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  • calcium  (147)
  • Springer  (147)
  • 2020-2024
  • 2015-2019
  • 1985-1989  (147)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Dystrophin and the integrity of the sarcolemma in Duchenne muscular dystrophy (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 175-177 
    Details
    ISSN: 1420-9071
    Keywords: Dystrophin ; calcium ; skeletal muscle ; muscular dystrophy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary It is suggested that in Duchenne muscular dystrophy the absence of dystrophin, which is probably a cytoskeletal protein underlying the sarcolemma, causes changes in stretch-activated cation channels rather than direct mechanical tearing of the surface membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01954866
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  • 2
    Electronic Resource
    Electronic Resource
    Cerebrovascular autoregulation is resistant to calcium channel blockade with nimodipine (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 305-306 
    Details
    ISSN: 1420-9071
    Keywords: Baboon ; 133xenon ; cerebral blood flow ; cerebrovascular resistance ; autoregulation ; nimodipine ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In normal baboons cerebrovascular resistance changed along with blood pressure to maintain blood flow constant. This ‘autoregulation’ was not significantly altered in animals treated with a dose of the calcium channel blocker nimodipine causing selective cerebral vasodilation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01951818
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  • 3
    Electronic Resource
    Electronic Resource
    Morphological evidence for calcium storage in the chromatoid body of rat spermatids (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 377-378 
    Details
    ISSN: 1420-9071
    Keywords: Chromatoid body ; spermatids ; calcium ; microtubules ; morphology ; pyroantimonate ; rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Morphological evidence for probable Ca2+ storage in the vesicular elements of the rat spermatid chromatoid body is documented using the K-pyroantimonate method, combined with EDTA chelation. Some vesicles are related to the microtubules associated with the chromatoid body. A possible involvement of Ca2+ in the intracellular movement and/or structural integrity of the chromatoid body is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01957484
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  • 4
    Electronic Resource
    Electronic Resource
    Arachidonic acid mobilization in platelets: The possible role of protein kinase C and G-proteins (1988)
    Springer
    Cellular and molecular life sciences 44 (1988), S. 101-104 
    Details
    ISSN: 1420-9071
    Keywords: Platelets ; calcium ; phospholipase A2 ; G-proteins ; arachidonic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A major route for the release of arachidonic acid from platelet phospholipids appears to be catalyzed by a phospholipase A2 that can be stimulated by a rise of cytosolic Ca2+. This paper discusses certain other mechanisms for regulation of this process. Release of arachidonic acid by calcium ionophores is potentiated by pretreatment with stimulators of protein kinase C; e.g. diglyceride, phorbol esters and the terpene diester mezerein. This effect appears to be coincident with phosphorylation of a certain group of proteins (not 47 KDa protein), and is sensitive to depletion of ATP, activation of Ca2+ dependent phosphatase, and the kinase C inhibitor H-7, but is unaffected by Na+/H+ exchange inhibitors. Recent results in other cell types strongly indicate that phospholipase A2 is also directly under control of certain GTP-binding proteins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952189
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  • 5
    Electronic Resource
    Electronic Resource
    Increase in cellular cyclic GMP level by potassium stimulation and its relation to ciliary orientation inParamecium (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 62-64 
    Details
    ISSN: 1420-9071
    Keywords: Cyclic GMP ; calcium ; Paramecium ; triton-extracted model ; ciliary reversal ; excitable membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Physiological roles of cyclic GMP in the control of ciliary movement inParamecium caudatum were investigated. We found that 1) an increase in cellular cyclic GMP level was observed in association with recovery from the ciliary reversal produced by K stimulation, and 2) the presence of cyclic GMP inhibited the Ca-induced ciliary reversal in triton-extracted models. These results suggest that cyclic GMP plays a key role in the control of the Ca-mediated ciliary reversal mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01975897
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  • 6
    Electronic Resource
    Electronic Resource
    Calcitonin-like peptide in the shrimpPalaemon serratus (Crustacea, Decapoda) during the intermolt cycle (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 419-420 
    Details
    ISSN: 1420-9071
    Keywords: Crustacean ; calcitonin ; radioimmunoassay ; calcium ; molt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A molecule immunologically related to salmon calcitonin has been detected in the hemolymph of the shrimpPalaemon serratus. Its concentration varies inversely with the calcium level during the molt cycle; a maximum (14 ng/ml) is found in the post-molt stage and a minimum (0.5 ng/ml) during the premolt stage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02118638
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  • 7
    Electronic Resource
    Electronic Resource
    Ionic currents in morphogenesis (1988)
    Springer
    Cellular and molecular life sciences 44 (1988), S. 657-666 
    Details
    ISSN: 1420-9071
    Keywords: Ionic currents ; vibrating probe ; membrane potential ; fucoid egg polarization ; animal-vegetal polarity ; polarization ; voltage gradients ; calcium ; vesicle secretion ; Achlya ; oocytes ; insect follicle ; insect ovariole ; polarized transport ; egg activation ; mouse blastomere ; epithelial morphogenesis ; limb bud
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Morphogenetic fields must be generated by mechanisms based on known physical forces which include gravitational forces, mechanical forces, electrical forces, or some combination of these. While it is unrealistic to expect a single force, such as a voltage gradient, to be the sole cause of a morphogenetic event, spatial and temporal information about the electrical fields and ion concentration gradients in and around a cell or embryo undergoing morphogenesis can take us one step further toward understanding the entire morphogenetic mechanism. This is especially true because one of the handful of identified morphogens is Ca2+, an ion that will not only generate a current as it moves, but which is known to directly influence the plasma membrane's permeability to other ions, leading to other transcellular currents. It would be expected that movements of this morphogen across the plasma membrane might generate ionic currents and gradients of both electrical potential and intracellular concentration. Such ionic currents have been found to be integral components of the morphogenetic mechanism in some cases and only secondary components in other cases. My goal in this review is to discuss examples of both of these levels of involvement that have resulted from investigations conducted during the past several years, and to point to areas that are ripe for future investigation. This will include the history and theory of ionic current measurements, and a discussion of examples in both plant and animal systems in which ionic currents and intracellular concentration gradients are integral components of morphogenesis as well as cases in which they play only a secondary role. By far the strongest cases for a direct role of ionic currents in morphogenesis is the polarizing fucoid egg where the current is carried in part by Ca2+ and generates an intracellular concentration gradient of this ion that orients the outgrowth, and the insect follicle in which an intracellular voltage gradient is responsible for the polarized transport from nurse cell to oocyte. However, in most of the systems studied, the experiments to determine if the observed ionic currents are directly involved in the morphogenetic mechanism are yet to be done. Our experience with the fucoid egg and the fungal hypha ofAchlya suggest that it is the change in the intracellular ion concentration resulting from the ionic current that is critical for morphogenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01941026
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  • 8
    Electronic Resource
    Electronic Resource
    Oviposition behaviour of Dacus tryoni: The effects of some sugars and salts (1985)
    Springer
    Entomologia experimentalis et applicata 39 (1985), S. 61-71 
    Details
    ISSN: 1570-7458
    Keywords: Dacus tryoni ; Tephritidae ; Diptera ; fruit flies ; oviposition ; egg laying ; behaviour ; taste receptors ; chemoreceptors ; stimulant ; deterrent ; fructose ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Résumé Des mouches fruitières gravides du Queensland (Dacus tryoni), confinées au laboratoire dans des chambres d'oviposition sont stimulées par la présence de β-D(-)fructose, à pondre significativement plus d'oeufs dans un substrat gélosé. Ce composé est un véritable stimulant d'oviposition, accroissant le nombre d'oeufs déposés par mouche, plutôt que simplement localisant l'oviposition dans les substrats le contenant. Le fructose est effectif seulement lorsqu'il est accessible aux récepteurs gustatifs tarsaux et labelliaux et, apparement, agit en stimulant de plus fréquentes insertions de l'ovipositeur dans le substrat; le contact du fructose avec uniquement l'ovipositeur inséré, n'accroît pas l'oviposition. Le seuil de concentration pour obtenir une stimulation par le fructose est de 4 mM; la résponse maximale se produit à 50 mM et au delà, auxquelles concentrations l'oviposition est augmentée d'un facteur 6 par rapport au témoin, qu'il y ait ou non possibilité de choix de substrat. Le sucrose (testé à 100 et 1 000 mM) et le D-glucose (testé à 100 et 500 mM) ne stimulent pas l'oviposition chez D. tryoni. Le fructose favorise fortement l'oviposition grâce aux trous existants dans une surface impénétrable, et dans les conditions naturelles, D. tryoni l'utilise probablement comme un marqueur pour localiser les ruptures dans la peau des fruits, où l'insertion est plus facile. La présence de chlorure de calcium molaire dans la gélose fructose inhibe fortement l'oviposition, même lorsqu'il est inaccessible aux récepteurs gustatifs tarsaux et labelliaux. Le chlorure de sodium molaire n'est pas inhibiteur. Les ions calciums déploient apparemment leur effet inhibiteur par l'intermédiaire de récepteurs gustatifs localisés sur l'ovipositeur.
