colon tumors. The effect due to calciumwas observed whether viewed in terms of total number of tumors (p lt 0.01) or number of tumors per tumor-bearing rat(p 〈 0.01).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008149107282
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  • 11
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    Calcium and the regulation of mammalian ciliary beating (1999)
    Springer
    Protoplasma 206 (1999), S. 234-240 
    Details
    ISSN: 1615-6102
    Keywords: Cilia ; Calcium ; Acetylcholine ; Trachea ; Epithelium ; Video microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This report summarizes our recent work on the role of intracellular Ca2+ ([Ca2+]i) in regulating mammalian ciliary beat frequency (CBF). CBF from a single ovine cilium and [Ca2+]i from the same cell were measured by digital video phase contrast microscopy and fura-2 ratiometric imaging video microscopy, respectively. Cells were stimulated with two exposures to 10 μM acetylcholine (ACh). CBF was recorded during the first and [Ca2+]i during the second stimulation. ACh increased [Ca2+]i and CBF transiently with indistinguishable kinetics and, early in culture, even induced [Ca2+]i oscillations and ciliary frequency modulations with the same peak-to-peak time interval. Cells treated with 1 μM thapsigargin, an inhibitor of the endoplasmic-reticulum Ca2+-ATPase, showed transient [Ca2+]i and CBF increases, again with similar kinetics, which often remained at an elevated plateau. Application of ACh to cells pretreated with thapsigargin produced decreases in both [Ca2+]i and CBF. Finally, changing extracellular Ca2+-concentrations induced corresponding changes in [Ca2+]i that were associated with kinetically similar CBF changes. These data strongly suggested that [Ca2+]i is a critical signal to regulate CBF in mammalian tracheal epithelial cells. In an initial effort to provide constraints on the number and type of reactions that link changes in [Ca2+]i to changes in CBF, simultaneous recordings of both signals from a single cell were analyzed. Such recordings provided higher resolution of the kinetic responses of CBF and [Ca2+]i to ACh as well as they allowed direct assessment of the coupling between [Ca2+]i and CBF. Simultaneous measurements revealed that [Ca2+]i and CBF were perfectly correlated within the CBF measurement time resolution, except for the period of the fastest changes in both signals during the initial ACh exposure. There, changes in CBF lagged the changes in [Ca2+]i by 1–3 ciliary beat cycles (ca. 150–450 ms).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01288210
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  • 12
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    The intracellular events triggered by the self-incompatibility response inPapaver rhoeas (1999)
    Springer
    Protoplasma 208 (1999), S. 99-106 
    Details
    ISSN: 1615-6102
    Keywords: Papaver rhoeas ; Self-incompatibility ; Calcium ; Signal transduction ; Cell-cell recognition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In recent years self-incompatibility (SI) has come to be recognised as an important model system for studying cell-cell interactions and signalling in flowering plants. In this article we discuss the intracellular events associated with the SI response in the field poppy,Papaver rhoeas. The SI response inP. rhoeas is known to involve a Ca2+-based signalling pathway, activated following molecular interactions on the surface of incompatible pollen tubes. Evidence demonstrates that, following a transient increase in the concentration of cytosolic free Ca2+ ([Ca2+];) initiated by the SI response, phosphorylation of certain cytosolic proteins occurs, followed by activation of pollen gene expression. The magnitude of this transient Ca2+ wave and the localisation of cytosolic [Ca2+]i following the SI response are discussed. We also describe the character of the proteins specifically phosphorylated in the SI response and the nature of the protein kinases involved in their phosphorylation. Finally, we consider the possibility that the end result of the SI response inP. rhoeas may be analogous to programmed-cell-death mechanisms such as those seen in developmental processes and defence responses in various plant cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279079
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  • 13
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    Calcium, polarity and osmoregulation in Fucus embryos: one messenger, multiple messages (1998)
    Springer
    Experimental biology online 3 (1998), S. 1-14 
    Details
    ISSN: 1430-3418
    Keywords: Calcium ; Polarity ; Growth ; Signalling ; Cell volume control ; Fucus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This review addresses the role of cytosolic Ca2+in the regulation of embryonic polarity, polarised growth and osmotic control of cell volume with particular emphasis on the marine alga Fucus. Evidence is presented that the control of cell elongation in plants and algae requires the co-ordinate control of cell turgor and vesicle exocytosis, all of which are regulated by cytosolic Ca2+. In the Fucus embryo, polarised growth of the rhizoid cell requires sustained elevation of Ca2+ at the rhizoid apex whereas osmotic cell volume control is effected by transient elevations of cytosolic Ca2+. The mechanisms by which these signals are generated and their different downstream responses are discussed. Answers to questions of how specificity of signalling can be achieved by signal-response pathways which share common components will require more detailed knowledge of the interactions between different components and the spatial and temporal patterns of their activation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00898-998-0011-5
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  • 14
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    Aluminum and calcium distribution patterns in aluminum-intoxicated roots of Allium cepa do not support the calcium-displacement hypothesis and indicate signal-mediated inhibition of root growth (1998)
    Springer
    Planta 205 (1998), S. 175-180 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Allium ; Aluminum ; Calcium ; Root ; Rhizotoxicity ; Toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The aluminum and calcium distributions in the root tips of aluminum-intoxicated onions, Allium cepa L., were mapped using PIXE (particle-induced X-ray emission) microanalysis. Not enough aluminum was present to have replaced, atom-for-atom, more than a minor fraction of the calcium. Furthermore, no inverse relationship between variations in aluminum and calcium concentrations was observed for pairs of adjacent 30-μm-diameter regions. Our observations, therefore, do not support the hypothesis that aluminum substantially reduces the quantity of bound calcium by competing with calcium for binding sites. Instead we suggest that reductions in calcium content are a non-local and indirect consequence of aluminum-intoxication. We found that aluminum accumulates almost exclusively in a surface layer. Observations of wounded roots indicated that exposed internal tissue binds aluminum avidly, so we contend that the surface accumulation pattern indicates that little aluminum penetrates into the interior of the root. We argue that aluminum does not directly inhibit growth in the interior of the apical root meristem because root growth rate was unaffected by root cap removal which should greatly increase the aluminum concentration in the exposed interior region. We hypothesize that growth inhibition in the interior of the meristem is mediated by a signal initiated or disrupted by excess aluminum in the periphery of the meristem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050309
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  • 15
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    Association of nickel versus transport of cadmium and calcium in tonoplast vesicles of oat roots (1998)
    Springer
    Planta 204 (1998), S. 390-396 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Avena (root ; tonoplast) ; Calcium ; Cadmi‐um ; Nickel ; Tonoplast ; Transport (ion)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The plant vacuole has long been suspected of being a site for accumulation of Ni in plant roots, but testing this hypothesis directly by vacuole isolation is technically difficult and has not been reported. Here, we have attempted to determine if Ni can be transported into isolated oat (Avena sativa L.) root tonoplast vesicles as an alternative approach toward understanding the importance of the vacuole in Ni accumulation in roots. We found that, in contrast to Ca and Cd, Ni did not affect the proton gradient of vesicles (MgATP energized or artificially created), and further, that Cd/H antiport activity was not affected by the presence of Ni. Nickel was associated with vesicles, but relative rates of accumulation/association of metals with vesicles were Ca 〉 Cd  Ni. Protonophores and the potential Ni ligands citrate and histidine, and nucleoside triphosphates or PPi did not stimulate Ni association with vesicles. Comparison of Ni versus Ca and Cd associated with vesicles using various membrane perturbants indicated that while Ca and Cd are rapidly and principally antiported to the vesicle sap, Ni is only slowly associated with the membrane in a not-easily dissociated condition. Our results indicate the absence of an Ni/H antiport or Ni-nucleotide-dependent pump in oat root tonoplasts, and support the contention that the vacuole is not a major compartment for Ni accumulation in oat roots.
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    URL: http://dx.doi.org/10.1007/s004250050271
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  • 16
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    Blue light but not red light induces a calcium transient in the moss Physcomitrella patens (Hedw.) B., S. & G. (1998)
    Springer
    Planta 206 (1998), S. 278-283 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Aequorin ; Blue light ; Calcium ; Moss ; Photomorphogenesis ; Physcomitrella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. In caulonemal filaments of the moss, Physcomitrella patens, which had been incubated in darkness, 3 s irradiation with blue light (λmax 450 nm) at fluence rates of 100 μmol m−2 s−1 and above caused a transient␣increase in cytosolic calcium ion concentration, [Ca2+]cyt, which was both intensity- and time-dependent. Measurements of [Ca2+]cyt were made using moss transformed with the cDNA for apoaequorin and reconstituting the Ca2+-dependent photoprotein aequorin in the cytosol by incubation in coelenterazine.␣In response to blue light at fluence rates of 100–1000 μmol photons m−2 s−1, [Ca2+]cyt increased transiently from a basal level of approximately 50 nM to between 200 and 700 nM. Irradiation with red light did not evoke any measurable change in [Ca2+]cyt. The presence of calcium in the incubating medium was not required for the increase in [Ca2+]cyt to occur. A mutant strain, gad-139, was identified which required an irradiance of only 1 s to evoke a response. The kinetics showed a delay of approximately 6 s from the beginning of illumination before the beginning of the increase in [Ca2+]cyt. The data suggest that the activation of a photoreceptor rather than the direct opening of calcium channels is involved in this blue-light response.
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    URL: http://dx.doi.org/10.1007/s004250050401
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    Distribution of calmodulin protein and mRNA in growing pollen tubes (1998)
    Springer
    Sexual plant reproduction 11 (1998), S. 131-139 
    Details
    ISSN: 1432-2145
    Keywords: Key words Calmodulin ; mRNA ; Calcium ; Pollen tube ; Agapanthus umbellatus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Pollen tube growth is a vital process for angiosperm fertilisation and is dependent on the presence of a tip-focused gradient of cytosolic free calcium ([Ca2+]c). In order to clarify some of the target molecules which convey the Ca2+ signal information, we investigated calmodulin distribution during tube growth. Fluorescently labelled calmodulin was pressure microinjected into pollen tubes and its distribution monitored by confocal microscopy. Calmodulin distributes evenly throughout the cell, but some of its binding sites form a V-shaped collar behind the apical region. This specific association dissipates upon growth arrest, and suggests an interaction of calmodulin with cytoskeletal-bound target proteins. The distribution of calmodulin mRNA was also analysed by microinjection of fluorescently labelled mRNA. No specific pattern was observed, with an even localisation in the body of tube and a lower concentration in the cell apex. Studies with localised application of inhibitors/activators indicate that calmodulin plays a crucial role in tip elongation but does not direct tube orientation.
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    URL: http://dx.doi.org/10.1007/s004970050130
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    A calcium-dependent ergosterol mutant of Saccharomyces cerevisiae (1998)
    Springer
    Current genetics 34 (1998), S. 93-99 
    Details
    ISSN: 1432-0983
    Keywords: Key words Ergosterol ; Antifungal ; Calcium ; Fenpropimorph ; Azole ; ERG24 gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract ERG24 is the structural gene for the C14-sterol reductase in yeast. A lack of activity in that enzyme, mediated either by the morpholine fungicides or the insertional inactivation of ERG24, causes the accumulation of the aberrant sterol ignosterol. Cells producing this sterol are unable to grow aerobically in the routine laboratory medium, YPD. However, growth does occur on a synthetic defined medium. A novel calcium-dependent phenotype associated with alterations in the ergosterol biosynthetic pathway in yeast is described. In addition, reduction of yeast growth with an azole inhibitor of the C-14 sterol de-methylase was also modulated by an excess of calcium ions in the culture medium. These results define a new effect of ergosterol deficiency and provide important practical implications for utilizing morpholine and azole sterol biosynthetic-inhibiting fungicides.
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    URL: http://dx.doi.org/10.1007/s002940050371
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    Heat shock effects on second messenger systems of Neurospora crassa (1998)
    Springer
    Archives of microbiology 170 (1998), S. 191-200 
    Details
    ISSN: 1432-072X
    Keywords: Key words Heat shock ; Ethanol ; cAMP ; Protein ; kinase A ; cGMP ; Inositol phosphates ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Exposure of growing hyphae of Neurospora crassa to heat shock (44 °C) or ethanol (2.6 M) for 1 h induced a significant increase in the cAMP level, which reached a maximum approximately 2 min after the beginning of treatment and then decreased to control values despite continued heat or ethanol exposure. A 10-s heat shock or a 5-s ethanol shock also resulted in a transient cAMP increase 2 min after the pulse. Heat shock or ethanol treatment led to an increase in the amount of catalytic subunits of the cAMP-dependent protein kinase A in the nucleus almost synchronously with the increase of cAMP in the cytoplasm. The concentration of cGMP decreased a few seconds after the beginning of heat shock (44 °C) or ethanol treatment (2.6 M) to approximately 50% of the control level. Exposure to heat shock (44 °C, 1 h) led to an increase in the amount of inositol phosphates 0.5–2 min after the onset of heat shock. Thereafter, inositol phosphate levels dropped to control values despite continued heat exposure. Incubation of growing hyphae with cAMP or 8-Br-cAMP led to a two- to threefold increase of inositol phosphates 10–300 s after the beginning of incubation. Heat treatment furthermore caused a rapid release of calcium from vacuoles as determined by Fura-2 measurement of the calcium content released from isolated vacuoles. These heat-shock-dependent second messenger changes may play a role in the heat-shock-induced phase shifts of the circadian clock and heat-shock-induced conidiation.
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    URL: http://dx.doi.org/10.1007/s002030050633
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    Calcium distribution in fertile and sterile anthers of a photoperiod-sensitive genic male-sterile rice (1998)
    Springer
    Planta 204 (1998), S. 183-192 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Anther ; Calcium ; Male sterility ; Oryza (fertility) ; Pollen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Potassium antimonate was used to locate Ca2+ in fertile and sterile anthers of a photoperiod-sensitive genic male-sterile rice (Oryza sativa L. japonica). During the development of fertile anthers, abundant calcium precipitates accumulated in the anther walls and on the surface of pollen grains and Ubish bodies at the late developmental stage of the microspore, but not in the cytoplasm of pollen grains. Following the accumulation of starch grains in pollen, calcium precipitates on pollen walls diminished and increased in parenchymatous cells of the connective tissue. In sterile anthers, calcium precipitates were abundant in the middle layer and endothecium, but not in the tapetum, as was found in fertile anthers. A special cell wall was observed between the tapetum and middle layer of sterile anthers that appeared to relate to distinctive calcium accumulation patterns and poor pollen wall formation in the loculi. The formation of different patterns of antimonate-induced calcium precipitates in the anthers of photoperiod-sensitive genic male-sterile rice indicates that anomalies in the distribution of calcium accumulation correlate with the failure of pollen development and pollen abortion.
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    URL: http://dx.doi.org/10.1007/s004250050245
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    Sutural mineralization of rat calvaria characterized by atomic-force microscopy and transmission electron microscopy (1998)
    Springer
    Cell & tissue research 294 (1998), S. 93-97 
    Details
    ISSN: 1432-0878
    Keywords: Key words Calvaria ; Mineralization ; Calcium ; Phosphorus ; Apatite ; Atomic-force microscopy ; Transmission electron microscopy ; Rat (Sprague Dawley)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  The application of transmission electron microscopy (TEM) and atomic-force microscopy (AFM) aid the acquisition of detailed structural information on the process of hard tissue formation. The sutural mineralization of rat calvaria is taken as a model for a collagen-related mineralization system. After cryofixation or chemical fixation an anhydrous tissue preparation technique with no staining procedures is used. The atomic-force microscope and the transmission electron microscope are used for structural analysis of the mineralizing region of the sutural tissue. With the application of AFM the collagen macroperiod is shown to be well represented in the unmineralized sutural tissue. At the mineralization front the collagen fibrils are found to be thickened and to change to a characteristic stacked platelet structure. Using TEM the macroperiod is faintly visible before mineral crystallites have formed and is more prominent after the apatite crystallization has started in the fibrils. In this step a needle-like structure of the newly formed apatitic crystals is visible.
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    URL: http://dx.doi.org/10.1007/s004410051159
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    Apoptosis and redox homostasis: On a possible mechanism of action of Bcl-2 (1998)
    Springer
    Protoplasma 205 (1998), S. 10-20 
    Details
    ISSN: 1615-6102
    Keywords: Proto-oncogene product Bcl-2 ; Calcium ; Mitochondria ; Plasma membrane NADH oxidoreductase ; Transcription factor NF-κB
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We discuss the involvement of several mammalian redox systems in the regulation of apoptosis. We focus especially on the role that mitochondria and the still ill-characterized plasma membrane NADH-oxidoreductase system play in apoptosis. The latter system was shown to respond to downregulation of mitochondrial function; inhibition of either system induces apoptosis. Apoptosis induced by inhibitors of the oxidase involves both Bcl-2 and calcineurin, two proteins recently shown to be capable of forming a tight complex. We suggest that Bcl-2 acts as an antioxidant, but in an electron sense rather than in an oxygen sense.
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    URL: http://dx.doi.org/10.1007/BF01279288
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    Cytosolic Ca2+ and H+ buffers in green algae: A reply (1998)
    Springer
    Protoplasma 203 (1998), S. 210-213 
    Details
    ISSN: 1615-6102
    Keywords: Allosteric interaction ; Calcium ; Cytosolic buffer capacity ; Exchange buffer ; Eremosphaera viridis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The explanation of the coupling between butyrateinduced changes in cytosolic pH and pCa by means of a H+/Ca2+ exchange buffer as proposed by Plieth et al. [Protoplasma (1997) 198: 107–124; 199: 223] was questioned by Schönknecht and Bethmann [Protoplasma (1998) 203: 206–209]. They suggested an allosteric control of binding similar to the Hill equation. Fitting the measured pH-pCa coupling shows that a distinction between the models requires data which would be outside the experimentally accessible range. Plausibility considerations provide a support for the exchange buffer. The Hill equation is just a phenomenological approach which does not account for the diversity of allosteric mechanisms. The benefits of the exchanger model are firstly its mechanistic simplicity and secondly its flexibility as the same set of equations can also be used for an allosteric interaction between H+- and Ca2+-binding sites. The model can easily be extended to include future more detailed data. Finally, the cytosolic buffer capacities for H+ and Ca2+ are discussed.