    Notes: Abstract Gravid Queensland fruit flies (Dacus tryoni) are stimulated by the presence of β-D(-) fructose to lay significantly more eggs in an agar substrate. Fructose is only effective when accessible to the tarsal and/or labellar gustatory sensilla; it greatly increases oviposition through holes in an impenetrable membrane. Threshold for the fructose effect is 4 mM, maximal response being at 50 mM and above. Sucrose and glucose are not oviposition stimulants for D. tryoni. In the field situation D. tryoni probably uses fructose as a marker to locate breaks in the skin of ripe fruit, where insertion of the ovipositor is easier. The flies are deterred from ovipositing in fructose agar by the presence of molar calcium chloride, even when this is inaccessible to the tarsal and labellar gustatory sensilla. Molar sodium chloride is not inhibitory. Calcium ions apparently exert their inhibitory effect via gustatory sensilla located on the ovipositor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00338525
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  • 9
    Electronic Resource
    Electronic Resource
    Heterogeneity of calcium compartmentation: Electron probe analysis of renal tubules (1986)
    Springer
    The journal of membrane biology 94 (1986), S. 191-196 
    Details
    ISSN: 1432-1424
    Keywords: calcium ; kidney proximal tubule ; electron probe ; X-ray microanalysis ; mitochondria ; cytoplasmic calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The objective of this study has been to determine the intracellular localization of calcium in cryofixed, cryosectioned suspensions of kidney proximal tubules using quantitative electron probe X-ray microanalysis. Two populations of cells have been identified: 1) „Viable” cells, representing the majority of cells probed, are defined by their relatively normal K/Na concentration ratio of ∼4∶1. Their measured Ca content is 4.1±1.4 (sem) mmol/kg dry wt in the cytoplasm and 3.1 ± 1.1 mmol/kg dry wt in the mitochondria, or an average cell calcium content of ∼3.8 mmol/kg dry wt. 2) “Nonviable” cells, defined by the presence of dense inclusions in their mitochondria and a K/Na concentration ratio of ∼1. The Ca content is 15±2 mmol/kg dry wt in the cytoplasm and 685±139 mmol/kg dry wt in the mitochondria of such cells. Assuming 25 to 30% of the cell volume is mitochondrial, the overall calcium content of such nonviable cells is ∼ 210 mmol/kg dry wt. The presence of these inclusions in 4 to 5% of the cells would account for the average total Ca content measured in perchloric acid extracts of isolated proximal tubule suspensions (≈ 18 nmol/mg protein or 12.6 mmol/kg dry wt). Whole kidney tissues display a large variability in toal Ca content (4.5 to 18 nmol/mg protein, or 3.4 to 13.5 mmol/kg dry wt), which could be accounted for by inclusion in 0 to 4% of the cells. The electron probe X-ray microanalysis (EPXMA) data conclusively demonstrate that thein situ mitochondrial Ca content of viable cells from the kidney, proximal tubule is low and support the idea that mitochondrial Ca may regulate dehydrogenase activity but probably does not normally control cytosolic free Ca.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871198
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  • 10
    Electronic Resource
    Electronic Resource
    Calcium-induced fusion of didodecylphosphate vesicles: The lamellar to hexagonal II (HII) phase transition (1987)
    Springer
    The journal of membrane biology 95 (1987), S. 255-263 
    Details
    ISSN: 1432-1424
    Keywords: didodecylphosphate ; calcium ; membrane fusion ; lamellar phase ; hexagonal phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Electron microscopic techniques have been employed to investigate the ability of didodecylphosphate vesicles (diameter approx. 900 Å) to fuse in the presence of Ca2+. As revealed by negative staining, Ca2+ induces extensive fusion and large vesicles with diameters up to 7000 Å are formed. In a processsecondary to fusion, the fused vesicles display a tendency to flatten and are subsequently transformed into extended tubular structures. Freeze-fracture electron microscopy, in conjunction with31P NMR and selected area electron diffraction measurements indicate that the tubes are packed in a hexagonal (HII) array and that the amphiphiles are converted from the lamellar to the hexagonal HII phase. The relationship between membrane fusion and the lamellar-to-hexagonal phase transition is discussed in terms of formation and abundance of transiently stable inverted micellar intermediates at contact regions between two interacting membranes. A model for the conversion of the (vesicular) lamellar into the (tubular) hexagonal HII phase is presented, taking into account the molecular shape of the amphiphile. The relevance of using simple synthetic amphiphiles as models for phospholipid bilayers and complex biomembrane behavior is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869487
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  • 11
    Electronic Resource
    Electronic Resource
    Calcium transport affinity, ion competition and cholera toxin effects on cytosolic Ca concentration (1987)
    Springer
    The journal of membrane biology 96 (1987), S. 243-249 
    Details
    ISSN: 1432-1424
    Keywords: cholera toxin ; ionophore ; calcium ; brush-border membrane vesicles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The physiological relevance of an apparent ionophore activity of cholera toxin towards Ca2+ has been examined in several different systems designed to measure affinity, specificity, rates of ion transfer, and effects on intracellular ion concentrations. Half-maximal transfer rates across porcine jejunal brush-border vesicles were obtained at a concentration of 0.20 μM Ca2+. When examined in the presence of competing ions the transfer process was blocked by very low concentrations of La3+ or Cd2+. Sr2+, Ba2+ and Mg2+ were relatively inefficient competitors for Ca2+ transport mediated by cholera toxin. The relative affinities observed would be compatible with a selectivity for Ca2+ transfer at physiological ion concentrations, as well as an inhibition of this ionophore activity by recognized antagonists of cholera toxin such as lanthanum ions. Entry rates of Ca2+ into brush-border vesicles exposed to cholera toxin were large enough to accelerate the collapse of a Ca2+ gradient generated by endogenous Ca, Mg-ATPase activity. The treatment of isolated jejunal enterocytes with cholera toxin caused a significant elevation in cytosolic Ca2+ concentrations as measured by Quin-2 fluorescence. This effect was specifically prevented by prior exposure of the cholera toxin to excess ganglioside GM1. We conclude that cholera toxin has many of the properties required for promoting transmembranes Ca2+ movement in membrane vesicles and appears to be an effective Ca2+ ionophore in isolated mammalian cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869306
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  • 12
    Electronic Resource
    Electronic Resource
    Arsenazo, 2-(4-arsonophenyl(azo-7-(4-antipyril)azo-1,8-dihydroxy-3,6-naphtalene disulphonic acid as reagent for calcium ions. New parameters for metallochromic indicator characterization (1986)
    Springer
    Microchimica acta 88 (1986), S. 73-85 
    Details
    ISSN: 1436-5073
    Keywords: arsenazo ; calcium ; titration ; tristimulus-colorimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ca(II) ions react with arsenazo, 2-(4-arsonophenyl)-azo-7-(4-antipyril)azo-l,8-dihydroxy-3,5-naphtalene disulphonic acid, at pH 10.0 to produce a blue complex, with stoichiometry 1∶1, and stability constant of 6.64×105. Its molar absorptivity is 3.78×1041·mol−1 cm−1. This reagent has been used as metallochromic indicator in the complexometric titration of Ca. Its colour transition has been specified by tristimulus colourimetry. New parameters are defined and compared to Ringbom's parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01196689
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  • 13
    Electronic Resource
    Electronic Resource
    Involvement of a Ca2+-calmodulin interaction in the yeast-mycelial (Y-M) transition of Candida albicans (1989)
    Springer
    Mycopathologia 108 (1989), S. 47-54 
    Details
    ISSN: 1573-0832
    Keywords: Candida albicans ; dimorphism ; yeast-mycelium transition ; calcium ; calmodulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A yeast-mycelium (Y-M) transition of Candida albicans (3153A) was induced by 1.5 mM CaCl2 · 2H2O in defined liquid medium, pH 7, at 25 °C. Germ tube formation was detected after approximately 8 h and peaks of maximum germination occurred at approximately 20 h in all experimental treatments. Non-toxic concentrations of the calmodulin inhibitor R24571 almost completely suppressed germ tube formation whereas trifluoperazine (TFP) and the Ca2+ ionophore A23187 were only about half as effective. Further Ca2+ addition failed to reverse the inhibitory effect of R24571 and induced only about 10% of the cells inhibited by TFP or A23187 to germinate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00436783
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  • 14
    Electronic Resource
    Electronic Resource
    Guayule seedling response to nitrogen fertilizers (1987)
    Springer
    Nutrient cycling in agroecosystems 11 (1987), S. 113-121 
    Details
    ISSN: 1573-0867
    Keywords: ammonium sulfate ; urea ; calcium nitrate ; nitrogen-calcium interaction ; leaching ; subirrigation ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Slow growth and high seedling mortality limit direct seeding establishment of guayule (Parthenium argentatum G.). This study was conducted to assess seedling growth enhancement by the addition of different rates and forms of N fertilizers and Ca salts. Experiments were conducted in a greenhouse with cultivar 593 under both surface and subirrigated conditions using water low in salts (salinity of 0.8 dSm−1, SAR of 5.0 and 10 mg Ca L−1). Under surface-irrigated conditions, seedling height and fresh plant weight increased with N application to the irrigation water to 70 mg L−1. The best seedling growth was observed when (NH4)2SO4 was added in combination with CaCl2 or CaSO4. Progressively less growth was observed by addition of (NH4)2SO4 alone, CO(NH2)2 plus CaSO4, CO(NH2)2 alone and Ca(NO3)2. When seedlings were subirrigated, however, the best growth was observed with Ca(NO3)2. Intermediate growth was obtained with (NH4)2SO4 plus CaSO4 and lowest growth rates with (NH4)2SO4 alone. These differential responses may be explained by the differences in leaching and volatile characteristics of the N forms. Growth enhancement from N and Ca additions increased with time with significant increases 45 days after seeding. Nitrogen application with Ca may be effective amendment in promoting subsequent growth of direct seeded guayule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01051055
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  • 15
    Electronic Resource
    Electronic Resource
    The variation of element contents in triticale during vegetative growth (1987)
    Springer
    Nutrient cycling in agroecosystems 13 (1987), S. 155-159 
    Details
    ISSN: 1573-0867
    Keywords: triticale ; contents of nitrogen ; phosphorus ; potassium ; calcium ; magnesium ; trace elements ; heavy metals ; stage of growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Description / Table of Contents: Zusammenfassung Es wurden die Schwankungen in den Konzentration von N, P, K, Ca, Mg, Fe, Mn, Zn, Cu, B, Ba, Be, Bi, Sn, Sr, Sb, Ti, Te, V, Se, As und Hg in Triticale unter Feldbedingungen untersucht. Von der Bestockung bis zur Vollreife wurden alle 10 Tage von je 0.5 m2 pro Parzelle Pflanzenproben genommen. In allgemeinen haben die Konzentrationen von Frühjar bis zur Ernte abgenommen. Der elementengehalt in Triticale war demjenigen der übrigen Getreidearten verschieden, aber der Trend der Änderungen war ähnlich.