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    Prevention and Treatment of Postmenopausal Osteoporosis (1998)
    Springer
    Pharmacy world & science 20 (1998), S. 198-205 
    Details
    ISSN: 1573-739X
    Keywords: Bisphosphonates ; Calcium ; Hormone Replacement Therapy ; Menopause ; Osteoporosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The purpose of the review is to outline the interventions, both pharmacological and non‐pharmacological, available to prevent postmenopausal osteoporosis (PMO) and treat the established disease. Current suggested guidelines for the most cost‐effective treatment and prophylactic strategies are included following a consideration of the available options. As life expectancy has increased so has the incidence of PMO which has major quality of life implications for the sufferers and economic implications for the authorities responsible for their treatment. PMO represents a significant public health problem and although more effective treatments are becoming available prevention of the disease by taking account of existing risk factors is preferable. Indeed, a population approach to prevention may be more cost effective than screening for the disease. Attention to dietary calcium intake and exercise regimes have been shown to be effective prophylactic measures premenopausally, while the treatment of choice is hormone replacement therapy (HRT). HRT treats other postmenopausal symptoms in addition to PMO and is available in many presentations, containing different hormones, at different doses intended for different routes of administration. The optimum treatment duration is controversial and may contribute to some of the risks associated with HRT such as endometrial and breast carcinoma and venous thromboembolism (VTE). Newer effective treatments include the bisphosphonates and novel formulations of calcitonin, but older approaches such as vitamin D, anabolic steroids and fluoride are still utilised in some circumstances. However, most promise has been shown by synthetic hormonal modulators currently being trialled.
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    URL: http://dx.doi.org/10.1023/A:1008682921480
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    Mitochondrial Ca2+ Transients in Cardiac Myocytes During the Excitation–Contraction Cycle: Effects of Pacing and Hormonal Stimulation (1998)
    Springer
    Journal of bioenergetics and biomembranes 30 (1998), S. 207-222 
    Details
    ISSN: 1573-6881
    Keywords: Calcium ; cardiac myocytes ; confocal microscopy ; Fluo 3 ; Indo 1 ; isoproterenol ; mitochondria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Using laser scanning confocal microscopy, our objective was to measure mitochondrial, nuclear, and cytosolic free ionized Ca2+ in adult rabbit cardiac myocytes loaded with Ca2+-indicating fluorophores. When myocytes were loaded with Fluo 3 at 37°C, the fluorophore was loaded extensively into the cytosol and nucleus, but poorly into mitochondria, and Fluo 3 fluorescence transients after field stimulation were confined to the cytosol and nucleus. In contrast, after loading at 4°C, Fluo 3 also entered mitochondria, and large transients of mitochondrial Fluo 3 fluorescence then occurred after stimulation. Isoproterenol (1 μM) increased the magnitude of Ca2+ transients and their subsequent rate of decay, an effect more marked in the cytosol and nucleus than in mitochondria. As pacing frequency was increased from 0.5 to 2 Hz, diastolic mitochondrial Ca2+ rose markedly in the absence but not in the presence of isoproterenol. Resting Ca2+ estimated by Indo 1 ratio imaging using UV/visible laser scanning confocal microscopy was about 200 nM in all compartments. During field stimulation, Ca2+ transiently increased to 671, 522, and 487 nM in cytosol, interfibrillar mitochondria, and perinuclear mitochondria, respectively. Isoproterenol increased these respective peak values to 1280, 750, and 573 nM. These results were consistent with those obtained in Fluo 3 experiments. We conclude that rapid mitochondrial Ca2+ transients occur during excitation–contraction coupling in adult rabbit cardiac myocytes, which may be important in matching mitochondrial metabolism to myocardial ATP demand during changes in cardiac output.
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    URL: http://dx.doi.org/10.1023/A:1020588618496
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    Pancreatic islets cultured on extracellular matrix: An excellent preparation for microfluorometry (1998)
    Springer
    Methods in cell science 19 (1998), S. 255-268 
    Details
    ISSN: 1573-0603
    Keywords: Calcium ; In vitro ; Insulin secretion ; Islets of Langerhans ; Metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have examined the use of extracellular matrix (ECM) as a substratum for mouse pancreatic islet cultures with special reference to microfluorometry work. We find the techniques for obtaining and maintaining ECM-producing cell cultures and coating of glass straightforward. The islets attached readily to ECM-coated glass and with time spread out. Cultures were probed for glucose responses after one day, one week and two weeks. Upon stimulation with 10 mM glucose, the well-established initial changes in [Ca2+]i, (monitored with Fura-2), as well as oscillations upon prolonged exposure, were observed. At 20 mM glucose only an elevated level without oscillations was seen. Similar responses were observed during the two weeks in culture. After one week in culture or more, single cell measurements of qualitative changes in [Ca2+]i and cell membranepotential (monitored with the dye bis-(1,3-dibutyl-barbituric acid) trimethine oxonol (DiBAC4(3)) could be performed concurrently on single cells at the islet periphery with ordinary fluorescence microscopy equipment. Simultaneous measurements of NAD(P)H and flavine adenine dinucleotide (FAD) fluorescence as well as measurements of rhodamine 123 fluorescence for mitochondrial membrane potential showed stable metabolic responses to glucose over the entire culture period. The islets had clearly elevated insulin secretion at 10 and 20 mM glucose compared to the secretion at 3 mM. In conclusion, mouse pancreatic islets cultured for up to two weeks on ECM-coated glass coverslips provide a functionally well- preserved and reproducible preparation for microfluorometry. The largest benefit of the method is that whole islet responses as well as single cell responses at the islet periphery can be monitored, using the same preparation.
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    URL: http://dx.doi.org/10.1023/A:1009712630494
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    Genetic variability and diversity for protein and calcium contents in finger millet (Eleusine coracana (L.) Gaertn) in relation to grain color (1998)
    Springer
    Plant foods for human nutrition 52 (1998), S. 353-364 
    Details
    ISSN: 1573-9104
    Keywords: Calcium ; Finger millet ; Genetic diversity ; Genetic variability ; Grain quality ; Protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Analysis of 36 genotypes of finger millet ( Eleusine coracana (L.) Gaertn) with varying seed colors revealed a wide range of protein and calcium contents. White seeded genotypes had higher protein contents, while brown seeded types had a wide range of values. The brown seeded genotype GE 2500 had the highest protein content. Although protein content had significant negative association with calcium content, white seeded types had moderate levels of calcium. The genotypic coefficients of variability were moderate and high for protein and calcium, respectively. High heritability coupled with high genetic advance indicated their governance by additive gene action. A negative significant correlation was observed between protein content and grain yield. Mahalanobis D 2 analysis grouped the 36 genotypes into eight clusters. Clustering pattern failed to indicate any relationship between genetic diversity and geographic diversity. Based on genetic diversity and performance, the genotypes MS 1168, MS 174 and CO 13 were found to be suitable for use as parents in a hybridization program for improving yield; the genotypes MS 1168, MS 174 and MS 2869 for protein and Malawi 1915 and CO 11 for calcium. Protein and calcium contents contributed less to genetic divergence.
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    URL: http://dx.doi.org/10.1023/A:1008074002390
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    Overdrive excitation in the guinea pig sinoatrial node superfused in high [K+]o (1997)
    Springer
    Journal of biomedical science 4 (1997), S. 179-191 
    Details
    ISSN: 1423-0127
    Keywords: Sinoatrial node ; High potassium ; Overdrive excitation ; Oscillatory afterpotential and prepotential ; Calcium ; Tetrodotoxin ; Sodium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The aim of the present experiments was to study the characteristics and mechanisms of the rhythm induced by overdrive (‘overdrive excitation’, ODE) in the sinoatrial node (SAN) superfused in high [K+]o (8–14 mM). It was found that: (1) overdrive may induce excitation in quiescent SAN and during a slow drive; (2) in spontaneously active SAN, overdrive may accelerate the spontaneous discharge; (3) immediately after the end of overdrive, a pause generally precedes the onset of the induced rhythm; (4) during the pause, an oscillatory potential (Vos) may be superimposed on the early diastolic depolarization (DD); (5) during the subsequent late DD, a different kind of oscillatory potential appears near the threshold for the upstroke (ThVos) which is responsible for the initiation of spontaneous activity; (6) once started, the induced rhythm is fastest soon after overdrive; (7) faster drives induce longer and faster spontaneous rhythms; (8) the induced action potentials are slow responses followed by DD with a superimposed Vos, but ThVos is responsible for ODE; (9) the induced rhythm subsides when ThVos miss the threshold and gradually decay; (10) low [Ca2+]o abolishes ODE; (11) in quiescent SAN, high [Ca2+]o induces spontaneous discharge through ThVos and increases its rate by enhancing Vos and shifting the threshold to more negative values, and (12) tetrodotoxin abolishes ODE as well as the spontaneous discharge induced by high [Ca2+]o. In conclusion, in K+-depolarized SAN, ODE may be present in the apparent absence of calcium overload, is Ca2+- and Na+-dependent and is mediated by ThVos and not by Vos.
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    Effects of calcium and magnesium on strontium distribution coefficients (1997)
    Springer
    Environmental geology 32 (1997), S. 219-229 
    Details
    ISSN: 1432-0495
    Keywords: Key words Strontium ; Calcium ; Magnesium ; Distribution ; Distribution coefficient ; Kd ; Competing cations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The effects of calcium and magnesium on the distribution of strontium between a surficial sediment and simulated wastewater solutions were measured as part of an investigation to determine strontium transport properties of surficial sediment at the Idaho National Engineering Laboratory (INEL), Idaho. The investigation was conducted by the U.S. Geological Survey and Idaho State University, in cooperation with the U.S. Department of Energy. Batch experimental techniques were used to determine strontium linear sorption isotherms and distribution coefficients (K d's) using simulated wastewater solutions prepared at pH 8.0±0.1 with variable concentrations of calcium and magnesium. Strontium linear sorption isotherm K d's ranged from 12±1 to 85±3 ml/g, increasing as the concentration of calcium and magnesium decreased. The concentration of sorbed strontium and the percentage of strontium retained by the sediment were correlated to aqueous concentrations of strontium, calcium, and magnesium. The effect of these cation concentrations on strontium sorption was quantified using multivariate least-squares regression techniques. Analysis of data from these experiments indicates that increased concentrations of calcium and magnesium in wastewater discharged to waste disposal ponds at the INEL increases the availability of strontium for transport beneath the ponds by decreasing strontium sorption to the surficial sediment.
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    Effects of xenon on intracellular Ca2% release in human endothelial cells (1997)
    Springer
    Experimental biology online 2 (1997), S. 1-17 
    Details
    ISSN: 1430-3418
    Keywords: Calcium ; Endothelium ; Xenon ; Anesthesia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Using human endothelial cells loaded with the Ca2% indicator Fura2 the effects of xenon on changes in intracellular Ca2% were studied. The basal level of intracellular Ca2% is not affected upon incubation of the cells in buffer saturated either with 100% xenon or with 70% xenon/30% air, a concentration which corresponds in humans to the minimum alveolar concentration necessary to induce anesthesia in 50% of patients. A defined cellular response such as the Ca2% change induced by application of adenosine triphosphate (ATP) makes it possible to study the signalling chain between the stimulus and the various forms of Ca2% response. ATP induces a typical Ca2% fingerprint composed of an internal Ca2% release consisting of several oscillations plus an additional Ca2%-induced Ca2% influx from the outside. The latter is absent in Ca2%-free medium. When cells are incubated with xenon, only the first part of the ATP-induced Ca2% response is found corresponding to the internal release of Ca2%; the subsequent Ca2%-induced Ca2% influx does not take place. If xenon is removed, a fast recovery is observed and the cells again show both parts of the Ca2+ response. Such selective inhibition of Ca2+-induced Ca2+ influx is not obtained when xenon is replaced by N2; the ATP response of the cell remains the same as that of untreated cells. Similar effects of xenon treatment can also be observed when the cells are treated with thapsigargin, a specific inhibitor of the SERCA systems. The Ca2+-induced Ca2+ release is almost completely suppressed in the presence of xenon. We conclude that xenon may act on the cellular level on defined sites of the mechanisms regulating the Ca2+-release-activated Ca2+ channels of the plasma membrane and that this property may be related to its anesthetic effect.
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    URL: http://dx.doi.org/10.1007/s00898-997-0003-x
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    Hydrogen fluoride effects on plasma membrane composition and ATPase activity in needles of white pine (Pinus strobus) seedlings pretreated with 12 h photoperiod (1997)
    Springer
    Trees 11 (1997), S. 248-253 
    Details
    ISSN: 0931-1890
    Keywords: Key words ATPase ; Fluoride ; Lipids ; Pine ; Plasma membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Eastern white pine (Pinus strobus L.) seedlings were pretreated with 12 h photoperiod to induce dormancy. Dormant plants were fumigated with 0.5 ppb (0.4 μg m–3) or 2.0 ppb (1.6 μg m–3) hydrogen fluoride (HF) for 2 – 28 days. Plasma membranes were isolated from needles of treated and control seedlings to determine their chemical composition and ATPase activity. For all analyses, only those plants which did not show needle necrosis were selected. The amount of plasma membrane phospholipid expressed on a plasma membrane protein basis was higher after 2 days in the 0.5 ppb HF treatment as compared to controls. After 2 days of 2.0 ppb HF treatment as well as after 8 and 28 days of both HF treatments phospholipid to protein ratios in fluoride treated seedlings were lower as compared to control levels. A decrease in sterol levels could be observed after 2 days in both HF treatments. A large increase in the ratio of sterols to proteins was observed in plasma membranes of eastern white pine seedlings treated with 0.5 ppb HF for 28 days. Increased sterol to phospholipid ratios were observed after 8 and 28 days in 0.5 ppb and after 2 and 8 days of 2.0 ppb HF treatment. A decrease in ATPase activity was observed after 8 days with both fluoride treatments. Drastic increase of ATPase activity was observed after 28 days of HF treated plants. Observed changes of sterol and phospholipid levels after only 2 days of fumigation suggest early fluoride effects on plasma membrane composition during plant dormancy.
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    URL: http://dx.doi.org/10.1007/PL00009671
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    Calcium distribution in fertilized and unfertilized ovules and embryo sacs of Nicotiana tabacum L. (1997)
    Springer
    Planta 202 (1997), S. 93-105 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Antimonate precipitation ; Calcium ; Embryo sac ; Fertilization ; Nicotiana (fertilization) ; Synergid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Potassium antimonate was used to localize Ca2+ in tobacco ovules from 0 to 7 d after anthesis in pollinated and emasculated flowers. Antimonate binds “loosely bound” Ca2+ into calcium antimonate; less-soluble forms are unavailable and free calcium usually escapes. Ovules are immature at anthesis. Abundant calcium precipitates in nucellar cells surrounding the micropylar canal. A difference between calcium in the two synergids emerges at 1 d, which is enhanced in pollinated flowers. The future receptive synergid accumulates more precipitates in the nucleus, cytoplasm and cell walls. After fertilization, micropyle precipitates diminish, and the ovule is unreceptive to further tube entry. In emasculated flowers 6 d after anthesis, ovular precipitates essentially disappear; however, flowers pollinated at 4–5 d and collected 2 d later largely restore their prior concentration of precipitates. Ovular precipitates occur initially in the nucellus, then the embryo sac, and finally the synergid and micropylar filiform apparatus. Possibility, calcium is released from the embryo sac, although no structural evidence of exudate formation was observed. Calcium precipitates in the ovule correlate with the ability of the ovule to be fertilized, suggesting that successful pollen tube entry and later development may require calcium of the class precipitated by antimonate.
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    Calcium-induced sperm fusion in Zea mays L. (1997)
    Springer
    Sexual plant reproduction 10 (1997), S. 74-82 
    Details
    ISSN: 1432-2145
    Keywords: Key words Zea mays ; Calcium ; Sperm fusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In this study, we examined morphological changes of isolated maize (Zea mays L.) sperm cells in the presence of Brewbaker and Kwack salts (BKS) or the individual components of BKS using light, transmission electron and scanning electron microscopy. Freshly isolated sperms are 7.5 μm in diameter. Treatment with BKS for 5 h resulted in large cells with a diameter up to 41 μm. Staining of sperm nuclei with 4′, 6-diamidino-2-phenylindole (DAPI) revealed two or more nuclei in a single cell, suggesting that BKS induces cell fusion. Treatment with each BKS component showed that cell fusion occurs only in the presence of calcium nitrate. Use of several calcium salts showed the same results, suggesting that the calcium ion, alone, is responsible for the observed cell fusion. Further studies were conducted to examine the relationship between calcium distribution and sperm location in pollen tubes using chlorotetracycline and DAPI. Growing maize pollen tubes exhibited a high membrane calcium region within 20–50 μm from the tip. The Sperms are found no closer than 90 μm to the tip of the tube, suggesting that sperms are located in a low calcium region prior to being released to the degenerating synergid.
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    URL: http://dx.doi.org/10.1007/s004970050070
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    The Role of Reactive Oxygen Species in Mitochondrial Permeability Transition (1997)
    Springer
    Bioscience reports 17 (1997), S. 43-52 
    Details
    ISSN: 1573-4935
    Keywords: Calcium ; cyclosporin A ; lipid peroxidation ; mitochondria ; mitochondrial membrane permeability transition ; protein oxidation ; reactive oxygen species
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract We have provided evidence that mitochondrial membrane permeability transition induced by inorganic phosphate, uncouplers or prooxidants such as t-butyl hydroperoxide and diamide is caused by a Ca2+-stimulated production of reactive oxygen species (ROS) by the respiratory chain, at the level of the coenzyme Q. The ROS attack to membrane protein thiols produces cross-linkage reactions, that may open membrane pores upon Ca2+ binding. Studies with submitochondrial particles have demonstrated that the binding of Ca2+ to these particles (possibly to cardiolipin) induces lipid lateral phase separation detected by electron paramagnetic resonance experiments exploying stearic acids spin labels. This condition leads to a disorganization of respiratory chain components, favoring ROS production and consequent protein and lipid oxidation.
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    URL: http://dx.doi.org/10.1023/A:1027335217774
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    Cellular specificity of the gravitropic motor response in roots (1997)
    Springer
    Planta 203 (1997), S. S115 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Arabidopsis ; Auxin ; Calcium ; Distal elongation zone ; Gravitropism (root) ; Zea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. A number of features of the gravitropic response of roots are not readily accounted for by the classical Cholodny-Went theory. These include the observations that (i) in the later stages of the response the growth gradient is reversed with no evident reversal of the auxin gradient; (ii) a major component of the acceleration of growth along the upper side occurs in the distal elongation zone (DEZ), a group of cells located between the meristem and the main elongation, not within the central elongation zone; and (iii) the initiation of differential growth in the DEZ appears to be independent of the establishment of auxin asymmetry. Alternative candidates for mediation of differential growth in the DEZ include calcium ions and protons. Gravi-induced curvature is accompanied by polar movement of calcium toward the lower side of the maize root tip and the DEZ is shown to be particularly sensitive to growth inhibition by calcium. Also, gravistimulation of maize roots causes enhanced acid efflux from the upper side of the DEZ. Evidence for gravi-induced modification of ion movements in the root tip includes changes in intracellular potentials and current flow. It is clear that there is more than one motor region in the root with regard to gravitropic responses and there is evidence that the DEZ itself consists of more than one class of responding cells. In order to gain a more complete understanding of the mechanism of gravitropic curvature, the physiological properties of the sub-zones of the root apex need to be thoroughly characterized with regard to their sensitivity to hormones, calcium, acid pH and electrical perturbations.
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    Plant responses to environmental stress: regulation and functions of the ArabidopsisTCH genes (1997)
    Springer
    Planta 203 (1997), S. S35 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Arabidopsis ; Calcium ; Calmodulin ; Cell wall ; Gene regulation (TCH genes) ; Xyloglucan endotransglycosylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Expression of the ArabidopsisTCH genes is markedly upregulated in response to a variety of environmental stimuli including the seemingly innocuous stimulus of touch. Understanding the mechanism(s) and factors that control TCH gene regulation will shed light on the signaling pathways that enable plants to respond to environmental conditions. The TCH proteins include calmodulin, calmodulin-related proteins and a xyloglucan endotransglycosylase. Expression analyses and localization of protein accumulation indicates that the potential sites of TCH protein function include expanding cells and tissues under mechanical strain. We hypothesize that at least a subset of the TCH proteins may collaborate in cell wall biogenesis.
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    URL: http://dx.doi.org/10.1007/PL00008113
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    Micro-heterogeneity of pectins and calcium distribution in the epidermal and cortical parenchyma cell walls of flax hypocotyl (1997)
    Springer
    Protoplasma 198 (1997), S. 9-19 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Demethylation ; Epidermal wall ; Polygalacturonate ; Polygalacturonic acid-Ca2+ conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Pectic polysaccharides are major components of the plant cell wall matrix and are known to perform many important functions for the plant. In the course of our studies on the putative role of pectic polysaccharides in the control of cell elongation, we have examined the distribution of polygalacturonans in the epidermal and cortical parenchyma cell walls of flax seedling hypocotyls. Pectic components have been detected with (1) the nickel (Ni2+) staining method to visualize polygalacturonates, (2) monoclonal antibodies specific to low (JIM5) and highly methylesterified (JIM7) pectins and (3) a combination of subtractive treatment and PATAg (periodic acid-thiocarbohydrazide-silver proteinate) staining. In parallel, calcium (Ca2+) distribution has been imaged using SIMS microscopy (secondary ion mass spectrometry) on cryo-prepared samples and TEM (transmission electron microscopy) after precipitation of calcium with potassium pyroantimonate. Our results show that, at the tissular level, polygalacturonans are mainly located in the epidermal cell walls, as revealed by the Ni2+ staining and immunofluorescence microscopy with JIM5 and JIM7 antibodies. In parallel, Ca2+ distribution points to a higher content of this cation in the epidermal walls compared to cortical parenchyma walls. At the ultrastructural level, immunogold labeling with JIM5 and JIM7 antibodies shows a differential distribution of pectic polysaccharides within cell walls of both tissues. The acidic polygalacturonans (recognized by JIM5) held through calcium bridges are mainly found in the outer part of the external wall of epidermal cells. In contrast, the labeling of methylesterified pectins with JIM7 is slightly higher in the inner part than in the outer part of the wall. In the cortical parenchyma cells, acidic pectins are restricted to the cell junctions and the wall areas in contact with the air-spaces, whereas methylesterified pectins are evenly distributed all over the wall. In addition, the pyroantimonate precipitation method reveals a clear difference in the Ca2+ distribution in the epidermal wall, suggesting that this cation is more tightly bound to acidic pectins in the outer part than in the inner part of that wall. Our findings show that the distribution of pectic polysaccharides and the nature of their linkages differ not only between tissues, but also within a single wall of a given cell in flax hypocotyls. The differential distribution of pectins and Ca2+ in the external epidermal wall suggests a specific control of the demethylation of pectins and a central role for Ca2+ in this regulation.
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    URL: http://dx.doi.org/10.1007/BF01282126
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    Pectin immunolocalization and calcium visualization in differentiating derivatives from poplar cambium (1997)
    Springer
    Protoplasma 199 (1997), S. 151-160 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Cambium ; Ionic microscopy ; Immunolocalization ; Pectins ; Populus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Calcium distribution and pectin esterification patterns in the cambial zone of poplar branches were studied with ionic microscopy and immunological tools respectively. Dynamic changes correlating with cell growth and cell differentiation were observed both on the xylem and on the phloem sides. In expanding cell walls of xylem derivatives, unesterified pectins were restricted to cell junctions and middle lamellae, occasionally accompanied by calcium ions. In contrast, in differentiating and mature phloem cells, acidic pectins and Ca2+ were present all over the walls leading to early stiffening of the polysaccharide network. Significant labelling was detected with JIM5 antibodies in some dictyosomes suggesting exocytosis of low methylated polymers towards the cell walls. At cell junctions, unesterified pectins might originate from the activity of pectinmethylesterases localized in these areas. Thus un- and deesterified pectins might be located in different cell wall domains whose distribution, varying with cell type, will confer specific extensibility to the wall matrix.
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    Photoreceptor Guanylate Cyclases: A Review (1997)
    Springer
    Bioscience reports 17 (1997), S. 429-473 
    Details
    ISSN: 1573-4935
    Keywords: Calcium ; guanylate cyclase ; photoreceptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Almost three decades of research in the field of photoreceptor guanylate cyclases are discussed in this review. Primarily, it focuses on the members of membrane-bound guanylate cyclases found in the outer segments of vertebrate rods. These cyclases represent a new guanylate cyclase subfamily, termed ROS-GC, which distinguishes itself from the peptide receptor guanylate cyclase family that it is not extracellularly regulated. It is regulated, instead, by the intracellularly-generated Ca2+ signals. A remarkable feature of this regulation is that ROS-GC is a transduction switch for both the low and high Ca2+ signals. The low Ca2+ signal transduction pathway is linked to phototransduction, but the physiological relevance of the high Ca2+ signal transduction pathway is not yet clear; it may be linked to neuronal synaptic activity. The review is divided into eight sections. In Section I, the field of guanylate cyclase is introduced and the scope of the review is briefly explained; Section II covers a brief history of the investigations and ideas surrounding the discovery of rod guanylate cyclase. The first five subsections of Section III review the experimental efforts to quantify the guanylate cyclase activity of rods, including in vitro and in situ biochemistry, and also the work done since 1988 in which guanylate cyclase activity has been determined. In the remaining three subsections an analytical evaluation of the Ca2+ modulation of the rod guanylate cyclase activity related to phototransduction is presented. Section IV deals with the issues of a biochemical nature: isolation and purification, subcellular localization and functional properties of rod guanylate cyclase. Section V summarizes work on the cloning of the guanylate cyclases, analysis of their primary structures, and determination of their location with in situ hybridization. Section VI summarizes studies on the regulation of guanylate cyclases, with a focus on guanylate cyclases activating proteins. In Section VII, the evidence about the localization and functional role of guanylate cyclases in other retinal cells, especially in “on-bipolar” cells, in which guanylate cyclase most likely plays a critical role in electrical signaling, is discussed. The review concludes with Section VIII, with remarks about the future directions of research on retinal guanylate cyclases.
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    SUR1 (CSG1 / BCL21), a gene necessary for growth of Saccharomyces cerevisiae in the presence of high Ca2+ concentrations at 37° C, is required for mannosylation of inositolphosphorylceramide (1997)
    Springer
    Molecular genetics and genomics 255 (1997), S. 570-579 
    Details
    ISSN: 1617-4623
    Keywords: Key words Saccharomyces cerevisiae ; Calcium ; Copper ; Sphingolipid ; CSG1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Saccharomyces cerevisiae cells require two genes, CSG1/SUR1 and CSG2, for growth in 50 mM Ca2+, but not 50 mM Sr2+. CSG2 was previously shown to be required for the mannosylation of inositol-phosphorylceramide (IPC) to form mannosylinositolphosphorylceramide (MIPC). Here we demonstrate that SUR1/CSG1 is both genetically and biochemically related to CSG2. Like CSG2, SUR1/CSG1 is required for IPC mannosylation. A 93–amino acid stretch of Csg1p shows 29% identity with the α-1, 6-mannosyltransferase encoded by OCH1. The SUR1/CSG1 gene is a dose-dependent suppressor of the Ca2+-sensitive phenotype of the csg2 mutant, but overexpression of CSG2 does not suppress the Ca2+ sensitivity of the csg1 mutant. The csg1 and csg2 mutants display normal growth in YPD, indicating that mannosylation of sphingolipids is not essential. Increased osmolarity of the growth medium increases the Ca2+ tolerance of csg1 and csg2 mutant cells, suggesting that altered cell wall synthesis causes Ca2+-induced death. Hydroxylation of IPC-C to form IPC-D requires CCC2, a gene encoding an intracellular Cu2+ transporter. Increased expression of CCC2 or increased Cu2+ concentration in the growth medium enhances the Ca2+ tolerance of csg1 mutants, suggesting that accumulation of IPC-C renders csg1 cells Ca2+ sensitive.
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    Milk composition and lactational output in the greater spear-nosed bat, Phyllostomus hastatus (1997)
    Springer
    Journal of comparative physiology 167 (1997), S. 389-398 
    Details
    ISSN: 1432-136X
    Keywords: Key words Milk composition ; Lactation ; Calcium ; Bats ; Phyllostomatidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Growth rates of mammalian young are closely linked to the ability of the mother to provide nutrients; thus, milk composition and yield provide a direct measure of maternal investment during lactation in many mammals. We studied changes in milk composition and output throughout lactation in a free-ranging population of the omnivorous bat, Phyllostomus hastatus. Fat and dry matter of milk increased from 9 to 21% and from 21 to 35% of wet mass, respectively, throughout lactation. Energy increased from 6 to 9 kJ · g−1 wet mass, primarily due to the increase in fat concentration. Total sugar levels decreased slightly but non-significantly. Mean sugar level was 4.0% of wet mass. Protein concentration increased from 6 to 11% of wet mass at peak lactation and then decreased as pups approached weaning age. Total milk energy output until pups began to forage was 3609 kJ. Milk levels of Mg, Fe, Ca, K, and Na averaged 0.55 ± 0.26, 0.23 ± 0.2, 8.75 ± 4.17, 5.42 ± 2.11, and 9.87 ± 4.3 mg · g−1 dry matter, respectively. Of the minerals studied, calcium appears to be most limiting in this species. The high degree of variability in foraging time, milk composition and milk yield between individuals at the same stage of lactation could potentially yield high variance in reproductive success among females of this polygynous species.
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    URL: http://dx.doi.org/10.1007/s003600050088
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    The plasma membrane calcium pump: Recent developments and future perspectives (1996)
    Springer
    Cellular and molecular life sciences 52 (1996), S. 1091-1100 
    Details
    ISSN: 1420-9071
    Keywords: Calcium ; ATPase ; calmodulin ; ion pumps
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The Ca2+ pump of the plasma membrane (PMCA) is regulated by a number of agents. The most important is calmodulin (CaM), which binds to a domain located in the C-terminal portion of the pump, removing it from an autoinhibitory site next to the active site. The CaM-binding domain is preceded by an acidic sequence which contains a hidden signal for endoplasmic reticulum (ER) retention. Chimeras of the PMCA and endoplasmic reticulum (SERCA) pumps have revealed the presence of a strong signal for ER retention in the first 45 residues of the SERCA pump. Four gene products of the PMCA pump are known: two of them (1 and 4) are ubiquitously expressed, two (2 and 3) are specific for nerve cells and may be induced by their activation. Mutagenesis work has identified four residues in three of the transmembrane domains of the pump which may be components of the trans-protein Ca2+ path. The mutation of two of these residues alters the membrane targeting of the pump.
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    Effects of long-term open-air exposure to fluoride, nitrogen compounds and SO2 on visible symptoms, pollutant accumulation and ultrastructure of Scots pine and Norway spruce seedlings (1996)
    Springer
    Trees 10 (1996), S. 157-171 
    Details
    ISSN: 1432-2285
    Keywords: Conifer ; Fluoride ; Nitrogen ; Sulphur dioxide ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Effects of SO2, aqueous fluoride (NaF) and a solution of nitrogen compounds (NH4NO3) on the visible symptoms, pollutant accumulation and ultrastructure of Scots pine (Pinus sylvestris L.) and Norway spruce [Picea abies (L.) Karst.] seedlings were studied in an open-air experiment lasting for 3 consecutive years. Visible injury symptoms were most pronounced in combination exposures and whenever F was applied. Visible symptoms correlated well with needle pollutant concentrations. Exposure to NaF increased needle F contents particularly when F was applied with SO2 or NH4NO3. This suggests that a reduction in N or SO2 emissions, in F polluted areas, could improve the condition of conifers via decreased accumulation of phytotoxic F in the needles. Norway spruce needles accumulated 2–10 times as much S and F as those of Scots pine. Microscopic observations showed various changes in the needle mesophyll cell ultrastructure. In both species, exposure to SO2 increased significantly the amount of cytoplasmic vacuoles, suggesting detoxification of excess sulphate or low pH. F treatments resulted in a significant enlargement of plastoglobuli in Scots pine and a darkening of plastoglobuli in Norway spruce. All exposures enhanced the accumulation of lipid bodies. An increased portion of translucent plastoglobuli was most pronounced in N treatments. Many of the ultrastructural changes and visible symptoms appeared only as number of years exposed increased, indicating that long-term experiments are needed. Both visible symptoms and ultrastructural changes pointed to the more pronounced sensitivity of Norway spruce compared to Scots pine. Ultrastructural results mostly supported earlier qualitative observations of F, N and SO2 effects on needle mesophyll cell ultrastructure. However, no reduction of thylakoids in SO2 containing exposure or curling of thylakoids in F exposure could be detected in the present study.
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    URL: http://dx.doi.org/10.1007/BF02340767
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    Effects of long-term open-air exposure to fluoride, nitrogen compounds and SO2 on visible symptoms, pollutant accumulation and ultrastructure of Scots pine and Norway spruce seedlings (1996)
    Springer
    Trees 10 (1996), S. 157-171 
    Details
    ISSN: 0931-1890
    Keywords: Key words Conifer ; Fluoride ; Nitrogen ; Sulphur dioxide ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Effects of SO2, aqueous fluoride (NaF) and a solution of nitrogen compounds (NH4NO3) on the visible symptoms, pollutant accumulation and ultrastructure of Scots pine (Pinus sylvestris L.) and Norway spruce [Picea abies (L.) Karst.] seedlings were studied in an open-air experiment lasting for 3 consecutive years. Visible injury symptoms were most pronounced in combination exposures and whenever F was applied. Visible symptoms correlated well with needle pollutant concentrations. Exposure to NaF increased needle F contents particularly when F was applied with SO2 or NH4NO3. This suggests that a reduction in N or SO2 emissions, in F polluted areas, could improve the condition of conifers via decreased accumulation of phytotoxic F in the needles. Norway spruce needles accumulated 2 – 10 times as much S and F as those of Scots pine. Microscopic observations showed various changes in the needle mesophyll cell ultrastructure. In both species, exposure to SO2 increased significantly the amount of cytoplasmic vacuoles, suggesting detoxification of excess sulphate or low pH. F treatments resulted in a significant enlargement of plastoglobuli in Scots pine and a darkening of plastoglobuli in Norway spruce. All exposures enhanced the accumulation of lipid bodies. An increased portion of translucent plastoglobuli was most pronounced in N treatments. Many of the ultrastructural changes and visible symptoms appeared only as number of years exposed increased, indicating that long-term experiments are needed. Both visible symptoms and ultrastructural changes pointed to the more pronounced sensitivity of Norway spruce compared to Scots pine. Ultrastructural results mostly supported earlier qualitative observations of F, N and SO2 effects on needle mesophyll cell ultrastructure. However, no reduction of thylakoids in SO2 containing exposure or curling of thylakoids in F exposure could be detected in the present study.