    Notes: Abstract The variation of N, P, K, Ca, Mg, Fe, Mn, Zn, Cu, B, Ba, Be, Bi, Sn, Sr, Sb, Ti, Te, V, Se, As and Hg concentrations was studied under field conditions in triticale. The samples were collected every 10 days from tillering to full ripening stage using plant material from 0.5 m2 per plot. The concentrations generally decreased from early growth to harvest. The elemental concentrations in triticale differed from the other cereals, but the variation's trend was similar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01064828
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  • 16
    Electronic Resource
    Electronic Resource
    Effect of cation exchange on the distribution and movement of cations in soils with variable charge. I. Effect of lime on potassium and magnesium exchange equilibria (1988)
    Springer
    Nutrient cycling in agroecosystems 17 (1988), S. 21-30 
    Details
    ISSN: 1573-0867
    Keywords: Potassium ; magnesium ; calcium ; aluminium ; exchange coefficient ; equilibrium activity ratio ; organic matter ; bonding strength
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The influence of Ca(OH)2 on K and Mg exchange equilibria in three New Zealand soils was studied. Calcium hydroxide was mixed with each soil to raise the pH to about 6 or 7. For each Ca(OH)2 treatment, K and Mg exchange isotherms were determined, from which the equilibrium activity ratios were derived. Exchange coefficients and solution activity ratios were calculated according to the Gapon convention. The addition of Ca(OH)2 produced varying effects in the Gapon exchange coefficient for both K and Mg. The magnitude and direction of change in the exchange coefficient were related to the cation initially dominating the exchange sites, rate of Ca(OH)2 addition, soil colloids contributing to the CEC and specific interactions of Ca with these soil colloids. Addition of Ca(OH)2 reduced the equilibrium activity ratio of all soils. Changes in the bonding strength of K and Mg with increasing CEC were suggested as a possible mechanism for this decrease.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01050454
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  • 17
    Electronic Resource
    Electronic Resource
    Cultivation, frozen storage, and clonal growth of normal human epidermal keratinocytes in serum-free media (1985)
    Springer
    Methods in cell science 9 (1985), S. 83-93 
    Details
    ISSN: 1573-0603
    Keywords: keratinocytes ; human ; epidermis ; serum-free ; calcium ; differentiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Methods are described for serum-free culture of human epidermal keratinocytes derived from neonatal foreskin tissue. Cultures are initiated, stored frozen, and returned to active growth, all with bovine pituitary extract as the only undefined supplement. Clonal growth assays are then performed in a biochemically defined medium. The degree of stratification and differentiation in the defined medium (and also with pituitary extract) is controlled by the extracellular calcium ion concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01797779
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  • 18
    Electronic Resource
    Electronic Resource
    Release of calcitonin gene-related peptide from a human medullary carcinoma of the thyroid in vitro (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 829-830 
    Details
    ISSN: 1420-9071
    Keywords: Calcitonin gene-related peptide ; calcitonin ; calcium ; perifusion ; medullary carcinoma of thyroid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The secretion of human calcitonin gene-related peptide was examined in perifusates of medullary carcinoma of the thyroid with a sensitive radioreceptor assay. Calcitonin gene-related peptide was released after the addition of calcium (25–100 mM), in a dose-dependent manner. The results indicate that human medullary carcinomas of the thyroid secrete the calcitonin gene-related peptide as well as calcitonin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01941541
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  • 19
    Electronic Resource
    Electronic Resource
    Modulation of calcium sensitivity in guinea pig taenia coli: skinned fiber studies (1985)
    Springer
    Cellular and molecular life sciences 41 (1985), S. 997-1001 
    Details
    ISSN: 1420-9071
    Keywords: Myosin light chain kinase ; calcium ; c-AMP ; calmodulin ; smooth muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952120
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  • 20
    Electronic Resource
    Electronic Resource
    Failure of calcium to stimulate Na, K-ATPase in the presence of EDTA (1985)
    Springer
    Cellular and molecular life sciences 41 (1985), S. 1048-1051 
    Details
    ISSN: 1420-9071
    Keywords: Na, K-ATPase ; calcium ; calmodulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effect of calcium on Na, K-ATPase activity of rat brain homogenates and its modification by the chelating agent EDTA has been investigated. In the absence of EDTA, free calcium (approximately 10−6mol/l) stimulates Na,K-ATPase activity; in the presence of EDTA the same concentration of free calcium is without effect on the enzyme. In the absence of EDTA the stimulation by calcium of Na,-K-ATPase activity is enhanced by the additional presence of calmodulin but in the presence of EDTA, even when calmodulin is added to excess, calcium still fails to stimulate the enzyme. The possibility that EDTA interferes with an interaction between a calcium-calmodulin complex and Na,K-ATPase is discussed.
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    Mechanical and biochemical characterization of the contraction elicited by a calcium-independent myosin light chain kinase in chemically skinned smooth muscle (1985)
    Springer
    Cellular and molecular life sciences 41 (1985), S. 1002-1006 
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    ISSN: 1420-9071
    Keywords: Smooth muscle ; calcium ; myosin light chain kinase ; regulation of contraction ; ATPase ; mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The contraction induced by a Ca2+-independent myosin light chain kinase (MLCK-) was characterized in terms of isometric force (Fo), immediate elastic recoil (SE), unloaded shortening velocity (Vus), shortening under a constant load and ATPase activity of chemically skinned smooth muscle preparations. These parameters were compared to those measured in a Ca2+-induced contraction to assess the nature of cross bridge interaction in the MLCK-induced contraction. Fo developed in chicken gizzard fibers as well as SE were similar in contractions elicited by either agent. Vus in the contraction induced by MLCK-(0.36 mg/ml) was similar though averaged 39.3±8.9% less than Vus induced by Ca2+ (1.6x10−6M) in the control fibers. Addition of Ca2+ (1.6x10−6M) to a contraction induced by MLCK-resulted in small increases in both Fo and Vus. Shortening under a constant load was similar for both types of contractions. The contraction induced by MLCK-was accompanied by an increased rate of ATP hydrolysis. The MLCK-induced contraction is thus kinetically similar though not identical to a contraction induced by Ca2+. We conclude that with respect to actin-myosin interaction, MLCK- and Ca2+-induced contractions are similar.