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    Cell signaling and heat shock protein expression (1996)
    Springer
    Journal of biomedical science 3 (1996), S. 379-388 
    Details
    ISSN: 1423-0127
    Keywords: Heat shock ; Calcium ; Sodium ; Inositol 1,4,5-trisphosphate ; Heat shock protein 70 kd ; Intracellular pH ; Protection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Exposure of cells and organs to heat shock is associated with numerous changes in various cellular metabolic parameters and overexpression of proteins collectively known as heat shock proteins (HSP). In this communication we review the cell-signaling events that are altered in response to heat shock as they relate to the subsequent induction of HSP 70 kd (HSP-70) expression. We also review the mechanisms by which HSP-70 is involved in conferring cytoprotective effects. The possibility of altering HSP expression through manipulations of the cell-signal process has clinical importance.
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    Decline in snail abundance due to soil acidification causes eggshell defects in forest passerines (1996)
    Springer
    Oecologia 105 (1996), S. 351-360 
    Details
    ISSN: 1432-1939
    Keywords: Snails ; Calcium ; Eggshell ; Avian reproduction ; Acidification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract On poor soils in the Netherlands an increasing number of great tits, Parus major, and of other forest passerines produce eggs with defective shells and have low reproductive success as a result of calcium deficiency. A similar increase in eggshell defects has been observed in Germany and Sweden. Snail shells are the main calcium source for tits in forests where defective eggshells do not occur, but are very little taken in forests where tits often have eggshell defects. We investigated whether a decrease in snail abundance on poor soils could be responsible for the decline in eggshell quality, and if so, what caused this decrease. Snail density in forests where tits have eggshell defects was much lower than in forests where tits do not have such defects. Snail density correlated with the calcium content and to a lesser extent with pH of the litter layer. Liming of a calciumpoor forest soil with few snails resulted in snail densities comparable to those on calcium-rich soils after 4 years. Snail density has declined on calcium-poor soils over the last two decades, but not on calcium-rich soils. Acid deposition has caused a decline of soil calcium on poor soils. We conclude, therefore, that anthropogenic acidification has caused a decline in snail populations, resulting in an increase in eggshell defects in birds in forests on poor soils.
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    Calcium pools, calcium entry, and cell growth (1996)
    Springer
    Bioscience reports 16 (1996), S. 139-157 
    Details
    ISSN: 1573-4935
    Keywords: Calcium ; serca pump ; endoplasmic reticulum ; cell growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The Ca2+ pump and Ca2+ release functions of intracellular Ca2+ pools have been well characterized. However, the nature and identity of Ca2+ pools as well as the physiological implications of Ca2+levels within them, have remained elusive. Ca2+ pools appear to be contained within the endoplasmic reticulum (ER); however, ER is a heterogeneous and widely distributed organelle, with numerous other functions than Ca2+ regulation. Studies described here center on trying to determine more about subcellular distribution of Ca2+ pools, the levels of Ca2+ within Ca2+ pools, and how these intraluminal Ca2+ levels may be physiologically related to ER function. Experiments utilizingin situ high resolution subcellular morphological analysis of ER loaded with ratiometric fluroescent Ca2+ dyes, indicate a wide distribution of inositol 1,4,5-trisphosphate (InsP3)-sensitive Ca2+ pools within cells, and large changes in the levels of Ca2+ within pools following InsP3-mediated Ca2+ release. Such changes in Ca2+ may be of great significance to the translation, translocation, and folding of proteins in ER, in particular with respect to the function of the now numerously described luminal Ca2+-sensitive chaperonin proteins. Studies have also focussed on the physiological role of pool Ca2+ changes with respect to cell growth. Emptying of pools using Ca2+ pump blockers can result in cells entering a stable quiescent G0-like growth state. After treatment with the irreversible pump blocker, thapsigargin, cells remain in this state until they are stimulated with essential fatty acids whereupon new pump protein is synthesized, functional Ca2+ pools return, and cells reenter the cell cycle. During the Ca2+ pool-depleted growth-arrested state, cells express a Ca2+ influx channel that is distinct from the store-operated Ca2+ influx channels activated after short-term depletion of Ca2+ pools. Overall, these studies indicate that significant changes in intraluminal ER Ca2+ do occur and that such changes appear linked to alteration of essential ER functions as well as to the cell cycle-state and the growth of cells.
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    Regulation of melatonin production and intracellular calcium concentrations in the trout pineal organ (1996)
    Springer
    Cell & tissue research 286 (1996), S. 315-323 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Pineal organ ; Melatonin ; Norepinephrine ; Calcium ; Fura-2 ; Photoreceptor ; Rainbow trout ; Oncorhynchus mykiss (Teleostei)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The present in vitro study correlates measurements of the melatonin production from trout pineal organs with those of the intracellular calcium concentration in pinealocytes. Melatonin production increases with decreasing irradiance and shows maximal values in darkness. Some pinealocytes exhibit spontaneous calcium oscillations, although most of them have a stable basal calcium concentration. Diminishing extracellular calcium and enhancing magnesium reduces melatonin release in the light-and dark-adapted state. The application of Co2+ decreases melatonin secretion in the mesopic and scotopic range, reversibly blocks spontaneous calcium oscillations, reduces the basal intracellular calcium concentration in non-oscillating pinealocytes, and inhibits the KCl-induced rise in intracellular calcium. Application of glutamate, norepinephrine, isoproterenol, or dopamine has no significant effect on melatonin secretion. Norepinephrine does not influence the calcium concentration in any of the trout pinealocytes. Treatment with the GABAA-receptor agonist muscimol causes a slight reduction of melatonin release in the mesopic and scotopic range of illumination, without affecting intracellular calcium concentrations. Thus, Co2+ and low calcium/high magnesium buffer reduce melatonin release through an action on the calcium concentration in trout pinealocytes and not through a blockade of synaptic transmission. All the data show that the trout pineal organ synthesizes and releases melatonin in relation to the irradiance of the incident light and that neuronal inputs have a minor, if any, influence on melatonin synthesis.
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    Effect of caffeine on cytosolic Ca2+ level and cytoplasmic streaming inNitella axilliformis (1996)
    Springer
    Protoplasma 190 (1996), S. 164-171 
    Details
    ISSN: 1615-6102
    Keywords: Caffeine ; Cytoplasmic streaming ; Calcium ; Nitella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effect of caffeine on cytosolic Ca2+ level and rate of cytoplasmic streaming was studied inNitella. External application of caffeine induced both a transient rise in cytosolic Ca2+ level and a decline in the rate of cytoplasmic streaming ofNitella. When EGTA-injected cells were bathed in EGTA-containing medium, external application of caffeine inhibited cytoplasmic streaming but induced no transient rise in cytosolic Ca2+ level. These results suggest that the inhibitory effect of caffeine on cytoplasmic streaming is independent of cytosolic Ca2+ level.
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    URL: http://dx.doi.org/10.1007/BF01281315
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    Lysosomotropic agents activate the capacity for calcium dependent pinocytosis in starvedAmoeba proteus: evidence for a mechanism involving phospholipase A2 (1996)
    Springer
    Protoplasma 192 (1996), S. 20-27 
    Details
    ISSN: 1615-6102
    Keywords: Amino acid ester ; Calcium ; Dantrolene ; Endocytosis ; Lysosome ; Phospholipase A2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Pinocytosis induced by Na+ was assayed by phase contrast microscopy in 8–12 days starvedAmoeba proteus. These cultures were inactive with respect to calcium-dependent Na+-induced pinocytosis, but treatment with amino acid methyl and ethyl esters increased their capacity for pinocytosis. Besides promoting pinocytosis these compounds also stimulated calcium-sensitive secretion of lysosomal enzymes from normal, 2–3 days starved, cells. Only uncharged 1-forms of the amino acid esters were effective. Also other lysosomotropic compounds including monodansylcadaverine, glycine-phenylalanine-2-naphthylamide, NH4Cl, and the ionophores monensin and A23187 activated starved cells. The effect of these agents (except A23187) was inhibited by the drug dantrolene suggesting that activation is a consequence of release of Ca2+ from intracellular stores. Several of the lysosomotropic agents also lost their activating effect in the presence of phospholipase A2 (PLA2) inhibitors. To investigate whether or not PLA2 activity in the cell culture could imitate the effect of the lysosomotropic agents, we incubated starved cells with snake venom PLA2s. These enzymes caused rapid, dantrolene-sensitive activation of the cells. Measurement of endogenous PLA2in “normal” cells revealed significant cellular activity but no significant secretion of the enzyme into the culture medium was observed. Together the studies with enzyme inhibitors and dantrolene suggest that the process by which lysosomotropic agents affect pinocytosis involves activation of PLA2 and release of Ca2+ from intracellular stores.
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    URL: http://dx.doi.org/10.1007/BF01273241
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    Structural basis for the red light induced repolarization of tip growth in caulonema cells ofCeratodon purpureus (1996)
    Springer
    Protoplasma 192 (1996), S. 189-198 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Microfilaments ; Microtubules ; Moss protonema ; Phototropism ; Phytochrome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two dynamic changes are associated with the phytochrome-regulated phototropic response in tip cells of the mossCeratodon purpureus: a tip-located gradient shift of chlortetracy-cline (CTC)-stained calcium and a structural reorganization of apical microfilaments (MFs). We examined the interdependence of these processes. Cells were treated with the antimicrotubule drug oryzalin, the antimicrofilament drug cytochalasin-D, and the calcium channel blocker nifedipine. respectively. The effects on phototropic growth, on the structural alignment of the cytoskeleton (microtubules, MTs; microfilaments) and on the distribution of CTC-stained calcium were studied under each of these conditions. In gravitropically growing tip cells the apical MFs form a cortical collar-like structure, consisting of actin bundles with a parallel axial alignment. These MFs point towards the presumptive growing point, a weakly stained region in the tip of the cell from which bundles are absent. MTs are present in the cortex and in the endoplasm of the tip, predominantly oriented longitudinally. The MTs converge within the central apex. The cells show a steep tip-to-base CTC-calcium gradient with its highest signal in the central apex. Destruction of MTs by 1 μM oryzalin induces several translocational effects: (i) the growing zone and phototropic outgrowth shift from the apex to subapical parts of the cell; (ii) the structural integrity of the apical MFs and the tip-to-base alignment of the CTC-calcium gradient are disturbed; and (iii) the red light induced gradient shift and the reorientation of MFs proceed in an expanded area spanning from the tip to subapical parts of the cell. Cytochalasin-D (10 μg/ml) destroys the MFs. Under these conditions tip growth stops and the phototropic outgrowth is suppressed. The apical MT-structure and the CTC-calcium gradient are not influenced by the agent. Unilateral red light still induces the light-directed translocation of the gradient. Tip cells “memorize” a unilateral irradiation applied during growth inhibition with cytochalasin-D. After recovery in darkness the cells start to grow in the former light direction. The restoration of the MFs precedes the outgrowth. The structural alignment of the rebuilt actin bundles indicates the future growth direction. The calcium channel blocker nifedipine (10 βM) also inhibits tip growth and concurrently phototropic outgrowth. Nifedipine destroys the CTC-calcium gradient and apical MFs; MTs are not influenced by the channel blocker.
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    URL: http://dx.doi.org/10.1007/BF01273891
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    In situ immunocytochemical evidence that a homolog of protein translation elongation factor EF-1α is associated with microtubules in carrot cells (1996)
    Springer
    Protoplasma 190 (1996), S. 141-150 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Calmodulin ; Carrot cells ; Elongation factor-1-alpha ; Immunofluorescence microscopy ; Microtubule-associated protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Evidence indicates that elongation factor-1α (EF-1α), a ubiquitous and abundant protein factor involved in the first step of peptide elongation, is also associated with the cytoskeleton in a variety of organisms. Although the effects of these associations on EF-1α's translational function have not been examined, the associations do appear to result in non-passive effects on the cytoskeleton. A carrot homolog of EF-1α, pp 50, has been reported to interact with microtubules in vitro, inducing the formation of microtubule bundles that can be dissociated by Ca2+/calmodulin. The characterization of anti-pp 50 antibodies is reported here. Immunocytochemistry, using anti-pp 50 and anti-tubulin antibodies, was used to investigate the co-localization of pp 50 and microtubules in situ. In carrot protoplasts fixed after detergent lysis, at least a fraction of pp 50 appears to be associated with microtubules. Treatment of such protoplasts with amiprophos-methyl (APM) reduced both the presence of microtubules and the co-localizing pp 50-associated fluorescence. In taxol-treated protoplasts, increases in both microtubules and the colocalizing pp 50-associated fluorescence were observed. When carrot protoplasts were fixed prior to detergent extraction, confocal laser scanning microscopy likewise revealed co-localization. Furthermore, what is likely to be a fluorescence resonance energy transfer (FRET) between fluorochromes associated with anti-pp 50 and anti-tubulin reporters was observed, indicating that some pp 50 is intimately associated with microtubules. The in situ cytoarchitectural evidence is consistent with a function previously proposed for pp 50 based on in vitro experiments — that pp 50 is a plant microtubuleassociated protein (MAP) whose function can be modulated by a Ca2+/calmodulin signal transduction mechanism in plant cells.
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    URL: http://dx.doi.org/10.1007/BF01281313
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    Polyanion-mediated mineralization — a kinetic analysis of the calcium-carrier hypothesis in the phytoflagellatePleurochrysis carterae (1996)
    Springer
    Protoplasma 190 (1996), S. 181-188 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Coccolithofore ; Mineralization ; Polyanion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Polyanions are postulated intermediates in biomineralization because they sequester large numbers of calcium ions and occur in high concentrations at mineralizing foci in distantly related organisms. In this study mineral ion and polyanion metabolism was examined inPleurochrysis carterae to determine whether polyanions function as intermediate calcium-carriers during coccolith (mineralized scale) formation. In this organism mineralization occurs intracellularly in coccolith-forming saccules, and mature coccoliths are extruded through the plasma membrane into the coccosphere. The polyanions (acidic polysaccharides known as PS-1 and PS-2) are synthesized in medial Golgi cisternae and transported to the coccolith-forming saccule prior to the onset of mineral deposition; they also cover the mineral surface of mature coccoliths. Pulse-chase experiments with45Ca2+ and14CO3 − show the calcium uptake into the coccolith-forming saccule is much slower than carbonate uptake. The extended intracellular half-life of calcium ions destined for the coccosphere suggests that calcium is initially sequestered in more distal Golgi elements (perhaps in association with the polyanions) and enters the coccolith-forming saccule only after passage through the endomembrane system. This is consistent with previous cytochemical studies showing that the polyanions are complexed with calcium prior to mineral deposition. It has been suggested that polyanions may be degraded at the mineralization front in order to free calcium ions for precipitation with available carbonate or phosphate ions. However, this study demonstrates that the polyanions are not degraded; essentially all PS-1 and PS-2 are eventually secreted with the mineral phase into the coccosphere. The kinetics of mineral ion and polyanion secretion are consistent with a polyanion-mediated calcium transport; however, the manner in which calcium might be sequestered by and freed from the polyanions is still obscure.
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    URL: http://dx.doi.org/10.1007/BF01281317
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    Caffeine inhibits cell plate formation by disrupting membrane reorganization just after the vesicle fusion step (1996)
    Springer
    Protoplasma 195 (1996), S. 144-155 
    Details
    ISSN: 1615-6102
    Keywords: Cytokinesis ; Tobacco ; Caffeine ; Callose ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have re-examined the effects of caffeine on cell plate formation in synchronized tobacco BY-2 cells by means of cryofixation, immunocytochemistry, and calcium staining techniques. Because cryofixation preserves structural intermediates of cell plates that are not seen in chemically fixed cells, this methodology has enabled us to define not only when caffeine acts but also which assembly steps are inhibited. Caffeine acts at an early stage of cytokinesis, just after the Golgi-derived vesicles have arrived at the cell equator and begun to fuse with each other via thin (20 nm) membrane tubules. This initial round of fusions produces a delicate membrane network which in control cells is rapidly converted in a more substantial tubulo-vesicular network covered by a thick, fuzzy coat on its cytoplasmic surface. Caffeine disrupts the conversion of the fragile, thin, fusion tube-generated membrane network into the more stable tubulo-vesicular network, the assembly of its fuzzy coat, and the budding of clathrin-coated vesicles from its surface. Normally, the tubulo-vesicular network also provides the structural framework for calcium-dependent callose synthases that deposit a callose layer over the lumenal surface of the cell plate membranes. In the presence of caffeine, no stabilizing callose layer is formed, and the thin tubule membrane network fragments into vesicles of variable sizes. Cell plates in caffeine-treated cells stained with chlortetracycline, a fluorescent stain of membrane-associated calcium, also display a significant reduction in fluorescence at the cell plate, suggesting a major decrease in cell plate membrane-associated calcium. However, this latter finding needs to be confirmed by more sophisticated calcium measuring techniques. Current theories of the mechanism of action of caffeine, including its ability to disrupt local calcium gradients, are discussed within the new ultrastructural context that this study provides. Our findings, finally, suggest a new method for isolating just fused but not further matured cell plate forming vesicles for biochemical studies.
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    URL: http://dx.doi.org/10.1007/BF01279193
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    Localized membrane-wall adhesions inPelvetia zygotes (1996)
    Springer
    Protoplasma 190 (1996), S. 39-52 
    Details
    ISSN: 1615-6102
    Keywords: F-actin ; Plasma membrane ; Cell wall ; Calcium ; Hydrogen ; Peptide RGD ; Tip growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Membrane-wall adhesions in zygotes of the brown algaPelvetia were visualized following plasmolysis. Strands of cytoplasm remained firmly attached to the cell wall at discrete adhesion sites during plasmolysis. Adhesion sites were uniformly distributed in ungerminated zygotes, but were concentrated in the apical 5 μm of the elongating rhizoid in germinated zygotes. Few adhesions were detected along the flanks of the rhizoid or in the thallus region of germinated zygotes. The structure, physiology and function of apical adhesions in the rhizoid were characterized. F-actin was found at adhesion sites in plasmolyzed zygotes labeled with rhodamine phalloidin, and disruption of cortical F-actin reduced the number of adhesions. Manipulation of cytosolic H+ and Ca2+ activities also disrupted adhesions. On the extracellular surface, the number of adhesions was reduced by inhibition of cellulose synthesis, protease cleavage of wall proteins, and changes in extracellular H+ and Ca2+ activities. Chronic treatment with the synthetic peptide RGDS, which prevents cell adhesion in fibroblasts, also reduced adhesion number. The number of adhesions per cell did not correlate with growth rate, but was inversely correlated with the ability to establish new rhizoid growth sites. The results indicate that membrane wall adhesions containing F-actin on the cytoplasmic face are localized in the growing rhizoid apex. The adhesions may be structurally related to focal adhesions in animal cells.
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    URL: http://dx.doi.org/10.1007/BF01281193
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    Localization of calcium during somatic embryogenesis of carrot (Daucus carota L.) (1996)
    Springer
    Protoplasma 190 (1996), S. 107-118 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Confocal scanning laser microscopy ; Daucus carota ; Embryogenesis ; Fluo-3 dye ; Proton microprobe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The distribution of free cytosolic Ca2+ was studied during somatic embryogenesis of carrot using confocal scanning laser microscopy with fluo-3 as a fluorescent Ca2+ indicator. Chlorotetracycline fluorescence, antimonate precipitation and proton induced X-ray emission analysis were used as additional methods to confirm the results obtained with fluo-3. The process of embryogenesis was found to coincide with a rise in the level of free cytosolic Ca2+. The level of Ca2+ was low in proembryogenic masses and relatively high in later stages of embryogenesis. The highest signal was found in the protoderm of embryos from the late globular to the torpedo-shaped stage. A gradient in fluorescence intensity was often observed along the longitudinal axis of the embryos. The most conspicuous intracellular signal was found in the nucleus. Other organelles did not take up the dye and were always without fluorescence. The changes in [Ca2+]c are discussed in relation to physiological processes which are known to be important during somatic embryogenesis.
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    URL: http://dx.doi.org/10.1007/BF01281199
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    Mineral content modifications during ripening of asparagus (Asparagus officinalis, L.) (1996)
    Springer
    Plant foods for human nutrition 49 (1996), S. 13-26 
    Details
    ISSN: 1573-9104
    Keywords: Asparagus ; Ripening ; Minerals ; Calcium ; Magnesium ; Sodium ; Potassium and phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The essential elements: calcium (Ca), magnesium (Mg), sodium (Na) potassium (K) and phosphorus (P) were analyzed in fresh asparagus to determine the effect of the ripening of the asparagus on the mineral content. Asparagus samples were classified in two groups by diameter (〈11 mm and 〉14 mm). Asparagus from a sample group with the same diameter were divided into two portions (apical and basal) according to distance from the tip. The concentrations of calcium, magnesium and phosphorus increased with the ripening process of the asparagus while the content of sodium decreased when the white asparagus turned into a green ripening state. No significant differences were established for potassium. The green ripening state was the group with the greater concentration of calcium, magnesium and phosphorus. Statistically significant differences (p〈0.001) were observed between portions of asparagus (tip and rest of stem) in the contents of the five mineral elements analyzed. The levels of mineral elements investigated increased notably in the tip of the asparagus with the exception of sodium and potassium of which the levels in the apical portion decreased or hardly modified. The variance analyses determined statistically significant differences (p〈0.001) in the concentration of magnesium, sodium and phosphorus between asparagus diameters (〈11 and 〉14 mm) and no significant differences (p〉0.05) were found for calcium and potassium. The mean element levels were (mg/kg dry weight): Ca=3240±1186; Mg=1818±490; Na=368±86; K=37297±4167 and P=6809±2491.
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    URL: http://dx.doi.org/10.1007/BF01092518
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    Characterization of the calmodulin gene family in wheat: structure, chromosomal location, and evolutionary aspects (1996)
    Springer
    Molecular genetics and genomics 252 (1996), S. 684-694 
    Details
    ISSN: 1617-4623
    Keywords: Key words Aneuploid ; Calcium ; Root ; Triticum ; Wild wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Calmodulin is a ubiquitous transducer of calcium signals in eukaryotes. In diploid plant species, several isoforms of calmodulin have been described. Here, we report on the isolation and characterization of calmodulin cDNAs corresponding to 10 genes from hexaploid (bread) wheat (Triticum aestivum). These genes encode three distinct calmodulin isoforms; one isoform is novel in that it lacks a conserved calcium binding site. Based on their nucleotide sequences, the 10 cDNAs were classified into four subfamilies. Using subfamily-specific DNA probes, calmodulin genes were identified and the chromosomal location of each subfamily was determined by Southern analysis of selected aneuploid lines. The data suggest that hexaploid wheat possesses at least 13 calmodulin-related genes. Subfamilies 1 and 2 were both localized to the short arms of homoeologous-group 3 chromosomes; subfamily 2 is located on all three homoeologous short arms (3AS, 3BS and 3DS), whereas subfamily 1 is located only on 3AS and 3BS but not on 3DS. Further analysis revealed that Aegilops tauschii, the presumed diploid donor of the D-genome of hexaploid wheat, lacks a subfamily-1 calmodulin gene homologue, whereas diploid species related to the progenitors of the A and B genomes do contain such genes. Subfamily 3 was localized to the short arm of homoeologous chromosomes 2A, 2B and 2D, and subfamily 4 was mapped to the proximal regions of 4AS, 4BL and 4DL. These findings suggest that the calmodulin genes within each subfamily in hexaploid wheat represent homoeoallelic loci. Furthermore, they also suggest that calmodulin genes diversified into subfamilies before speciation of Triticum and Aegilops diploid species.
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    Characterization of the calmodulin gene family in wheat: structure, chromosomal location, and evolutionary aspects (1996)
    Springer
    Molecular genetics and genomics 252 (1996), S. 684-694 
    Details
    ISSN: 1617-4623
    Keywords: Aneuploid ; Calcium ; Root ; Triticum ; Wild wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Calmodulin is a ubiquitous transducer of calcium signals in eukaryotes. In diploid plant species, several isoforms of calmodulin have been described. Here, we report on the isolation and characterization of calmodulin cDNAs corresponding to 10 genes from hexaploid (bread) wheat (Triticum aestivum). These genes encode three distinct calmodulin isoforms; one isoform is novel in that it lacks a conserved calcium binding site. Based on their nucleotide sequences, the 10 cDNAs were classified into four subfamilies. Using subfamily-specific DNA probes, calmodulin genes were identified and the chromosomal location of each subfamily was determined by Southern analysis of selected aneuploid lines. The data suggest that hexaploid wheat possesses at least 13 calmodulin-related genes. Subfamilies 1 and 2 were both localized to the short arms of homoeologous-group 3 chromosomes; subfamily 2 is located on all three homoeologous short arms (3AS, 3BS and 3DS), whereas subfamily 1 is located only on 3AS and 3BS but not on 3DS. Further analysis revealed thatAegilops tauschii, the presumed diploid donor of the D-genome of hexaploid wheat, lacks a subfamily-1 calmodulin gene homologue, whereas diploid species related to the progenitors of the A and B genomes do contain such genes. Subfamily 3 was localized to the short arm of homoeologous chromosomes 2A, 2B and 2D, and subfamily 4 was mapped to the proximal regions of 4AS, 4BL and 4DL. These findings suggest that the calmodulin genes within each subfamily in hexaploid wheat represent homoeoallelic loci. Furthermore, they also suggest that calmodulin genes diversified into subfamilies before speciation ofTriticum andAegilops diploid species.
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    The irreversibility of inner mitochondrial membrane permeabilization by Ca2+ plus prooxidants is determined by the extent of membrane protein thiol cross-linking (1996)
    Springer
    Journal of bioenergetics and biomembranes 28 (1996), S. 523-529 
    Details
    ISSN: 1573-6881
    Keywords: Calcium ; cyclosporin A ; mitochondria ; mitochondrial permeability transition pore ; protein oxidation ; reactive oxygen species
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract We have previously shown that mitochondrial membrane potential (δψ) drop promoted by prooxidants and Ca2+ can be reversed but not sustained by ethylene glycol-bis(β-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA) unless dithiothreitol (DTT), a disulfide reductant, is also added [Valle, V. G. R., Fagian, M. M., Parentoni, L. S., Meinicke, A. R., and Vercesi, A. E. (1993).Arch. Biochem. Biophys. 307, 1–7]. In this study we show that catalase or ADP are also able to potentiate this EGTA effect. When EGTA is added long after (12 min) the completion of swelling or δψ elimination, no membrane resealing occurs unless the EGTA addition was preceded by the inclusion of DTT, ADP, or catalase soon after δψ was collapsed. Total δψ recovery by EGTA is obtained only in the presence of ADP. The sensitivity of the ADP effect to carboxyatractyloside strongly supports the involvement of the ADP/ATP carrier in this mechanism. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of solubilized membrane proteins shows that protein aggregation due to thiol cross-linkage formed during δψ drop continues even after δψ is already eliminated. Titration with 5,5′-dithio-bis(2-nitrobenzoic acid) supports the data indicating that the formation of protein aggregates is paralleled by a decrease in the content of membrane protein thiols. Since the presence of ADP and EGTA prevents the progress of protein aggregation, we conclude that this process is responsible for both increased permeability to larger molecules and the irreversibility of δΩ drop. The protective effect of catalase suggests that the continuous production of protein thiol cross-linking is mediated by mitochondrial generated reactive oxygen species.
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    Changes in sodium, calcium and magnesium ion concentrations in sturgeon (Huso huso) urine and in kidney morphology (1996)
    Springer
    Journal of comparative physiology 165 (1996), S. 527-533 
    Details
    ISSN: 1432-136X
    Keywords: Sturgeon ; Kidney ; Urine ; Magnesium ; Calcium ; Huso huso
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract During adaptation to brackish water the young great sturgeon Huso huso is able to regulate its serum osmolarity and ion concentrations. After transfer from fresh water to brackish water the ion concentrations in the urine increase and the urine becomes isoosmotic to the blood serum after 24h. The Na+ and K+ concentrations in the urine increase during the first 12 h by 4.4 and 7.7 times, respectively, later decreasing again. The Mg2+ and Ca2+ concentrations in the urine increase by 3.4 and 14 times during the first 72h in brackish water and remain high thereafter. These results suggest that the kidneys play an important part in the regulation of serum osmolarity and in the removal of Ca2+; however, in contrast to teleosts, Mg2+ must be removed extrarenally. During adaptation to a hyperosmotic medium the diameters of the Malpighian bodies, the glomeruli and the diameter of the tubules initially all decrease, but the distal tubules become morphologically differentiated into two regions and the diameter of the distal section later increases again. It is suggested that this is the site of Ca2+ secretion into the urine.
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    Calcium signalling in isolated single chromaffin cells of the rainbow trout (Oncorhynchus mykiss) (1996)
    Springer
    Journal of comparative physiology 166 (1996), S. 396-404 
    Details
    ISSN: 1432-136X
    Keywords: Chromaffin cell ; Calcium ; Cholinergic stimulation ; Fura-2 ; Trout,Oncorhynchus mykiss
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Chromaffin cells were isolated from the posterior cardinal vein of rainbow trout (Oncorhynchus mykiss) to assess their suitability as a model system for studying mechanisms of catecholamine secretion in fish and to evaluate intracellular calcium changes associated with cholinoreceptor stimulation. Immunocytochemistry in concert with fluorescence microscopy was employed to identify characteristic chromaffin cell proteins and thus to confirm the presence of these specific cells in suspensions and cultures. Dopamine-β-hydroxylase, an enzyme of the catecholamine-synthesising Blaschko pathway, was identified in cytoplasmic vesicles of the isolated chromaffin cells. The actin filament-severing protein, scinderin, was co-localized with actin in the sub-plasmalemmal membrane of these chromaffin cells. Intracellular calcium [Ca2+]i was measured in single chromaffin cells by microspectrofluorometry using the fluorescent dye Fura-2. Significant increases in [Ca2+]i were observed in chromaffin cells in response to depolarisation of the cell membrane by high concentrations of K+ or by the stimulation of the cell by the cholinergic receptor agonists, nicotine, acetylcholine or carbachol. The response to the reversible agonist, nicotine, was attenuated following addition of the nicotinic receptor blocker hexamethonium. Such attenuation, however, did not occur when hexamethonium was added after stimulation with the non-specific irreversible cholinergic agonist, carbachol. These results demonstrate the presence of functional cholinoreceptors, linked to intracellular calcium signalling, on isolated trout chromaffin cells and reveal the potential of these cells as a model system for studying aspects of catecholamine secretion in fish.
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    Calcium signalling in isolated single chromaffin cells of the rainbow trout (Oncorhynchus mykiss) (1996)
    Springer
    Journal of comparative physiology 166 (1996), S. 396-404 
    Details
    ISSN: 1432-136X
    Keywords: Key words Chromaffin cell ; Calcium ; Cholinergic stimulation ; Fura-2 ; Trout ; Oncorhynchus mykiss
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  Chromaffin cells were isolated from the posterior cardinal vein of rainbow trout (Oncorhynchus mykiss) to assess their suitability as a model system for studying mechanisms of catecholamine secretion in fish and to evaluate intracellular calcium changes associated with cholinoreceptor stimulation. Immunocytochemistry in concert with fluorescence microscopy was employed to identify characteristic chromaffin cell proteins and thus to confirm the presence of these specific cells in suspensions and cultures. Dopamine-β-hydroxylase, an enzyme of the catecholamine-synthesising Blaschko pathway, was identified in cytoplasmic vesicles of the isolated chromaffin cells. The actin filament-severing protein, scinderin, was co-localized with actin in the sub-plasmalemmal membrane of these chromaffin cells. Intracellular calcium [Ca2+]i was measured in single chromaffin cells by microspectrofluorometry using the fluorescent dye Fura-2. Significant increases in [Ca2+]i were observed in chromaffin cells in response to depolarisation of the cell membrane by high concentrations of K+ or by the stimulation of the cell by the cholinergic receptor agonists, nicotine, acetylcholine or carbachol. The response to the reversible agonist, nicotine, was attenuated following addition of the nicotinic receptor blocker hexamethonium. Such attenuation, however, did not occur when hexamethonium was added after stimulation with the non-specific irreversible cholinergic agonist, carbachol. These results demonstrate the presence of functional cholinoreceptors, linked to intracellular calcium signalling, on isolated trout chromaffin cells and reveal the potential of these cells as a model system for studying aspects of catecholamine secretion in fish.
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    Die Bestimmung der intestinalen Strontiumabsorption — Etablierung und Validierung eines routinemäßig anwendbaren Testverfahrens (1995)
    Springer
    European journal of nutrition 34 (1995), S. 301-307 
    Details
    ISSN: 1436-6215
    Keywords: Strontium ; oraler Strontium-Test ; Calcium ; Absorption ; gesunde Probanden ; Strontium ; oral strontium test ; calcium ; absorption ; healthy volunteers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Medicine
    Description / Table of Contents: Summary Intestinal strontium absorption has been discussed recently as an indirect measure for calcium uptake. Prerequisite for the clinical use of an oral strontium test is the availability of a reliable procedure including controlled strontium supply, sample pretreatment and analysis as well as the assessment of normal values. In the present study, a group of young females (n=33; 24.0 ± 2.7 y; BMI 21.5 ± 1.9) received an oral dose of 2.27 mmol strontium in a standardized breakfast that contained 0.625 mmol calcium. Before and 220 min after the bolus serum strontium concentrations were determined by means of atomic absorption spectrophotometry (coefficient of variation: within day 4.8 %, n=10; day-to-day 9.5 %, n=8). The error of the method was 2.7 %. Calculation of the fractional strontium absorption rate considered the respective distribution volume (extracellular fluid; either estimated using body weight or determined by means of bioimpedance analysis [BIA]). Average absorption rates were 13.3 ± 3.1 % and, considering BIA measurement 13.6 ± 2.6 %, respectively. Smoking, exercise and, use of oral contraceptives showed no effects. Our oral strontium test is characterized by excellent reliability, easy handling and low costs and, thus, is suitable for routine use.