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    Energetics and regulation of crossbridge states in mammalian smooth muscle (1985)
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    Cellular and molecular life sciences 41 (1985), S. 1020-1025 
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    ISSN: 1420-9071
    Keywords: Smooth muscle energetics ; light chain phosphorylation ; crossbridges ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Conclusion On the basis of measurements of the high energy phosphate usage associated with different mechanical states, as well as the degree of myosin light chain phosphorylation and mechanical properties, information has been gained concerning the existence and regulation of different crossbridge states in smooth muscle. Although incomplete, a general operational scheme is shown in figure 5. At very low intracellular calcium concentrations, actin and myosin are dissociated, as shown by a loss of resistance to stretch in resting muscles. At somewhat higher intracellular calcium concentrations in atonic, resting muscles, crossbridges can attach and be manifest mechanically as an increased resistance to stretch without ATP-driven crossbridge cycling and active force production. When the muscle is activated, intracellular calcium increases further, the light chains of myosin are phosphorylated through the calcium-calmodulin activation of myosin light chain kinase, actin-activated myosin ATPase activity increases and crossbridges cycle. Calcium also appears to modulate the ATPase activity and the rate of cycling of the phosphorylated crossbridge. The crossbridge cycling rate is highest during force development and slows with time as maximum isometric force is maintained reflecting a change in the rate at which phosphorylated crossbridges cycle. This may result from a decrease in the intracellular free calcium concentration with continued stimulation. During relaxation, the intracellular calcium concentration decreases, there is net dephosphorylation of the myosin light chains, the rate at which phosphorylated crossbridges cycle slows further with a gradual return to the attached, but non-cycling state or the detached state.
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    Effects of water acidification on the distribution pattern and the reproductive success of amphibians (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 495-503 
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    ISSN: 1420-9071
    Keywords: Acidication ; pH ; calcium ; (heavy) metals ; ammonium ; amphibians ; development of eggs ; hatching percentage ; mortality of larvae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Nine amphibian species were encountered in poorly buffered waters of The Netherlands (alkalinity ≦1 meq·l−1). These soft water systems are highly sensitive to acidifying precipitation. The number of species as well as the percentage of waters which harbour amphibian populations are strongly reduced in the extremely acid pH-class $$(\bar pH〈 4.0)$$ . The reproductive success of amphibians is negatively affected by low pH. The eggs become heavily infested with fungi (Saprolegniaceae). In acidifying systems many physico-chemical parameters are significantly correlated with the pH of the water. Strongly acidified waters are characterized by low alkalinity, conductivity and ionic content but high acidity and high concentrations of (heavy) metals and ammonium and a high relative sulphate concentration. Culture experiments with eggs and larvae ofRana arvalis. Rana ‘esculenta’, Rana temporaria andBufo bufo show that apart from the pH, elevated aluminium, cadmium and ammonium contents may also affect the reproductive success of amphibians.
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    Development of the myocardial contractile system (1988)
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    Cellular and molecular life sciences 44 (1988), S. 936-944 
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    ISSN: 1420-9071
    Keywords: Contractile system ; fetus ; premature myocardium ; calcium ; sarcoplasmic reticulum ; contractile protein ; sarcolemma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Recent studies regarding developmental changes in the myocardial contractile system from fetal, newborn, and adult animals are reviewed. From the data obtained so far, we conclude that in the early fetus myocardial contraction is mainly dependent on Ca which enters via the sarcolemma. Ca release from the sarcoplasmic reticulum is minimal. The role of the sarcoplasmic reticulum as a source of contractile Ca increases and the role of Ca influx across the sarcolemma in contractile system decreases with development.
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    The effects of acid deposition on benthic animals in lakes and streams (1986)
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    Cellular and molecular life sciences 42 (1986), S. 471-486 
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    ISSN: 1420-9071
    Keywords: Acidification ; benthic animals ; calcium ; invertebrates ; lakes ; pH ; streams ; fresh water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF01946685
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    Biological effects of lithium: Experimental analysis in plant cytokinesis (1987)
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    Cellular and molecular life sciences 43 (1987), S. 1025-1027 
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    ISSN: 1420-9071
    Keywords: Plant cytokinesis ; lithium ; caffeine ; calcium ; magnesium ; sodium and potassium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The biological effects of lithium ions have been studied, using plant cytokinesis in onion root meristems as the experimental model. Lithium induces binucleate cells by inhibiting cell plate formation. Moreover, lithium and caffeine have additive effects on the induction of binucleate cells. Na+, K+, Ca++ and Mg++ antagonize lithium-induced inhibition of cytokinesis.
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    Effects of calcium on the gramicidin A single channel in phosphatidylserine membranes (1987)
    Springer
    European biophysics journal 14 (1987), S. 369-374 
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    ISSN: 1432-1017
    Keywords: Single-channels ; model membranes ; gramicidin ; surface potential ; phosphatidylserine ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract In phosphatidylserine membranes the decrease in the conductance of the gramicidin A single channel caused by calcium is attributed to a reduction of surface potential and to a direct blocking of the pore (Apell et al. 1979). The aim of this paper is to make a, quantitative evaluation of these two effects. We recorded the conductance of gramicidin single channels in 100 mM KCl in the presence of different amounts of CaCl2, MgCl2 or TEACl. The ionic activities at the channel mouth were calculated using the Gouy-Chapman-Stern theory. Our experiments showed that even when the K+ activity at the channel mouth was estimated to be the same, the single channel conductance was lower if divalent cations were present. This effect is attributed to a blocking action of these ions.
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    Neutron scattering by calf lens cytoplasm (1987)
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    European biophysics journal 14 (1987), S. 441-447 
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    ISSN: 1432-1017
    Keywords: Neutron scattering ; lens ; cataract ; calcium ; cold cataract
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Small angle neutron scattering (SANS) was used to compare two models of cataracts: the cold cataract induced in the lens nucleus cytoplasm by lowering the temperature and the opacification induced by calcium in the lens cortex cytoplasm. In both cases opacified cytoplasms display additional scattering at low angles as compared to their clear controls. An analysis of this additional scattering provides quantitative information concerning the size distribution, the number and contrast of the scatterers responsible for lens opacification. The scatterers of cold cataract and of calcium—induced opacification not only have, as shown elsewhere, a different composition but are also found to display completely different sizes (in the thousand Å range for cold-cataract, in the hundred Å range for calcium—induced opacification). These results illustrate the diversity of scatterer types which are able to cause comparable lens opacities.
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    Calcium movements during each heart beat (1989)
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    Molecular and cellular biochemistry 89 (1989), S. 103-108 
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    ISSN: 1573-4919
    Keywords: heart ; relaxation ; calcium ; sodium-calcium exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Transsarcolemmal calcium movements are closely related to force generation in the heart. It is important to understand the transport pathways that control these movements of calcium across the sarcolemmal membrane. In the normal, beating heart, sodium-calcium exchange appears to be an important mechanism for the extrusion of calcium from the cell. The kinetics of this exchange are dependent upon the characteristics of the cell action potential. Calcium efflux via sodium-calcium exchange may be sufficient to balance calcium entry through calcium channels during the action potential.
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    Sodium-calcium exchange in mammalian heart: current-voltage relation and intracellular calcium concentration (1989)
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 97-102 
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    ISSN: 1573-4919
    Keywords: calcium ; sodium ; fura-2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Membrane currents and changes in intracellular calcium ion concentration ([Ca2+]i) have been recorded that can be attributed to the operation of an electrogenic, voltage-dependent sodium-calcium (Na-Ca) exchanger in mammalian heart cells. Single guinea-pig ventricular myocytes under voltage clamp were perfused internally with the fluorescent Ca2+-indicator, fura-2, and changes in [Ca2+]i and membrane current that resulted from Na-Ca exchange were isolated through the use of various organic channel blockers (verapamil, TTX), impermeant ions (Cs+, Ni2+), and inhibitors of sarcoplasmic reticulum (ryanodine). The I-V relation of Na-Ca exchange was obtained from the Ni2+-sensitive current elicited by ramp repolarization from +90 mV to −80 mV. Ramps were sufficiently rapid that little change in [Ca2+]i occured during the ramp. The (constant) [Ca2+]i during the ramp was varied over the range 100 nM to 1000 nM by varying the amplitude and duration of a pre-pulse to the ramp. The reversal potential of the Ni2+-sensitive ramp current varied linearly with 1n([Ca2+])i. The I-V relations at different [Ca2+]i over the range −60 mV to +140 mV were in reasonable accord with the predictions of a simple, simultaneous scheme of Na-Ca exchange, on the basis that only [Ca2+]i had changed. The relationship between [Ca2+]i and current at a constant membrane voltage was also in accord with this scheme. We suggest that Ca2+-fluxes through the exchanger during the cardiac action potential can be understood quantitatively by considering the binding of Ca2+ to the exchanger during the [Ca2+]i-transient and the effects of membrane voltage on the exchanger.
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    Appraisal of the physiological relevance of two hypotheses for the mechanism of calcium release from the mammalian cardiac sarcoplasmic reticulum: calcium-induced release versus charge-coupled release (1989)
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 135-140 
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    ISSN: 1573-4919
    Keywords: calcium ; heart ; sarcoplasmic reticulum ; excitation-contraction coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Recent studies correlating the calcium current with, respectively, the clamp-imposed voltage and the calcium current in intact isolated mammalian cardiac myocytes are reviewed. The major findings are the following: [1] With the exception of one group, all investigators agree that a calcium transient is never observed in the absence of a calcium current. In addition, there is a good correlation between voltage dependence of the calcium current and that of the calcium transient, although this correlation may vary among the cardiac tissues from different animal species. [2] Repolarization clamp pulses from highly positive potentials produce a ‘tail current’ which is associated with a ‘tail calcium transient’. [3] The calcium transient is inhibited when the calcium current is blocked by calcium deprivation or substitution, or by the addition of calcium current antagonists, despite the fact that sarcoplasmic reticulum still contains calcium that can be released by caffeine (with inhibition of this release by ryanodine). These three findings are strongly in favor of a calcium-induced release of calcium and against the hypothesis of charge-movement-coupled release of calcium from the sarcoplasmic reticulum. [4] The only finding that would be more in favor of the latter hypothesis (although till reconciliable with the former) is that repolarization occurring before the rapid rise of calcium transient is complete curtails the calcium transient. Thus, the possibility that charge movement might somehow regulate calcium-induced release of calcium cannot be excluded.
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    The effect of acidosis on excitation-contraction coupling in isolated ferret heart muscle (1989)
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 169-173 
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    ISSN: 1573-4919
    Keywords: pH ; calcium ; heart muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The contractile response to acidosis is the final product of a number of different changes in the excitation-contraction coupling pathway: (i) Cai increases and subsequently decreases during acidosis; (ii) the action potential becomes longer; (iii) the sensitivity of the contractile proteins to Ca2+ decreases. The increase of Cai and the lengthening of the action potential may help to maintain contractile function, although this advantage may be offset if spontaneous Ca2− release from the s.r. occurs, secondary to the increase of Cai. The recovery of force shown in figure 1 occurs at a time when the calcium transient is decreasing, and therefore represents an increasing sensitivity of the contractile proteins to Cai, probably due to a recovery of intracellular pH(6), although it is also possible that a disappearance of spontaneous Ca2+ releases from the s.r. may be contributing [2].
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    The interaction between calcium and the activation of Na+, K+-ATPase by noradrenaline (1985)
    Springer
    Molecular and cellular biochemistry 66 (1985), S. 111-116 
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    ISSN: 1573-4919
    Keywords: Adenosine triphosphatase ; Na+ ; K+ ; catecholamines ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary The interaction of noradrenaline, various cation chelators and calcium on Na+, K+-ATPase from rat cerebral cortex plasma membranes was studied. It was shown that chelation of inhibitory cations by EGTA, EDTA and dipyridyl activated Na+, K+-ATPase to the same extent as noradrenaline but at higher concentrations; increasing concentrations of EGTA depressed the activation by noradrenaline; calcium in the form of a calcium-EGTA buffer depressed Na+, K+-ATPase at physiological concentrations; the inhibition of Na+, K+-ATPase by calcium is dependent on the magnesium concentration in the assay and the inhibition by calcium was partially reversed by noradrenaline.
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    Cation-dependent gonadotropin releasing hormone activation of guanylate cyclase (1985)
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    Molecular and cellular biochemistry 66 (1985), S. 145-149 
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    ISSN: 1573-4919
    Keywords: calcium ; cyclic GMP ; gonadotropin releasing hormone ; guanylate cyclase ; manganese
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Gonadotropin releasing hormone enhanced guanylate cyclase [E.C.4.6.1.2] two- to threefold in pituitary, testis, liver and kidney. Dose response relationships revealed that at a concentration of 1 nanomolar, gonadotropin releasing hormone caused a maximal augmentation of guanylate cyclase activity and that increasing its concentration to the millimolar range caused no further enhancement of this enzyme. There was an absolute cation requirement for gonadotropin releasing hormone's enhancement of guanylate cyclase activity as there was no increase without any cation present. Gonadotropin releasing hormone could increase guanylate cyclase activity with either calcium or manganese in the incubation medium but more augmentation was observed with manganese. The data in this investigation suggest that guanylate cyclase may play a role in the mechanism of action of gonadotropin releasing hormone.
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    Regulation of calcium handling by rat parotid acinar cells (1988)
    Springer
    Molecular and cellular biochemistry 82 (1988), S. 67-73 
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    ISSN: 1573-4919
    Keywords: neurotransmitter control ; secretion ; exocrine ; salivary gland ; calcium ; ATP-dependent calcium transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Salivary gland fluid secretion following neurotransmitter stimulation is Ca2+-dependent. We have studied the control of cellular Ca2+ following secretory stimuli in rat parotid gland acinar cells. After muscarinic-cholinergic receptor activation, cytosolic Ca2+ is elevated 4–5 fold, due to both intracellular Ca2+ pool mobilization and extracellular Ca2+ entry. Fluid movement ensues due to the Ca2+-activated enhancement of membrane permeability to K+ and Cl−. Basal cytosolic Ca2+ levels are tightly controlled at ∼150–200 nM through the action of high affinity and high capacity ATP-dependent Ca2+ transporters in the basolateral and endoplasmic reticulum membranes. Activity of these Ca2+ transporters can be modulated to facilitate rapid responsiveness and a sustained fluid secretory response necessary for alimentary function.
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    Ca2+ ionophores inhibit superoxide generation by chemotactic peptide in rabbit neutrophils and the correlation with intracellular calcium (1988)
    Springer
    Molecular and cellular biochemistry 84 (1988), S. 97-103 
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    ISSN: 1573-4919
    Keywords: neutrophils ; A23187 ; lasalocid ; calcium ; superoxide ; chemotactic peptide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Effects of Ca2+ ionophores, A23187 and lasalocid, on superoxide anion generation by chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine methyl ester, in rabbit peritoneal exudate neutrophils were studied. The ionophores by themselves did not activate superoxide anion generation in these neutrophils. When preincubated with the cells for 2 min, both the ionophores inhibited superoxide generation induced by chemotactic peptide. The inhibition was present even in the absence of extracellular Ca2+ and the inhibition was better then. Lasalocid produces a dose-dependent chlortetracycline fluorescence decrease response in neutrophils loaded with chlortetracycline. This response is independent of extracellular Ca2+ concentration and is related to release of Ca2+ from intracellular storage sites. The dose-range at which lasalocid gives this response is same as the dose-range at which it causes inhibition of superoxide response. It may be concluded that the inhibition of superoxide generation by these ionophores is correlated to intracellular Ca2+ modulation.
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    The contribution of mitochondrial calcium ion exchange to relaxation of tension in cardiac muscle (1989)
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    Molecular and cellular biochemistry 89 (1989), S. 127-133 
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    ISSN: 1573-4919
    Keywords: mitochondria ; sarcoplasmic reticulum ; calcium ; myocytes ; caffeine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The possible contribution of mitochondrial Ca2+ accumulation and release to contractile phenomena has been investigated. Two intracellular fractions of Ca2+ sequestration can be identified in cardiac myocytes, one ascribed to mitochondria. Two modes of Ca2+ transport exist within the mitochondrial fraction, one dependent upon mitochondrial respiration and the other upon extramitochondrial [Na+]. Experiments with trabeculae show that under appropriate conditions, the rate of relaxation and the amount of tension developed is dependent on these two modes of Ca2+ transport. A model is presented quantifying the contribution of the mitochondria to relaxation.
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    The control of calcium influx by cytoplasmic calcium in mammalian heart muscle (1989)
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 109-113 
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    ISSN: 1573-4919
    Keywords: heart muscle ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The role of Ca2+ in the initiation and maintenance of contraction has been extensively studies. Many of these studies have focused on how Ca2+ influx and efflux affect cytoplasmic Ca2+ (Cai) and, therefore, contraction in cardiac muscle. However, it has recently become apparent that Cai itself may play a major role in the control of Ca2+ influx and efflux from cardiac muscle. Here we review current ideas on the mechanisms underlying Ca2+ homeostasis in cardiac muscle, with specific attention to how Cai may control Ca2+ influx, both under normal and pathological conditions.
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    Redistribution of subcellular calcium in rat liver on administration of vanadate (1989)
    Springer
    Molecular and cellular biochemistry 90 (1989), S. 155-164 
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    ISSN: 1573-4919
    Keywords: polyvanadate ; mitochondria ; calcium ; pyruvate dehydrogenase ; receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Mitochondria isolated from the livers of rats administered with sodium meta-, ortho-, or polyvanadate, but not vanadyl sulphate, exhibited enhanced Ca2+ — stimulated respiration and uptake of calcium. These effects were shown also by mitochondria isolated from livers perfused with polyvanadate. The concentration of acid-soluble calcium decreased significantly in the mitochondrial fraction on vanadate treatment, while that in the cytosol showed a corresponding increase. Phenoxybenzamine, an antagonist to a-adrenergic receptors, effectively inhibited vanadate-induced Ca2+ mobilization, but surgical sympathectomy was without effect. This is the first demonstration of vanadate mimicking α-adrenergic agonists in vivo.