    Notes: Zusammenfassung Die Erfassung der Strontiumabsorption wird heute als indirektes Verfahren zur Beurteilung der intestinalen Calciumabsorption diskutiert. Voraussetzung für die klinische Anwendung ist ein vertrauenswürdiges Testverfahren inclusive kontrollierter Strontiumgabe, Probenaufarbeitung und -analyse sowie die Erfassung von Normalwerten. Für unsere Studien wurde ein Kollektiv junger Frauen (n=33, 24,0 ± 2,7 Jahre; BMI 21,5 ± 1,9) herangezogen. Die Probandinnen erhielten eine Bolusgabe von 2,27 mmol Strontium zusammen mit einem Standardfrühstück (ca. 0,625 mmol Calcium). Vor und 220 min nach der Bolusgabe erfolgte die Bestimmung des Serum-Strontiumgehaltes mittels Atomabsorptionsspektrometrie. Der Variationskoeffizient der Methode lag innerhalb eines Tages bei 4,8 % (n=10) und von Tag zu Tag 9,5 % (n=8). Der Fehler der Methode betrug 2,7 %. Die Berechnung der fraktionellen Strontiumabsorptionsrate erfolgte unter Berücksichtigung des entsprechenden Verteilungsraumes (Extrazellulärflüssigkeit; Schätzverfahren über Körpergewicht bzw. Bioimpedanz-Analyse [BIA]). Die Strontiumabsorptionsrate lag im Mittel bei 13,3 ± 3,1 %, unter Berücksichtigung der BIA-Werte bei 13,6 ± 2,6 %. Rauchen, sportliche Aktivität bzw. Einnahme oraler Kontrazeptiva zeigten keinen Einfluß. Das hier vorgestellte Testverfahren ist aufgrund seiner hohen Vertrauenswürdigkeit und relativ einfacher Handhabung für Routine-untersuchungen geeignet.
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    Chronic overcrowding decreases cytoplasmic free calcium levels in T lymphocytes of aged CBA/CA mice (1995)
    Springer
    Cellular and molecular life sciences 51 (1995), S. 976-979 
    Details
    ISSN: 1420-9071
    Keywords: Calcium ; T lymphocytes ; aging ; psychosocial stress ; overcrowding ; animal housing ; lymphocyte activation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Intracellular calcium concentration is a sensitive marker of the homeostasis of living cells, and its increase is an essential step of T lymphocyte activation. Changes in the environment provoke an adaptive stress-response of the organism. In our present work we have investigated the effect of chronic overcrowding on resting and lectin-stimulated cytoplasmic free calcium concentration of splenic T lymphocytes from young and aged CBA/CA mice (50 animals total). The animals were kept under ‘normal’ (68 cm2/animal) or ‘overcrowded’ (22 cm2/animal) conditions for 3 months. Young animals showed no change in resting and stimulated calcium after overcrowding. T cells from aged mice, however, displayed significantly smaller levels of both resting and lectin-stimulated intracellular calcium concentration (p〈0.01 each), as compared to those of the non-stressed, aged animals. This inadequate adaptation in the calcium metabolism of T lymphocytes may significantly contribute to the diminished immune response of the aged in stress.
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    Mycorrhizal infection and ageing affect element localization in short roots of Norway spruce [Picea abies (L) Karst.] (1995)
    Springer
    Mycorrhiza 5 (1995), S. 417-422 
    Details
    ISSN: 1432-1890
    Keywords: Calcium ; Iron ; Lead ; Phosphorus ; Short roots ; X-ray microanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Norway spruce [Picea abies (L.) Karst.] seedlings, nonmycorrhizal of mycorrhizal with Laccaria laccata or Paxillus involutus were grown in a quartz sand-nutrient solution system for 6 months and then treated with 5 μM Pb for 4 days. Element contents of cortex cell wall of young, medium and old short roots were determined by X-ray microanalysis of longitudinal thin sections. The Pb content was influenced neither by age nor by the distance from the root tip (up to 1.7 mm) but was significantly lower in the P. involutus mycorrhizae than in the L. laccata mycorrhizae or in nonmycorrhizal short roots. In the P. involutus mycorrhizae, the P content of the cortex cell walls was twice as high in young mycorrhizae than in old mycorrhizae. In the nonmycorrhizal short roots and the L. laccata mycorrhizae, P content was influenced neither by age nor by distance from the root tip. The Ca and Fe contents of the cortex cell walls increased with age in the nonmycorrhizal short roots and the mycorrhizae. It is concluded that the element content of the cortex cell walls of short roots is strongly influenced by age, while the distance from the root tip seems to be of minor importance.
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    The concentration of Ca, Sr, Ba and Mn in successive needle age classes of Norway spruce [Picea abies (L.) Karst.] (1995)
    Springer
    Trees 10 (1995), S. 31-39 
    Details
    ISSN: 1432-2285
    Keywords: Calcium ; Barium ; Manganese ; Strontium ; Picea abies needles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The concentrations of Ca, Sr, Ba and Mn were determined in up to five successive needle age classes from 54 individual Norway spruce trees [Picea abies (L.) Karst] from nine different sites. The accumulation behaviour was found to be very nonuniform, going from an increase with needle age to a decrease; irregular patterns were also found. The type of accumulation is largely site specific. The increasing behaviour can in most cases be approximated by a simple arithmetic function. All four elements usually show the same accumulation pattern, the similarities being closest between Ca and Mn and least between Ca and Ba. It is postulated that the similarity between the four elements is due to their precipitation and storage as oxalates. The similarity between Ca, Sr and Ba is observed at all concentrations, that with Mn only at concentrations larger than 300 μg/g. Mn at small concentrations (〈 50 μg/g) shows a decreasing pattern and no similarity at all with Ca, Sr and Ba, but behaves similar to mobile elements.
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    Continuous measurement of changes in intracellular calcium concentration in mouse splenic T cells attached to a glass substrate (1995)
    Springer
    Journal of biomedical science 2 (1995), S. 379-383 
    Details
    ISSN: 1423-0127
    Keywords: T cell ; Cell Tak® ; Calcium ; Superfusion ; Spectrofluorometer ; Confocal microscopy ; Concanavalin A ; Isoproterenol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Mitogen- and isoproterenol-induced changes of [Ca2+]i in T cells attached to a glass substrate were examined. Murine (C57BL/6) splenic T cells were attached to coverslips or 35-mm dishes (MatTek) precoated with Cell Tak® (3.5 µg/cm2). The cells were then loaded with fluorescent dye (2 µg/ml of fura2-AM or fluo3-AM) and changes in [Ca2+]i in a population of cells (using a spectrofluorometer) or in single cells (using a confocal microscope) were measured during continuous superfusion. Population measurements of [Ca2+]i demonstrated that concanavalin A (Con A, 2 or 5 µg/ml) caused an increase in [Ca2+]i that rose to a peak and then declined to a steady state. The concentration-response relationship (0.05–5 µg/ml) had an EC50 of ∼0.3 µg/ml. Isoproterenol decreased the Con A-induced elevation of steady state [Ca2+]i. In single cell studies, the increase in [Ca2+]i in response to Con A typically occurred in about 50% of the cells in a microscope field, and the delay before activation varied among cells. Taken together, these data demonstrate that Cell Tak® can be used to attach T cells to glass coverslips and will be useful for the study of signaling mechanisms in T cells.
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    Regulation of renal calbindin-D28K: The role of calcitonin (1995)
    Springer
    Calcified tissue international 56 (1995), S. 372-375 
    Details
    ISSN: 1432-0827
    Keywords: Calcitonin ; Calcium ; Renal calbindin-D28k ; Intestinal calbindin-D9k ; 1,25(OH)2D3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Infusion of calcitonin lowers circulating calcium, but in the distal tubule of the kidney, pharmacological doses of calcitonin increase the active calcium reabsorption. Calbindin-D28k plays a significant role in the calcium reabsorption in the distal convoluted tubule of the kidney. The effect of calcitonin on renal calbindin-D28k in relation to calcium metabolic changes was therefore examined. In study 1, thyroparathyroidectomy followed by autotransplantation of the parathyroid glands (TX) was compared with a sham operation in rats. TX reduced plasma calcitonin from 54±2 to 9±1 pg/ml (P〈0.001), whereas ionized calcium and parathyroid hormone were returned to the control value after an initial decrease, indicating a successful implantation of the parathyroid glands. No changes were seen in calbindin-D or plasma 1,25(OH)2D. In study 2, subcutaneous infusion of salmon calcitonin 2.5 U/kg/hour via osmotic pumps was compared with infusion of vehicle in rats. Ionized calcium was reduced from 1.37±0.01 to 1.33±0.02 mmol/liter (P〈0.05), whereas no changes were seen in renal or intestinal calbindin-D or in plasma 1,25(OH)2D. After TX, only calcitonin decreased whereas the other calcium metabolic parameters showed no change. This indicates that in rats, selective elimination of calcitonin does not influence other parameters of the calcium metabolism and that the effect of calcitonin on calcium transport in the distal tubule is not mediated via an increase in renal calbindin-D28k.
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    Calcium tracer kinetics show decreased irreversible flow to bone in glucocorticoid treated patients (1995)
    Springer
    Calcified tissue international 56 (1995), S. 533-535 
    Details
    ISSN: 1432-0827
    Keywords: Calcium ; Kinetics ; Stable isotope ; Glucocorticoids ; Osteopenia ; Mathematical modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Osteopenia resulting from pharmacologic doses of glucocorticoids is well known. Previously, there has been no satisfactory quantitative model describing the kinetics of calcium flow in subjects on chronic steroid use. A mathematical model of calcium isotope interaction with bone is described and applied to determine an estimate of kinetic parameters characterizing these changes. Calcium tracer dilution kinetics after a bolus injection of 42Ca were measured in 14 subjects with juvenile dermatomyositis, 6 on predinisone regimens and 8 on treatment regimens without prednisone. Irreversible tracer loss from plasma bone is found to be significantly reduced (P=0.043) in the glucocorticoidtreated patients compared with patients on nonsteroid regimens. Reversible flow to bone is noted to be similar in the two groups. These results suggest a direct effect of glucocorticoids on osteoblast function.
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    Parathyroid hormone decreases in vivo insulin effect on glucose utilization (1995)
    Springer
    Calcified tissue international 57 (1995), S. 127-132 
    Details
    ISSN: 1432-0827
    Keywords: Parathyroid hormone ; Insulin ; Glucose metabolism ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Hyperparathyroidism is associated with impaired glucose tolerance, and parathyroidectomy may improve carbohydrate homeostasis. It has been suggested that parathyroid hormone (PTH) suppresses insulin secretion but it is unclear whether it also interferes with the peripheral action of insulin. To evaluate in vivo effects of PTH on insulinmediated glucose utilization, 15 male Sprague Dawley rats were continuously infused with rat PTH (1–34) using an Alzet miniosmotic pump at a rate of 0.03 nm/hour. Controls were infused with the vehicle alone. Following 5 days of PTH infusion, plasma calcium (Ca) levels were higher in the PTH-infused rats (12.3±0.2 versus 9.9±0.1 mg/dl, P〈0.01). On the 5th day, glucose (700 mg/kg) and insulin (0.175 U/kg) were given as a bolus infusion through the left femoral vein, blood samples were obtained from the right femoral vein, and plasma glucose and insulin were measured at basal (0 minutes) and at 2, 5, 10, and 20 minutes postinfusion. Basal, nonfasting glucose levels were higher (166±4 versus 155±4 mg/dL, P〈0.04) in the PTH-infused rats but their insulin levels were similar to those of controls (6.5±0.6 versus 5.6 ±0.5 ng/ml). Postinfusions and maximal (2 minutes) glucose and insulin levels were similar in both groups. However, although insulin levels were similar in both groups at all measured time points, glucose levels at 20 minutes were higher in the PTH-treated rats (205±13 versus 173±9; P〈0.03). Also, calculated glucose disappearance rates (Kg) were decreased in the PTH-infused rats (4.05±0.3 versus 4.63±0.8; P=0.054), suggesting an impaired peripheral effect of insulin on glucose utilization. To gain insight into the potential contribution of the hypercalcemia or the PTH to these abnormalities, correlation evaluations were performed. Only in PTH-infused rats did plasma Ca correlate with plasma glucose at 0 and 20 minutes (r=0.6, P=0.02; r=0.7, P=0.01) and with the area under the glucose curve (r=0.6, P=0.03) during the glucose-insulin infusion. Also only in PTH-infused rats did PTH correlate with 0 (P=0.07) and 20-minute (P=0.02) plasma glucose levels. There was no correlation between either Ca or PTH and basal insulin levels or the area under the insulin curve in either group. Consequently, we suggest that in the rat, PTH infusion associated with hypercalcemia impairs insulin effect on glucose utilization in vivo and this defect may be induced by the Ca, PTH, or both.
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    The influence of fluoride on the adsorption of proteoglycans and glycosaminoglycans to hydroxyapatite (1995)
    Springer
    Calcified tissue international 56 (1995), S. 236-239 
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    ISSN: 1432-0827
    Keywords: Proteoglycan ; Glycosaminoglycans ; Dentine ; Fluoride ; Biomineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Proteoglycans and their spatial arms, the glycosaminoglycans, are known to interact with hydroxyapatite, and are considered to have a role in the regulation of mineralization. This study investigates the interactive mechanisms, with particular attention directed at the influence of fluoride on the adsorption process. Proteoglycans and glycosaminoglycans were adsorbed to hydroxyapatite in the presence of fluoride (1–20 ppm range). The adsorbates included a chondroitin 4-sulfate-rich proteoglycan extracted from rat incisor dentine, hyaluronan, chondroitin 4-sulfate, and dermatan sulfate. The order of glycosaminoglycan in decreasing affinity for hydroxyapatite was chondroitin 4-sulfate, dermatan sulfate, and hyaluronan, and the individual glycosaminoglycans showed different responses to the presence of fluoride. Graded increases in fluoride (1–4 ppm) led to 5–40% reduction of glycosaminoglycan adsorption to hydroxyapatite. The proteoglycan showed less affinity for hydroxyapatite, and demonstrated a reduction in adsorption of up to 22% with 20 ppm fluoride. The inhibitory effect of fluoride indicated an electrostatic mechanism, presumably via the calcium sites in the hydroxyapatite lattice.
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    Effect of stopping fluoride administration on the distribution profiles of fluoride in three different kinds of rat bones (1995)
    Springer
    Calcified tissue international 56 (1995), S. 292-296 
    Details
    ISSN: 1432-0827
    Keywords: Fluoride ; Bone ; Defluoridation ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract The aim of this work was to explore the reduction of fluoride concentrations in the skeleton after stopping experimental fluoride administration. Fluoride was administered to the rats at varying doses (0, 50, 100 ppm in drinking water) and for different lengths of time (4, 13, 25 weeks). A series of fluoride concentrations across the full thickness of humerus, parietal bone, and vertebra arch in rats were measured by means of an abrasive micro-sampling technique. The distribution profiles of fluoride from periosteal to endosteal surfaces, which were apparently related to the histological structure of these bones, were U shaped in the humerus, V shaped in the parietal bone, and W shaped in the vertebra arch. The average fluoride concentrations in the bones increased significantly with each increasing dose and length of fluoride administration. The relative increments were similar between the different regions or the different bones. After stopping fluoride administration, on the other hand, the relative reduction of the average fluoride concentrations in the bones were 30–100%. They were greatly related to the length after stopping fluoride administration and the dose and length of fluoride administration, but also dependent upon the type of bone and the region examined.
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    Prevention of postmenopausal bone loss by rectal calcitonin (1995)
    Springer
    Calcified tissue international 56 (1995), S. 539-542 
    Details
    ISSN: 1432-0827
    Keywords: Calcium ; Calcitonin ; Densitometry ; Menopause ; Osteoporosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract A group (150) of healthy women, who had been menopausal for less than 5 years and who had never received any form of treatment to prevent bone loss were entered into a randomized, controlled study comprising three arms. They were randomly allocated to the double-blind administration of five suppositories per week containing either 100 IU of salmon calcitonin or a placebo, or to a group receiving a suppository containing 200 IU of salmon calcitonin three times per week. All women received 500 mg/day of calcium supplementation. After 12 months, bone mineral density (BMD) of the spine, measured by dual energy X-ray absorptiometry, decreased significantly (P〈0.01) in the placebo group by 3.1% (SD: 3.6%) but did not change in the two calcitonin groups [+1.3% (3.5%) with 100 IU/day and +2.3% (4.0%) with 200 IU 3/week]. The differences in response between the placebo group and the two calcitonin groups were significant (P〈0.05), but the difference between the two regimens of calcitonin administration was not. No differences appeared among the three groups for the response at the level of the hip. Evolution of biochemical markers reflecting bone turnover did not differ significantly among groups. Nearly 40% of the women withdrew prematurely because of local (rectal or intestinal) intolerance to repetitive suppositories, with a nonsignificantly different frequency in the placebo or calcitonin groups. We conclude that rectal calcitonin might be an interesting preventive approach against trabecular postmenopausal bone loss but that long-term acceptability of suppositories should be evaluated in view of each patient's sensibility or cultural background.
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    Diet, bone mass, and osteocalcin: A cross-sectional study (1995)
    Springer
    Calcified tissue international 57 (1995), S. 86-93 
    Details
    ISSN: 1432-0827
    Keywords: Bone density ; Calcium ; Diet ; Osteocalcin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract To determine the relationships among nutrient intake, bone mass, and bone turnover in women we have investigated these issues in a population-based, crosssectional, observational study in one county in central Sweden. A total of 175 women aged 28–74 at entry to the study were included. Dietary assessment was made by both a semiquantitative food frequency questionnaire and by four 1-week dietary records. Dual energy X-ray absorptiometry was performed at five sites: total body, L2–L4 region of the lumbar spine, and three regions of the proximal femur. Serum concentrations of osteocalcin (an osteoblast-specific protein reflecting bone turnover) were measured by a radioimmunoassay. Linear regression models, with adjustment for possible confounding factors, were used for statistical analyses. A weak positive association was found between dietary calcium intake as calculated from the semiquantitative food frequency questionnaire and total body bone mineral density (BMD) among premenopausal women. No association emerged between dietary calcium intake and sitespecific bone mass, i.e., lumbar spine and femoral neck, nor was an association found between dietary calcium intake and serum osteocalcin. BMD at some of the measured sites was positively associated with protein and carbohydrates and negatively associated with dietary fat. In no previous studies of diet and bone mass have dietary habits been ascertained so carefully and the results adjusted for possible confounding factors. Neither of the two methods of dietary assessment used in this study revealed any effect of calcium intake on BMD at fracture-relevant sites among these healthy, mostly middle-aged women. A weak positive association was found between calcium intake estimates based on the food frequency questionnaire and total body BMD. In this study population the preventive effect of high dietary calcium on osteoporosis is probably very weak. The independent significance of protein, carbohydrates, and fat is uncertain.
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    Egg shell quality, clutch size and hatching success of the great tit (Parus major) and the pied flycatcher (Ficedula hypoleuca) in an air pollution gradient (1995)
    Springer
    Oecologia 102 (1995), S. 312-323 
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    ISSN: 1432-1939
    Keywords: Pollution ; Acidification ; Breeding success ; Heavy metal ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Egg shell thickness, egg volume, clutch size and hatching success of Parus major and Ficedula hypoleuca were studied at 14 study sites around a copper smelter complex in Harjavalta, south-west Finland, in 1991–1993. In 1991–1992 unhatched eggs were collected to measure shell quality. F. hypoleuca was more susceptible to pollutants than P. major, the response of which was weaker in all aspects studied. Egg shells of F. hypoleuca were about 17% thinner and eggs were about 8% smaller in volume near the factory than at a distance of 10 km. The clutch size of F. hypoleuca was significantly smaller and hatching success markedly lower at a study site next to the factory complex than at all other sites. In P. major, variation in shell thickness and egg volume was not significantly related to the distance from the pollution source. Clutch size and hatching success of P. major did not significantly differ among study sites, although the trend in hatching success was in the same direction as in F. hypoleuca. Clutches of both species contained less shell material and both species had more nests without eggs near the factory than further away. The surface structure of the eggshells was studied by scanning electron microscope. Especially in F. hypoleuca, the egg shell surface was more rough and porous near the factory. The roles of Ca and heavy metals in shell thinning are discussed.
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    Diversity of calcium-efflux transporters in wheat aleurone cells (1995)
    Springer
    Planta 197 (1995), S. 19-30 
    Details
    ISSN: 1432-2048
    Keywords: Aleurone ; ATPase ; Calcium ; Calmodulin ; Membrane Transport ; Triticum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The ability of plant cells to regulate cellular calcium is dependent upon the action of calcium-transport proteins. Although significant progress has been made in identifying calcium-transporter activities (CaTs) in a number of plant tissues, very little is known about the diversity of CaTs in any single differentiated cell type. We have used isolated membrane vesicles from wheat (Triticum aestivum L.) aleurone cells to identify and characterize the principal CaTs that are responsible for efflux of Ca2+ from the cytosol of this highly differentiated cell. Based on the sensitivity of transport to protonophores and on their buoyant density in isopycnic sucrose density gradients, our data show that at least three prominent CaTs can be distinguished in membrane vesicles from aleurone cells. Two of these CaTs, which we have named Type I and Type III, were insensitive to protonophores and were inhibited by vanadate or erythrosin B (EB). Type I was associated with a membrane fraction enriched in endoplasmic reticulum whereas Type III was associated with the plasma membrane. The third prominent CaT, Type II, was inhibited by protonophores and by nitrate and was associated with a membrane fraction enriched in tonoplast. The three CaTs differed significantly in their intrinsic properties. Type I had the highest affinity for Ca2+ (K m, 0.15 μM), was stimulated by oxalate, inhibited by vanadate and erythrosin B, and was unaffected by exogenous calmodulin. Type II exhibited complex kinetics with regard to Ca2+ and was best described as a combination of a low-affinity (K m, 21 μM) and a high-affinity component (K m, 0.2 μM). Type II CaT was stimulated by calmodulin (1 μM) and oxalate, and was inhibited by dicyclohexylcarbodiimide (500 μM). Finally, Type III had an intermediate affinity for Ca2+ (K m, 2.0 μM), was not stimulated by calmodulin or by oxalate, and was inhibited by low concentrations of erythrosin B (0.1 μM). These data provide one of the first comparative investigations of the Ca2+-transport activities in a single highly differentiated cell type. They indicate that at least three CaTs function to regulate cellular Ca2+ and we speculate that cytosolic Ca2+ may be buffered primarily by Type II and Type III CaTs which are associated with an acidic intracellular compartment, probably the vacuole, and with the plasma membrane.
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    Effects of calcium, magnesium, potassium and boron on sperm cells isolated from pollen of Zea mays L. (1995)
    Springer
    Sexual plant reproduction 8 (1995), S. 113-122 
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    ISSN: 1432-2145
    Keywords: Zea mays ; Calcium ; Cell integrity ; Cell viability ; Sperm cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Our previous studies showed that Brewbaker and Kwack salts, which have been widely used in pollen germination and sperm isolation, are not appropriate for the maintenance of isolated maize (Zea mays L.) sperm cells. In the present study, we have characterized the effects of each BKS component salt on the integrity of isolated sperm cells using hemacytometry. At 0.01 and 0.1 mM, there were no differences in cell number between control and any salt-treated cells except a 22% decrease with 0.1 mM MgSO4 at 48 h. At the 1 mM level, cell number decreased with time in the presence of Ca(NO3)2 and MgSO4, with loss of integrity of most cells at 48 h, while KNO3 and H3BO3 had little or no effect. Further characterization of calcium-induced reduction in cell integrity using flow cytometry showed that depletion of possible residual free calcium by addition of EGTA to the suspension medium improved cell longevity and viability. Exposure of isolated sperm cells to 1 mM calcium had no effect on cell integrity and viability in 5 h; however, only 12% of cells remained intact at 24 h. The reduction in cell integrity was hastened when cells were pretreated with the calcium ionophore A23187 prior to exposure to 1 mM calcium, with a 54% reduction in cell number at 1 h and complete cell lysis at 24 h. However, depletion of cytosolic free calcium by pretreatment of cells with the calcium ionophore followed by resuspension in the presence of EGTA resulted in rapid reduction of cell integrity as well. These results collectively suggest that maize sperm cells are sensitive to exogenous free calcium; however, a certain level of cytosolic free calcium is necessary for maintenance of integrity. Mechanisms of calcium-induced reduction in cell integrity are discussed along with possible roles of the sensitivity of sperm cells to calcium in fertilization.
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    Calcium restriction induces cardenolide accumulation in cell suspension cultures of Digitalis thapsi L. (1995)
    Springer
    Plant cell reports 14 (1995), S. 786-789 
    Details
    ISSN: 1432-203X
    Keywords: Digitalis thapsi ; Calcium ; Digitoxin ; Digoxin ; Suspension cultures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The removal of calcium ions from Murashige and Skoog culture medium induced a marked increase in the accumulation of cardenolides in cell suspension cultures of Digitalis thapsi. Cell viability was not affected although growth was slightly reduced. Strontium ions could substitute for calcium in inhibiting cardenolide production, this effect of calcium being reversed by the addition of LaCl3 or ethyleneglycol-bis-(β-aminoethyl ether)-N,N′-tetraacetic acid. The results suggest that calcium, apart from its general effects on growth, may play a role in the regulation of cardenolide metabolism in a concentration dependent manner.
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    URL: http://dx.doi.org/10.1007/BF00232923
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    Hydrogen fluoride effects on plasma membrane composition, ATPase activity and cell structure in needles of eastern white pine (Pinus strobus) seedlings (1995)
    Springer
    Trees 9 (1995), S. 190-194 
    Details
    ISSN: 1432-2285
    Keywords: Plasma membrane ; Fluoride ; ATPase ; Sterols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Eastern white pine (Pinus strobus L.) seedlings were grown in controlled environment growth cabinets and fumigated with 0.4 and 1.6 μg m−3 hydrogen fluoride for 2–28 days. Plasma membranes were isolated from needles of treated and control seedlings and their chemical composition and ATPase activity examined to determine early effects of hydrogen fluoride action. In plants treated for 2 days with both fluoride levels, ratios of plasma membrane free sterols:phospholipids and sterols:proteins were drastically higher than ratios in control plants. Seedlings treated with hydrogen fluoride for 8 days contained plasma membranes with elevated phospholipid:protein and sterol:protein ratios and their plasma membrane ATPase activity was higher than that of control plants. Prolonged, 28-day hydrogen fluoride treatment with 1.6 μg m−3 level was the only treatment which produced a drastic inhibition of plasma membrane ATPase activity. During the initial stages of hydrogen fluoride treatment, treated cells did not show alterations of ultrastructure which were previously shown in cells of plants treated with soil applied sodium fluoride. The results of the present study indicate that the plasma membranes may be among the initial sites of hydrogen fluoride injury to plants as well as initial sites of defense reaction.
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    Combined effects of nitrogen and elevated CO2 on soils from controlled environment studies (1995)
    Springer
    Water, air & soil pollution 85 (1995), S. 1551-1556 
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    ISSN: 1573-2932
    Keywords: Nitrogen ; Carbon dioxide ; Phosphorus ; Calcium ; Potassium ; Magnesium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This paper describes the effects of elevated CO2 and N fertilization on soils planted with ponderosa pine (Pinus ponderosa) seedlings in short-term greenhouse studies. The high degree of homogeneity in the soils used allowed sensitive evaluation of soil changes in response to treatments. Elevated CO2 had no detectable effect upon soil N availability, but both CO2 and N fertilization caused significant changes in soil available (NH4F/HCl-extractable) P. Some of these changes could be accounted for by plant uptake, some were apparently due to differences in P immobilization (biotic or abiotic). N fertilization caused reductions in exchangeable K, Ca and Mg which could not be accounted for by plant uptake and were probably due to increased leaching. None of the reductions in soil available nutrients observed were of sufficient magnitude to cause nutrient deficiencies over the approximate 1-year duration of these studies.
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    URL: http://dx.doi.org/10.1007/BF00477201
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    Lipid structure and Ca2+-ATPase function (1995)
    Springer
    Bioscience reports 15 (1995), S. 289-298 
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    ISSN: 1573-4935
    Keywords: ATPase ; Calcium ; phospholipid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Effects of lipid structure on the function of the Ca2+-ATPase of skeletal muscle of sarcoplasmic reticulum are reviewed. Binding of phospholipids to the ATPase shows little specificity. Phosphatidylcholines with short (C14) or long (C24) fatty acyl chains have marked effects on the activity of the ATPase, including a change in the stoichiometry of Ca binding. Low ATPase activity in gel phase lipid follows from low rate of phosphorylation. Phosphatidylinositol 4-phosphate increases ATPase activity by increasing the rate of dephosphorylation of the phosphorylated ATPase. Stimulation is not seen with other anionic phospholipids; phosphatidic acid decreases ATPase activity in a Mg2+-dependent manner.
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    Luminal calcium regulation of calcium release from sarcoplasmic reticulum (1995)
    Springer
    Bioscience reports 15 (1995), S. 387-397 
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    ISSN: 1573-4935
    Keywords: Calcium ; Ca2+-channel ; inosital phosphate ; ryanodine ; sarcoplasmic reticulum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract This article discusses how changes in luminal calcium concentration affect calcium release rates from triad-enriched sarcoplasmic reticulum vesicles, as well as single channel opening probability of the ryanodine receptor/calcium release channels incorporated in bilayers. The possible participation of calsequestrin, or of other luminal proteins of sarcoplasmic reticulum in this regulation is addressed. A comparison with the regulation by luminal calcium of calcium release mediated by the inositol 1,4,5-trisphosphate receptor/calcium channel is presented as well.
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    Calcium modulates rapid protein phosphorylation/dephosphorylation in isolated eyespot apparatuses of the green alga Spermatozopsis similis (1995)
    Springer
    Planta 197 (1995), S. 343-351 
    Details
    ISSN: 1432-2048
    Keywords: Calcium ; dependent protein phosphorylation ; Eyespot apparatus ; Phototaxis ; Protein kinase ; Protein phosphatase ; Spermatozopsis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We present an initial characterization of protein kinase and phosphatase activities associated with isolated eyespot apparatuses, the organelle involved in blue/ green-light-mediated behavioural responses of flagellate green algae. In the presence of the phosphatase inhibitors okadaic acid and vanadate, rapid overall protein phosphorylation (t0.5 ≈ 10 s) was observed. The majority of protein kinase activities and their substrates were identified as integral or tightly-bound peripheral membrane proteins. While vanadate generally increased the phosphate incorporation into all phosphoproteins, okadaic acid specifically enhanced phosphorylation of proteins in the range of 39–43 kDa. In contrast to all other phosphoproteins in this subcellular fraction, two proteins with apparent molecular masses of 83 and 16 kDa shared remarkable similarities: (i) They exhibited a fast turnover of the 32P-label, even in the presence of phosphatase inhibitors, and (ii) their dephosphorylation was delayed at 10−8 M free Ca2+. In addition, the 16-kDa protein underwent thiophosphorylation. The general in-vitro phosphorylation pattern was strongly influenced by alterations of free Ca2+ in a concentration range known to affect responses related to phototactic and photophobic behaviour of this alga (10−8 M to 10−7 M). However, characteristics of Ca2+-calmodulin-dependent protein kinases were not observed, i.e. exogenous calmodulin and trifluoperazine had no significant effect on protein phosphorylation. Also exogenous lipids (phosphatidylserine, diacylglycerol), inhibitors of cGMP and cAMPdependent protein kinases and protein kinase C (H-7 and HA1004) as well as exogenously added cGMP and cAMP did not potentiate or inhibit protein phosphorylation. These characteristics of the kinase activity in our fraction most closely resemble those of the plant- and protist-specific group of Ca2+-dependent, calmodulin-independent protein kinases. In-situ phosphorylation experiments following electrophoretic separation revealed the presence of three putative Ca2+-dependent kinases or their catalytic subunits (77,48 and 47 kDa) in the eyespot preparation. In addition, a Ca2+-independent activity at 28 kDa was detected. Possible roles of reversible protein phosphorylation in eyespot apparatuses are discussed.
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    Protons and calcium modulate SV-type channels in the vacuolar-lysosomal compartment — channel interaction with calmodulin inhibitors (1995)
    Springer
    Planta 197 (1995), S. 655-671 
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    ISSN: 1432-2048
    Keywords: Calcium ; Calmodulin antagonists ; pH ; SV-type channels (vacuole) ; Taproot, guard cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Slowly activating vacuolar (SV-type; Hedrich and Neher 1987, Nature 329: 833–835) ion channels provide the predominant membrane conductance of the vacuolar-lysosomal compartment of Vicia faba L. guard cells and sugar beet (Beta vulgaris L.) taproots. Applying the patch-clamp technique to isolated vacuoles of both tissues, the electrical and pharmacological properties of guard-cell SV-type currents were studied and compared to the sugar beet channel with regard to its modulation by cytoplasmic Ca2+ and pH. This outward rectifier of V. faba guard cells showed a half-maximum activation at 55–60 mV with an apparent gating charge equivalent of z ≈ 4. Studies on the single-channel and whole-vacuole level revealed an extremely high conductance of 280 pS for the guard-cell channels at a mean density of 0.37 μm-2 compared to taproots (120–140 pS at about 0.16 channels per μm2). Guard-cell SV-type channels are weakly selective for cations over anions and lack saturation at KC1 concentrations of up to 1 M. Since in the absence of physiological K+ concentrations, Ca2+ is the major permeable ion, relative changes in the amounts of the two ions might control the permeation process. In spite of their different origins and physiological functions, in guard cells and beet taproot cells, cytoplasmic Ca2+ and protons, both considered as candidates for intracellular signalling in plants, modulate the voltage dependence of SV-type channels. While the two effectors do not alter the single-channel conductance, they strongly interact with the voltage sensor. The calmodulin (CaM) antagonists N-(6-aminohexyl)-5-chloro-l-naphthalenesulfonamide hydrochloride (W-7), trifluoperazine (TFP) and calmidazolium hydrochloride (R 24571) effectively blocked the channel in an antagonist-specific manner. In agreement with the properties of a Ca2+-permeable channel, CaM could be involved in the modulation of the activation threshold of the SV-type channel. We therefore conclude that guard-cell SV-type channels, which might be responsible for the release of K+, Cl- and to a smaller extent Ca2+ during stomatal closure, could serve as an intracellular sensor for changes in cytosolic calcium (calcium-CaM) and pH.
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    Transduction of chemostimuli by the type I carotid body cell (1995)
    Springer
    The journal of membrane biology 144 (1995), S. 1-9 
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    ISSN: 1432-1424
    Keywords: Carotid body ; Hypoxia ; Acidosis ; Ion channels ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The postulated mechanisms for hypoxic and acidic chemotransduction by type I cells that we have described here are summarized in the diagrams of Fig. 4. Most if not all of these require more complete evaluation and, as we have described, there are obvious points of contention that need to be resolved. Nevertheless, it is apparent that studies of isolated type I cell preparations carried out over the last six years have provided significant advancements in our understanding of chemotransduction in the type I cell. Only when the functioning of these cells has been fully described can we hope to understand the mechanisms underlying the responses of the intact organ to chemostimuli.