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    The influence of harmaline on the movements of sodium ions in smooth muscle of the guinea pig ileum (1985)
    Springer
    Molecular and cellular biochemistry 67 (1985), S. 145-150 
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    ISSN: 1573-4919
    Keywords: calcium ; harmaline ; smooth muscle ; sodium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary The effect of changing the extracellular concentration of both Na+ and K+ on the longitudinal muscle of the guinea-pig ileum was studied in the presence and absence of harmaline. A decrease in extracellular Na+ concentration was found to produce a dose-dependent contractile response, which may suggest the existence of a Na...Ca exchange mechanism in this muscle. Harmaline (2 × 10−4 M) was found to reversibly inhibit this contraction and was also found to selectively block the tonic component of high-K induced contradictions. In view of the fact that harmaline is a non-competitive inhibitor of Ca-induced contractions (Hider et al., Europ. J. Pharmacol., 71, 87, 1981), the action of harmaline was interpreted as being a specific inhibitor of the Na... exchange mechanism, binding specifically to Na+ coordination sites.
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    Pancreatic islets contain the M2 isoenzyme of pyruvate kinase its phosphorylation has no effect on enzyme activity (1985)
    Springer
    Molecular and cellular biochemistry 68 (1985), S. 115-120 
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    ISSN: 1573-4919
    Keywords: pyruvate kinase isoenzymes ; pancreatic islets ; kinetic and immunological studies ; calcium ; alanine ; phenylalanine ; fructose bisphosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract To determine which of the major isoenzymes of pyruvate kinase pancreatic islet pyruvate kinase most resembled, it was compared to pyruvate kinase from other tissues in kinetic and immunologic studies. The pattern of activation by fructose bisphosphate and the patterns of inhibition by alanine and phenylalanine were most similar to those of the M2 isoenzyme from kidney and were dissimilar to those of the isoenzymes from skeletal muscle (type M1) and liver (type L). The islet pyruvate kinase was inhibited by anti-M1 pyruvate kinase serum (which crossreacts with the M2 isoenzyme), but not by anti-L pyruvate kinase. These results are most consistent with islets possessing predominantly, if not exclusively, the M2 isoenzyme of pyruvate kinase. We previously showed that rat pancreatic islet cytosol contains protein kinases that can catalyze a calcium-activated phosphorylation of an endogenous peptide that has properties, such as subunit molecular weight and isoelectric pH, that are identical to those of the M2 and M, isoenzymes of pyruvate kinase, and that islet cytosol can catalyze phosphorylation of muscle pyruvate kinase. In the present study it was shown that incubating islet cytosol with ATP under conditions known to permit phosphorylation and inhibition of liver pyruvate kinase did not affect the islet pyruvate kinase activity. It is concluded that phosphorylation of the islet pyruvate kinase has no immediate effect on enzyme activity.
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    Dissociation of the metabolic from the contractile response to muscarinic stimulation in the rabbit urinary bladder (1988)
    Springer
    Molecular and cellular biochemistry 81 (1988), S. 137-143 
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    ISSN: 1573-4919
    Keywords: bladder ; muscarinic stimulation ; metabolism ; bethanecol ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The calcium dependence of contraction and NADH flurorescence was investigated in rabbit bladder stimulated with bethanechol or KCl. The absence of calcium in the bathing solution induced a rightward shift in the dose response to bethanechol for both contraction and NADH flurorescence. The contractile response was shifted to a greater degree than the fluorescence response and the maximal response to bethanechol was reduced by 80% for contraction but only 20% for NADH fluorescence. This rightward shift was also induced by the benzothiazepine calcium antagonist diltiazem (200 μM) and again the contractile response was shifted significantly more than the fluorescence response. The combination of zero calcium and 200 μM diltiazem virtually abolished contractions but only inhibited the NADH fluorescence by 65% at maximally effective bethanechol concentrations. Unlike the effect of diltiazem on the response to bethanechol, diltiazem (200 μM) shifted both the contraction and fluorescence curves to the right equally in response to KCl stimulation. These results indicate that a metabolic response to muscarinic stimulation (decreased NADH) can occur in the absence of any observable contractile response. This metabolic response may be due to post receptor signal processing events. For KCl stimulation, the NADH response is probably secondary to and a result of the contractile response.
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    Regulation of exocytosis in electrically permeabilized insulin-secreting cells. Evidence for Ca2+ dependent and independent secretion (1987)
    Springer
    Bioscience reports 7 (1987), S. 443-454 
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    ISSN: 1573-4935
    Keywords: calcium ; exocytosis ; insulin secretion ; permeabilized cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The regulation of insulin secretion from RINm5F cells exposed to high voltage discharge has been investigated. Electron microscopy revealed that the overall structure of the cells was preserved after permeabilization. In this preparation insulin release was stimulated by Ca2+ (EC50=2.4 μM). The stable GTP analogue GTPγS enhanced secretion both at intermediate (nano- to micromolar) and vanishingly low (〈10 pM) Ca2+ concentrations. At optimal Ca2+ (10 μM) the effect of GTPγS was greatly reduced. We investigated whether the secretory response to GTP analogues was mediated by any of three enzyme systems regulated by GTP-binding proteins, i.e. generation of cyclic AMP by adenylate cyclase, of diacylglycerol by phospholipase C and of arachidonic acid by phospholipase A2. The involvement of these messenger systems could be excluded as (i) cyclic AMP only had minor, Ca2+ dependent effects, (ii) phospholipase C was not activated in the absence of Ca2+ and insulin secretion due to the phorbol ester TPA displayed a different Ca2+ dependency, (iii) arachidonic acid did not elicit Ca2+ independent insulin secretion. These results, taken together with the finding that insulin secretion due to Ca2+ or TPA is attenuated by the inhibitory guanine nucleotide GDPβS, suggest the existence of a regulatory site in exocytosis which is sensitive to guanine nucleotides.
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    A novel role of Ca2+ and Zn2+: Protection of cells against membrane damage (1988)
    Springer
    Bioscience reports 8 (1988), S. 579-583 
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    ISSN: 1573-4935
    Keywords: calcium ; zinc ; membrane protection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Certain cytotoxic agents damage cells by the induction of pores across their plasma membrane. Ca2+ and Zn2+ protect against such damage by promoting pore closure. Zn2+ may play a beneficial role in this regard in certain disease states.
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    URL: http://dx.doi.org/10.1007/BF01117337
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    ATP inhibits onset of exocytosis in permeabilised mast cells (1989)
    Springer
    Bioscience reports 9 (1989), S. 99-109 
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    ISSN: 1573-4935
    Keywords: mast cells ; exocytosis ; G-protein ; GE ; calcium ; ATP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract ATP is not required for exocytosis from permeabilised mast cells, and therefore there is no direct role for protein phosphorylation in the late stages of the activation pathway. We have measured the timecourse of exocytosis from permeabilised cells triggered to release hexosaminidase following addition of Ca2+ to cells equilibrated for 2 min with GTP-γ-S. If ATP is included at the time of permeabilisation, then exocytosis commences after a delay, the duration of which depends on the square root of the product [Ca2+][GTP-γ-S], and which may extend to beyond 3 min. When ATP is excluded then the maximal rate of exocytosis is established within 3 secs of completing the effector combination. These results suggest that the achievement of a new steady-state, induced by Ca2+ and GTP-γ-S, and required for exocytosis is inhibited by ATP. From this we conclude that dephosphorylation of an unknown regulator protein may comprise a step in the exocytotic pathway.
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    Defective regulation of apical membrane chloride transport and exocytosis in cystic fibrosis (1988)
    Springer
    Bioscience reports 8 (1988), S. 27-33 
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    ISSN: 1573-4935
    Keywords: cystic fibrosis ; chloride transport ; exocytosis ; calcium ; calmodulin ; B-adrenergic ; cyclic AMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract A biochemical link is proposed between recent observations on defective regulation of Cl− transport in CF respiratory epithelial cells and studies showing altered biological activity of calmodulin in exocrine glands from CF patients. A consensus is emerging that defective β-adrenergic secretory responsiveness in CF cells is caused by a defect in a regulator protein at a site distal to cyclic AMP formation. Our results indicate that this protein might be a specific calmodulin acceptor protein which modifies the activity of calmodulin in epithelial cells. Alteration in Ca2+/calmodulin dependent regulation of Cl− transport and protein secretion could explain (i) alterations in Ca2+ homeostasis seen in CF, (ii) defective β-adrenergic responses of CF cells, and (iii) the observed inability of cyclic AMP (acting via its specific protein kinase, A-kinase) to open apical membrane Cl− channels in CF epithelial cells. Most of the physiological abnormalities of CF including elevated sweat electrolytes and hyperviscous mucus can be explained on this basis.
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    Exocytosis reconstituted from the sea urchin egg is unaffected by calcium pretreatment of granules and plasma membrane (1988)
    Springer
    Bioscience reports 8 (1988), S. 335-343 
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    ISSN: 1573-4935
    Keywords: calcium ; exocytosis ; sea urchin egg ; phosphoinositide ; diacylglycerol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Micromolar calcium ion concentrations stimulate exocytosis in a reconstituted system made by recombining in the plasma membrane and cortical secretory granules of the sea urchin egg. The isolated cortical granules are unaffected by calcium concentrations up to 1 mM, nor do granule aggregates undergo any mutual fusion at this concentration. Both isolated plasma membrane and cortical granules can be pretreated with 1 mM Ca before reconstitution without affecting the subsequent exocytosis of the reconstituted system in response to micromolar calcium concentrations. On reconstitution, aggregated cortical granules will fuse with one another in response to micromolar calcium provided that one of their number is in contact with the plasma membrane. If exocytosis involves the generation of lipid fusogens, then these results suggest that the calcium-stimulated production of a fusogen can occur only when contiguity exists between cortical granules and plasma membrane. They also suggest that a substance involved in exocytosis can diffuse and cause piggy-back fusion of secretory granules that are in contact with the plasma membrane. Our results are also consistent with a scheme in which calcium ions cause a reversible, allosteric activation of an exocytotic protein.
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    URL: http://dx.doi.org/10.1007/BF01115224
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    Calcium and diacylglycerol control of secretion (1987)
    Springer
    Bioscience reports 7 (1987), S. 355-367 
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    ISSN: 1573-4935
    Keywords: calcium ; diacylglycerol ; exocytosis ; secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Measurements of intracellular Ca2+ in adrenal medullary cells suggest that a transient rise in Ca2+ leads to a transient secretory response, the rise in Ca2+ being brought about by an influx through voltage-sensitive Ca channels which subsequently inactivate. The level of Ca2+ observed is much smaller than the Ca2+ needed to trigger secretion when introduced directly into the cell. The discrepancy is removed by the presence of diacylglycerot, which increases the sensitivity of the secretory process to Ca2+. The site of action of Ca2+ and diacylglycerol is probably protein kinase C, and tile different secretory responses to increases of Ca2+ and diacylglycerol can be modelled in terms of a preferential order of binding of these two substrates to the enzyme. ATP is needed for secretion: one role is possibly to confer stability to the secretory apparatus; another may involve phosphorylation of some key protein. The kinetics of secretion suggest that if Ca2+ regulates phosphorylation or dephosphorylation, then it is therate of change of phosphorylation that controls secretion rather than theextent of phosphorylation or dephosphorylation. Guanine nucleotide-binding proteins may play a role not only at the level of signal transduction coupling, but also at or near the site of exocytosis, and the mechanism by which some Botulinum toxins inhibit secretion may be associated with these proteins.
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    How calcium may cause exocytosis in sea urchin eggs (1987)
    Springer
    Bioscience reports 7 (1987), S. 383-397 
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    ISSN: 1573-4935
    Keywords: calcium ; eggs ; exocytosis ; sea urchin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The process of secretory granule-plasma membrane fusion can be studied in sea urchin eggs. Micromolar calcium concentrations are all that is required to bring about exocytosisin vitro. I discuss recent experiments with sea urchin eggs that concentrate on the biophysical aspects of granule-membrane fusion. The backbone of biological membranes is the lipid bilayer. Sea urchin egg membrane lipids have negatively charged head groups that give rise to an electrical potential at the bilayer-water interface. We have found that this surface potential can affect the calcium required for exocytosis. Effects on the surface potential may also explain why drugs like trifluoperazine and tetracaine inhibit exocytosis: they absorb to the bilayer and reduce the surface potential. The membrane lipids may also be crucial to the formation of the exocytotic pore through which the secretory granule contents are released. We have measured calcium-induced production of the lipid, diacylglycerol. This lipid can induce a phase transition that will promote fusion of apposed lipid bilayers. The process of exocytosis involves the secretory granule core as well as the lipids of the membrane. The osmotic properties of the granule contents lead to swelling of the granule during exocytosis. Swelling promotes the dispersal of the contents as they are extruded through the exocytotic pore. The movements of water and ions during exocytosis may also stabilize the transient fusion intermediate and consolidate the exocytotic pore as fusion occurs.
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    A comparison of bradykinin, angiotensin II and muscarinic stimulation of cultured bovine adrenal chromaffin cells (1989)
    Springer
    Bioscience reports 9 (1989), S. 243-252 
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    ISSN: 1573-4935
    Keywords: secretion ; exocytosis ; chromaffin cell ; calcium ; bradykinin ; angiotensin II, muscarinic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Bradykinin, angiotensin II and a mascarnic agonist, acetyl-B-methacholine (methacholine) were all found to elict catecholamine release from cultured bovine adrenal chromaffin cells. Bradykinin was the most potent of these secretagogues and methacholine the weakest, with angiotenin II intermediate in efficacy. All three secretagogues were much less effective than nicotinic stimulation. The three secretagogues all produced a rise in cytoplasmic free calcium concentration ([Ca2+]i), measured with the fluorescent indicator fura2, which was partially independent of external calcium. In the case of bradykinin the full rise in ([Ca2+]i) may involve a component of calcium entry in addition to release of calcium from an internal store. Secretion was also found to be partially independent of external calcium. The different efficacies of the three secretagogues in elicting secretion were correlated with the rise in ([Ca2+]i) produced. The differeing efficacies of the three secretagogues may be due to the extent of release of calcium from an intracellular store which itself is less effective in eliciting secretion than a rise in [Ca2+]i following calcium entry due to nicotine. Bradykinin also stimulates calcium entry, and this may increase the efficacy of the initial rise in [Ca2+]i. Treatment with pertussis toxin resulted in an enhancement of secretion in response to all of the secretagogues.
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    The molecular and biochemical basis of cystic fibrosis (1987)
    Springer
    Bioscience reports 7 (1987), S. 167-185 
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    ISSN: 1573-4935
    Keywords: cystic fibrosis ; exocrine ; autonomic ; cyclic AMP ; calcium ; chloride ; epithelial
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1007/BF01124787
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    A nonselective cation channel activated by membrane deformation in oocytes of the ascidianBoltenia villosa (1989)
    Springer
    The journal of membrane biology 107 (1989), S. 179-188 
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    ISSN: 1432-1424
    Keywords: stretch-activated channel ; calcium ; oocyte ; development ; patch clamp ; tunicate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Cell-attached patch clamp recordings from unfertilized oocytes of the ascidianBoltenia villosa reveal an ion channel which is activated by mechanical deformation of the membrane. These channels are seen when suction is applied to the patch pipette, but not in the absence of suction or during voltage steps. The estimated density of these stretch-activated channels is about 1.5/μm2, a figure equal to or greater than the density of known voltage-dependent channels in the oocyte. Ion substitution experiments done with combined whole-cell and attached patch recording, so absolute potentials are known, indicate that the channel passes Na+, Ca2+ and K+, but not Cl−. The channel has at least two open and two closed states, with the rate constant that leaves the longer-lived closed state being the primary site of stretch sensitivity. External Ca2+ concentration affects channel kinetics: at low calcium levels, long openings predominate, whereas at high calcium virtually all openings are to the short-lived open state. In multiple channel patches, the response to a step change in suction is highly phasic, with channel open probability decreasing over several hundred milliseconds to a nonzero steady-state level after an initial rapid increase. This channel may play a role in the physiological response of cells of the early embryo to the membrane strains associated with morphogenetic events.
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    Ca2+-activated K+ channels in the apical membrane ofNecturus choroid plexus (1988)
    Springer
    The journal of membrane biology 105 (1988), S. 207-219 
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    ISSN: 1432-1424
    Keywords: choroid plexus ; brush border membrane ; Ca2+-activated K+ channels ; calcium ; barium ; TEA ; intracellular pH ; cerebrospinal fluid secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The properties of Ca2+-activated K+ channels in the apical membrane of theNecturus choroid plexus were studied using single-channel recording techniques in the cell-attached and excised-patch configurations. Channels with large unitary conductances clustered around 150 and 220 pS were most commonly observed. These channels exhibited a high selectivity for K+ over Na+ and K+ over Cs+. They were blocked by high cytoplasmic Na+ concentrations (110mm). Channel activity increased with depolarizing membrane potentials, and with increasing cytoplasmic Ca2+ concentrations. Increasing Ca2+ from 5 to 500nm, increased open probability by an order of magnitude, without changing single-channel conductance. Open probability increased up to 10-fold with a 20-mV depolarization when Ca2+ was 500nm. Lowering intracellular pH one unit, decreased open probability by more than two orders of magnitude, but pH did not affect single-channel conductance. Cytoplasmic Ba2+ reduced both channel-open probability and conductance. The sites for the action of Ba2+ are located at a distance more than halfway through the applied electric field from the inside of the membrane. Values of 0.013 and 117mm were calculated as the apparent Ba2+ dissociation constants (K d (0 mV) for the effects on probability and conductance, respectively. TEA+ (tetraethylammonium) reduced single-channel current. Applied to the cytoplasmic side, it acted on a site 20% of the distance through the membrane, with aK d (0 mV)=5.6mm. A second site, with a higher affinity,K d (0 mV)=0.23mm, may account for the near total block of chanel conductance by 2mm TEA+ applied to the outside of the membrane. It is concluded that the channels inNecturus choroid plexus exhibit many of the properties of “maxi” Ca2+-activated K+ channels found in other tissues.