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    Magnitude and modulation of pancreatic β-cell gap junction electrical conductance in situ (1995)
    Springer
    The journal of membrane biology 146 (1995), S. 163-176 
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    ISSN: 1432-1424
    Keywords: Pancreatic islet ; Cell-to-cell coupling ; Calcium ; Burst ; Synchrony ; Insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The parallel gap junction electrical conductance between a β-cell and its nearest neighbors was measured by using an intracellular microelectrode to clamp the voltage of a β-cell within a bursting islet of Langerhans. The holding current records consisted of bursts of inward current due to the synchronized oscillations in membrane potential of the surrounding cells. The membrane potential record of the impaled cell, obtained in current clamp mode, was used to estimate the behavior of the surrounding cells during voltage clamp, and the coupling conductance was calculated by dividing the magnitude of the current bursts by that of the voltage bursts. The histogram of coupling conductance magnitude from 26 cells was bimodal with peaks at 2.5 and 3.5 nS, indicating heterogeneity in extent of electrical communication within the islet of Langerhans. Gap junction conductance reversibly decreased when the temperature was lowered from 37 to 30°C and when the extracellular calcium concentration was raised from 2.56 to 7.56 mm. The coupling conductance decreased slightly during the active phase of the burst. Activation of adenylate cyclase with forskolin (10 μm) resulted in an increase in cell-to-cell electrical coupling. We conclude that β-cell gap junction conductance can be measured in situ under near physiological conditions. Furthermore, the magnitude and physiological regulation of β-cell gap junction conductance suggest that intercellular electrical communication plays an important role in the function of the endocrine pancreas.
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    Lysozyme acts as a chemorepellent and secretagogue in Paramecium by activating a novel receptor-operated Ca++ conductance (1995)
    Springer
    The journal of membrane biology 148 (1995), S. 13-25 
    Details
    ISSN: 1432-1424
    Keywords: Chemosensory transduction ; Ion channels ; Exocytosis ; Calcium ; Paramecium ; Receptors ; Lysozyme
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Using combined intracellular recordings and behavioral bioassays, it was found that lysozyme has two different effects in Paramecium, depending upon the concentrations used. At low concentrations (0.5 nm to 1.0 μm) it acts as an effective chemorepellent that causes reliable electrophysiological changes. Lysozyme-induced somatic depolarizations, isolated by blocking K+ channels with Cs-TEA, showed concentration dependencies that were well correlated with chemorepulsion. Ion dependency experiments showed that these were Ca++ based depolarizations. Addition of either Na+ or Mg++ improves chemorepulsion by providing additional depolarizations. Both the depolarizations and chemorepulsion were blocked by 10 μm neomycin, suggesting that the depolarization is necessary for this chemosensory transduction event. At higher concentrations (100 μm), lysozyme is a secretagogue. A transient inward current, recorded in Ca++ alone solutions with Cs-TEA present, was seen in response to high lysozyme concentrations. The amplitude of this inward current was well correlated with exocytosis. Addition of neomycin (1.0 mm) eliminated both the inward current and exocytosis, suggesting a causal relationship. Neither amiloride or W-7, compounds previously suggested to affect the electrophysiological responses to secretagogues, had any significant effects. The mucopolysaccharide hydrolysis activity of lysozyme was not required for any of these responses. We propose that Paramecium have a high affinity receptor on the body plasma membrane that responds to either lysozyme or a related compound to cause an increase in a novel body Ca++ conductance. This receptor-operated Ca++ conductance causes membrane depolarization and chemorepulsion at low concentrations and triggers a sufficient Ca++ influx at high concentrations to cause exocytosis.
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    Ion dynamics and its possible role during in vitro pollen germination and tube growth (1995)
    Springer
    Protoplasma 187 (1995), S. 155-167 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Channels ; Ion pumps ; Pollen ; Potassium ; Tip growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary One of the most interesting aspects of plant fertilization is the growth and orientation of the pollen tube from the stigma to the ovary. Considerable research has been carried out in this field but little is yet known about the mechanisms involved in the growth process. Recent research has been focused on the regulation of molecular events in order to discover the specific genes involved in tube growth. Important results in the biochemical and physiological aspects of molecular regulation have been reported. The following review attempts to cover these aspects. It is primarily based on talks presented by the authors at the 13th International Congress on Sexual Plant Reproduction and is mainly addressed to non-experts in the fields of electrophysiology and ion signalling. We aim to present a general overview of electrical currents, ion dynamics, and ion transporters in pollen, and their possible role during pollen tube germination and growth. Together with results on other tip-growing cells, a general model of pollen tube germination and growth as a self-organizing process is proposed.
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    Overproduction of Cdc24p (Cls4p), a guanine nucleotide-exchange factor toward Cdc42 GTPase, impairs initiation of budding inSaccharomyces cerevisiae (1995)
    Springer
    Protoplasma 189 (1995), S. 142-148 
    Details
    ISSN: 1615-6102
    Keywords: Cell polarity ; Budding yeast ; Calcium ; CLS4 gene ; CDC24 gene ; Overexpression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An entire coding region of theCDC24/CLS4 gene and its truncated derivatives were overexpressed in yeast cells under the control of theGAL1 promoter. Western blotting analysis of the yeast cell lysates showed that the CDC24/CLS4 protein (Cdc24p) was induced to reach its maximum level after 9 h incubation of the cells in galactose medium. Overexpression of Cdc24p within the cells caused the morphological change, accumulating large spherical unbudded cells which exhibited actin cytoskeleton disturbed, chitin delocalized on the cell surface, and cell viability decreased. Multiple nuclei were observed in these cells, indicating that only budding cycle but not nuclear division cycle is blocked by the overproduction of Cdc24p. In order to identify the region of Cdc24p responsible for the growth inhibition, several truncatedCDC24 genes were expressed. Surprisingly, overexpression of fragments either containing the C-terminal 76 amino acid residues or deleting the same region inhibited cellular growth. This suggests that Cdc24p contains multiple functional domains for its tasks, likely cooperating signals of bud positioning and bud timing.
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    Enhancement of paracellular drug transport across epithelia —in vitro andin vivo studies (1995)
    Springer
    Pharmacy world & science 17 (1995), S. 58-60 
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    ISSN: 1573-739X
    Keywords: Absorption, enhancement ; Biological transport ; Calcium ; Cells, cultured ; Epithelium permeability ; Osmotic challenge ; Salicylic acid ; Taurohydrofusidic acid ; Verapamil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Conclusion In conclusion the use of anin vitro cell culture system proved to be very valuable for (partly) elucidating the way of action of absorption-enhancing compounds and for the investigation of critical factors associated with absorption enhancement. The use of isolated cell culture systems like the Caco-2 cells can also have some drawbacks. Although this cell line is considered to be a very adequate model for intestinal epithelium, its properties might in some respects not be the same as those of normal cells, due to the fact that the cell line, originating from a carcinoma, consists of transformed cells. Direct extrapolation of potentially useful methods from thein vitro to thein vivo situation remains an important issue to consider as well and has been shown to be hazardous in the current investigations. A principal reason for this may be associated with the problem of maintaining conditionsin vivo very similar to those investigatedin vitro.
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    Membrane pores—From biology to track-etched membranes (1995)
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    Bioscience reports 15 (1995), S. 553-565 
    Details
    ISSN: 1573-4935
    Keywords: Calcium ; ion current ; membrane pore ; zinc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Flow of ions through narrow pores, either induced in biological membranes or created in synthetic membrane filters, exhibits, under appropriate conditions: 1) rapid switching of ion current between high and low conducting states; 2) selectivity between different ions; 3) inhibition by protons or divalent cations with an order of efficacy usually H+ 〉Zn2+〉Ca2+ 〉Mg2+. It seems reasonable to conclude that these common properties arise from a common cause-the nature of the flow of ions close to a charged surface.
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    Factors controlling somatic embryogenesis (1995)
    Springer
    Plant cell, tissue and organ culture 43 (1995), S. 147-154 
    Details
    ISSN: 1573-5044
    Keywords: Calcium ; callose ; Camellia japonica ; competence ; cutin ; somatic embryogenesis ; X-ray microanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Histological and ultrastructural, molecular and elemental distribution changes were investigated during the induction of direct somatic embryogenesis using theCamellia japonica leaf culture system. In this culture system, direct somatic embryogenesis is induced in a controlled way in a specific leaf region (leaf blade) within a leaf. Embryogenic and non-embryogenic leaf regions have characteristic energy-dispersive X-ray spectra already before induction. According to these results electron probe X-ray microanalysis (EPMA) can be a tool for early diagnosis of embryogenic competence. Histological studies showed that severe fluctuations in the number of calcium oxalate crystals and in starch accumulation occur after induction but only in induced tissues. Changes in the cell wall composition of competent cells occur shortly after the induction treatment. The induction of morphogenesis is linked to the appearance of callose covering the surface cells of induced leaves and calluses. A 2nd deposition of material (cutin) is necessary for normal somatic embryogenesis to occur. The involvement of lipid transfer proteins in the appearance of cutin in the embryogenic regions of the explant is suggested.
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    Intestinal calcium binding protein in uremia (1979)
    Springer
    Calcified tissue international 27 (1979), S. 205-210 
    Details
    ISSN: 1432-0827
    Keywords: Intestine ; Calcium ; Binding ; Protein ; Uremia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary In order to assess the usefulness of intestinal biopsies as indicators of end-organ responsiveness to vitamin D in uremic patients, calcium binding activity and calcium binding protein (CaBP) content were measured in intestinal biopsies from 12 uremic patients (glomerular filtration rate〈5.0 ml/min) and 12 adult controls. Values for both were found to vary with the site of biopsy, highest values being obtained in the duodenal bulb, with lower values distally. Values for activity correlated with values for CaBP content in both normals and uremics and no difference was observed between groups. Levels of calcium binding activity and content of CaBP did not correlate with serum immunoreactive parathormone levels, but were directly related to circulating 25-hydroxycholecalciferol (25-OHD) levels. The data show that intestinal CaBP is normal in activity, quantity, and affinity for calcium in malabsorbing uremic patients, and are consistent with the hypothesis that calcium malabsorption in uremia is unrelated to deficiency of intestinal calcium binding protein.
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    Bone fluoride concentrations associated with fluoridated drinking water (1979)
    Springer
    Calcified tissue international 27 (1979), S. 95-99 
    Details
    ISSN: 1432-0827
    Keywords: Bone ; Fluoride ; Analysis ; Food ; Age
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Recently published bone fluoride values from Iowa are very high compared to earlier reports, suggesting an increase in fluoride intake. Reanalysis of the Iowa specimens shows levels one-fourth those reported by the Iowa laboratory indicating an error in the original report. Seventeen bone specimens, collected from long-term residents of Rochester, New York, drinking 1 ppm F− water, had a mean value of 2085±270 ppm F− on an ashed-weight basis. This value is not significantly different from that predicted by the data of Zipkin et al. in 1958. These data, therefore, do not support the contention that there has been an increase in fluoride intake.
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    Precipitation of calcium phosphates from electrolyte solutions V. The influence of citrate ions (1979)
    Springer
    Calcified tissue international 28 (1979), S. 131-136 
    Details
    ISSN: 1432-0827
    Keywords: Calcium ; Phosphate ; Citrate ; Precipitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The influence of citrate ions on the precipitation of crystalline apatitic precipitates with low Ca/P molar ratios [octacalcium phosphate (OCP) and calcium-deficient apatites (DA) (system A)] and of the intercrystalline mixtures of calcium hydrogen phosphate dihydrate (DCPD) and DA (system B) was investigated. Samples were prepared by direct mixing of calcium chloride solutions (A, 6·10−3 mol dm−3; B, 1·10−1 mol dm−3) and sodium phosphate solutions (A, 6·10−3 mol dm−3; B, 2·10−2 mol dm−3) containing citrate (0–2·10−3 mol dm−3) and preadjusted to pH 7.4. In the presence of citrate ions: (a) crystal growth of OCP and DA was slowed down; (b) habit modification of DCPD crystals occurred; and (c) equilibration in intercrystalline mixtures of DCPD and DA's was slowed down. All phenomena were caused by surface adsorption of negatively charged ions, most probably CaC6H5O7-, which is the prevalent calcium citrate species under the given experimental conditions. Habit modification of DCPD was induced by preferential adsorption at the (001) crystal plane.
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    Comparative uptake of fluoride from sodium fluoride, ammonium fluoride, and barium fluoride in rat teeth when predominantly administered in the pre-eruptive stage of development (1979)
    Springer
    Calcified tissue international 27 (1979), S. 117-119 
    Details
    ISSN: 1432-0827
    Keywords: Pre-eruptive ; Systemic ; Deposition ; Absorbability ; Fluoride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A comparative study was undertaken which focused on the systemic uptake of sodium fluoride (NaF), ammonium fluoride (NH4F), and barium fluoride (BaF2) in rat pups. Two critical achievements made this comparative study possible: (a) the demonstration of significant increases in fluoride (F) uptake-deposition in the treatment group pups relative to control group rats as a result of stomach tube feeding; and (b) the demonstration of clear-cut differences in F concentration levels between the treatment groups as a result of this stomach tube-systemic uptake. Data were reliable and significant enough to suggest that, of the 3 compounds in question, NH4F is absorbed most successfully in a systemic fashion, whereas BaF2 is the least absorbed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441172
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  • 98
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    Disordered mineral metabolism produced by ketogenic diet therapy (1979)
    Springer
    Calcified tissue international 28 (1979), S. 17-22 
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    ISSN: 1432-0827
    Keywords: Anticonvulsant ; Ketogenic diet ; Calcium ; Vitamin D ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Vitamin D and mineral metabolism status was examined in five children maintained chronically on combined ketogenic diet-anticonvulsant drug therapy (KG), and the results compared to those obtained in 18 patients treated with anticonvulsant drugs alone (AD) and 15 normal controls. KG patients exhibited biochemical findings of vitamin D deficiency osteomalacia: decreased serum 25-hydroxyvitamin D (25OHD) and calcium concentrations, elevated serum alkaline phosphatase and parathyroid hormone concentrations, decreased urinary calcium and increased urinary hydroxyproline excretion, and decreased bone mass. Although the KG and AD groups demonstrated similar reductions in serum 25OHD concentration, the KG patients exhibited a significantly greater reduction in bone mass. In response to vitamin D supplementation (5000 IU/day), mean bone mass in the KG group increased by 8.1±0.9% (P〈0.001) over a 12-month period. These results suggest that ketogenic diet and anticonvulsant drug therapy have additive deleterious effects on bone mass and that these effects are partially reversible by vitamin D treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441213
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  • 99
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    Precipitation of calcium phosphates under conditions of double diffusion in collagen and gels of gelatin and agar (1979)
    Springer
    Calcified tissue international 27 (1979), S. 171-176 
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    ISSN: 1432-0827
    Keywords: Calcium ; Phosphate ; Precipitation ; Double diffusion ; Collagen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary One-dimensional double diffusion was applied to determine critical concentrations at which the precipitation of calcium phosphates occurs in reconstituted connective tissue collagen and agar gels at 37°C and in gelatin gels at 25°C. Experiments were performed in the presence of unbuffered 0.15 mol dm−3 NaCl, or 0.15 mol dm−3 NaCl-veronal adjusted to pH 7.4. It was found that critical concentrations of precipitation of both precipitating components, CaCl2 and phosphate buffer (pH 7.4), were equimolar and independent of the ratios of initial concentrations of the components. Critical concentrations of precipitation were not affected by the concentrations and kinds of gels used. The first-formed precipitates showed amorphous structure by X-ray diffraction analyses. Infrared (IR) spectra of the precipitates indicated CaHPO4 · H2O to be their predominant species. The molar Ca/P ratio obtained by chemical analyses was 1.08. This precipitate transformed in time into octacalcium phosphate. In all experiments, two very thin membranes of precipitate were formed in the gel column at the onset of precipitation simultaneously on both sides of the actual disc of precipitate. IR spectra and chemical analyses showed that both membranes were identical to the actual precipitation discs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441181
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  • 100
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    Factors affecting parathyroid hormone-induced hypophosphatemia and32P specific activity in thyroparathyroidectomized rats (1979)
    Springer
    Calcified tissue international 27 (1979), S. 239-246 
    Details
    ISSN: 1432-0827
    Keywords: Parathyroid hormone ; Calcium ; Plasma phosphate ; Bone phosphate ; Plasma32P ; Specific activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Plasma changes in calcium, phosphate, and their radionuclides were studied in thyroparathyroidectomized (TPTX) rats treated with parathyroid hormone (PTH) for 8 h, this treatment starting 10 h after injection of45Ca and32P. Prior to intravenous infusion or hourly injections of PTH (10 mU/g/h), rats were maintained in one of three ways: on an extended fast (24 h); on a partial fast (10 h); or provided with 10% glucose and 1% calcium lactate overnight as a substitution for solid food. The pattern of change for plasma calcium,45Ca, and45Ca specific activity (S.A.) produced by PTH was not affected by these dietary conditions. The changes in phosphate were as follows: During the experimental (8 h) period, the rate of loss of32P from plasma in control rats was proportional to the length of the fast. This suggests that32P was released into plasma during the experimental period proportional to the ready availability of soft tissue glucose. In rats on an extended fast, PTH was phosphaturic, hypophosphatemic, and increased the rate of loss of32P from plasma without affecting32P S.A. values. In rats fasted for only 10 h, PTH produced similar effects on plasma phosphate and plasma32P values, but also caused a significant fall in plasma32P S.A. After glucose and calcium lactate treatment, PTH-induced phosphaturia was temporarily lost and the marked hypophosphatemia was replaced with a slight hyperphosphatemia. Plasma32P values also rose slightly; therefore, no effect on32P S.A. was produced. It is concluded from these studies that as the result of the phosphaturia caused by PTH, the hypophosphatemia which is produced automatically changes the phosphate gradient between various body compartments, causing phosphate entry into plasma. The authors postulate that this phosphate entering plasma is withdrawn primarily from bone fluid and bone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441192
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