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    Ca2+-activated K+ currents inNecturus choroid plexus (1988)
    Springer
    The journal of membrane biology 105 (1988), S. 221-231 
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    ISSN: 1432-1424
    Keywords: choroid plexus ; calcium-activated potassium currents ; cerebrospinal fluid secretion ; calcium ; delayed currents ; patch clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The tight-seal whole-cell recording method has been used to studyNecturus choroid plexus epithelium. A cell potential of −59±2 mV and a whole cell resistance of 56±6 MΩ were measured using this technique. Application of depolarizing step potentials activated voltage-dependent outward currents that developed with time. For example, when the cell was bathed in 110mm NaCl Ringer solution and the interior of the cell contained a solution of 110mm KCl and 5nm Ca2+, stepping the membrane potential from a holding value of −50 to −10 mV evoked outward currents which, after a delay of greater than 50 msec, increased to a steady state in 500 msec. The voltage dependence of the delayed currents suggests that they may be currents through Ca2+-activated K_ channels. Based on the voltage dependence of the activation of Ca2+-activated K+ channels, we have devised a general method to isolate the delayed currents. The delayed currents were highly selective for K+ as their reversal potential at different K+ concentration gradients followed the Nernst potential for K+. These currents were reduced by the addition of TEA+ to the bath solution and were eliminated when Cs+ or Na+ replaced intracellular K+. Increasing the membrane potential to more positive values decreased both the delay and the half-times (t 1/2) to the steady value. Increasing the pipette Ca2+ also decreased the delay and decreasedt 1/2. For instance, when pipette Ca2+ was increased from 5 to 500nm, the delay andt 1/2 decreased from values greater than 50 and 150 msec to values less than 10 and 50 msec. We conclude that the delayed currents are K+ currents through Ca2+-activated K+ channels. At the resting membrane potential of −60 mV, Ca2+-activated K+ channels contribute between 13 to 25% of the total conductance of the cell. The contribution of these channels to cell conductance nearly doubles with membrane depolarization of 20–30 mV. Such depolarizations have been observed when cerebrospinal fluid (CSF) secretion is stimulated by cAMP and with intracellular Ca2+. Thus the Ca2+-activated K+ channels may play a specific role in maintaining intracellular K+ concentrations during CSF secretion.
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    Tight junction formation in cultured epithelial cells (MDCK) (1985)
    Springer
    The journal of membrane biology 86 (1985), S. 113-125 
    Details
    ISSN: 1432-1424
    Keywords: epithelial monolayers ; MDCK cells ; tight junctions ; calcium ; biosynthesis of junctions ; junctional assembly ; apical/basolateral polarization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Synthesis and assembly of tight junctions are studied in monolayers of MDCK cells plated at a density sufficient for confluence, allowed to attach for 1 hr, and transferred to fresh media without cells containing or not Ca2+, 20 hr later, while monolayers with Ca2+ have fully developed junctions that confer an electrical resistance across of 346±51 Ω cm2, those without Ca2+ have a negligible resistance. If at this time Ca2+ is added, junctions assemble and seal with a fast kinetics, that can be followed through the development of electrical resistance, penetration of ruthenium red, and electron microscopy. Drugs that impair synthesis, maturation and transport of proteins (cycloheximide, tunicamycin, monensin) indicate that protein components are synthesized early upon plating, do not seem to require N-glycosylation, and are stored in the Golgi compartment. Upon addition of Ca2+ they are transferred to the membrane with the participation of microfilaments but not of microtubules. These components seem to insert directly in the position they occupy in the strands, and the cell circles its perimeter with one strand as early as 15 min, even if in some segments it only consists of a row of particles. New strands develop in association with previous ones, and the pattern completes in 4 to 6 hr. Ca2+ is required for the maintenance of the assembly and also for the sealing with neighboring cells. These processes cannot occur below 25°C. Serum is not required. Polarized distribution of intramembrane particles (IMP) in apical and basolateral regions follows the same time course as junction formation, in spite of the fence constituted by those strands that are already assembled. This suggests that IMP do not redistribute by lateral displacements in the plane of the membrane, but by removal and insertion in the apical and basolateral domains.
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    Electric pulse-induced fusion of mouse lymphoma cells: Roles of divalent cations and membrane lipid domains (1985)
    Springer
    The journal of membrane biology 85 (1985), S. 269-280 
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    ISSN: 1432-1424
    Keywords: cell fusion ; electrofusion ; dielectrophoresis ; calcium ; magnesium ; membrane lipid ; lymphoma cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Mouse leukemic lymphoblasts (L5178Y) brought into close contact by dielectrophoresis underwent cell fusion following the application of electrical pulses in the presence of electrolytes. The electrically fused cells became spherical after switching off the dielectrophoretic field. Fusion between a cell vitally stained with Janus Green and that with Neutral Red resulted in the homokaryon with a mixed color. Intracellular potentials simultaneously recorded from the two cells located on both sides of the homokaryon were identical. The fusion efficiency was remarkably dependent upon temperature, displaying a discontinuity at about 11°C in the Arrhenius plot. The extracellular application of phospholipase-A2 or-C suppressed the fusion yield. Thus, it appears that the phospholipid domains play a crucial role in the electric pulse-induced cell fusion. Treatment of the cells with proteolytic enzymes markedly enhanced the fusion yield, presumably due to removing the glycocalix and/or giving rise to fusion-potent, protein-free lipid domains. The presence of millimolar concentrations of divalent cations (irrespective of Mg2+ or Ca2+) as well as of micromolar concentrations of Ca2+ (but not Mg2+) was prerequisite to the resealing of membranes suffered from electrical breakdown upon exposure to electric pulses. In addition, extracellular Ca2+ (but not Mg2+) ions at more than micromolar concentrations were indispensable for the cell fusion.
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    Single Cl− channels in molluscan neurones: Multiplicity of the conductance states (1985)
    Springer
    The journal of membrane biology 86 (1985), S. 9-15 
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    ISSN: 1432-1424
    Keywords: molluscan neurone ; patch voltage-clamp technique ; single Cl channel ; calcium ; potassium ; multiplicity of the condutance states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Properties of the single Cl− channels were studied in excised patches of surface membrane from molluscan neurones using single-channel recording technique. These channels are controlled by Ca2+ and K+ acting on cytoplasmic and outer membrane surfaces, respectively, and by the membrane potential. The channels display about 16 intermediate conductance sublevels, each of them being multiples of ∼12.5 pS. The upper level of the channel conductance is about 200 pS. The channel behavior is consistent with an aggregation of channel-forming subunits into a cluster.
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    The role of phosphoinositiees in signal transduction (1986)
    Springer
    The journal of membrane biology 89 (1986), S. 193-210 
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    ISSN: 1432-1424
    Keywords: phosphoinositides ; phosphatidylinositol ; inositol-1,4,5-trisphosphate ; diacylglycerol ; arachidonic acid ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1007/BF01870664
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    The chromaffin granule proton pump and calcium-dependent exocytosis in bovine adrenal medullary cells (1985)
    Springer
    The journal of membrane biology 83 (1985), S. 147-156 
    Details
    ISSN: 1432-1424
    Keywords: Exocytosis ; proton pump ; calcium ; secretion ; adrenal medulla
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Calcium-dependent exocytosis in ‘leaky’ bovine adrenal medullary cells has a requirement for Mg-ATP. One possibility is that exocytosis depends in some way on the operation of the ATP-dependent proton pump that serves to maintain the core of the secretory vesicles both acid and at a positive potential with respect to the cytosol. This possibility has been tested in ‘leaky’ cells by monitoring exocytosis under conditions where the secretory vesicle pH and potential gradients are measuredin situ. The results show rather clearly that exocytosis can persist, with unchanged Ca-activation kinetics, in the virtual absence both of a difference in pH between the cytosol and secretory vesicle core and also of a difference in potential across the vesicle membrane. The results do not, however, exclude a small modulating effect of vesicle pH or potential on exocytosis and shed no light on whether or not the plasma membrane potential, which is maintained close to zero in these experiments, influences exocytosis.
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    Effects of membrane potential on sodium-dependent calcium uptake by sarcolemma-enriched preparations from canine ventricle (1985)
    Springer
    The journal of membrane biology 84 (1985), S. 207-219 
    Details
    ISSN: 1432-1424
    Keywords: sodium/calcium exchange ; excitation-contraction coupling ; sarcolemma ; membrane potential ; sodium ; calcium ; heart
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effect of membrane potential on sodium-dependent calcium uptake by vesicles in an isolated cardiac sarcolemma preparation was examined. Initial time course studies showed that the reaction deviated from initial velocity conditions within minutes. This appeared to be due, in part, to loss of the sodium gradient. Assays carried out to 10 sec revealed a linear component of uptake (2 to 10 sec) and a faster component (complete by 2 sec). The latter was eliminated by loading the preparation with ethyleneglycol-bis-(β-aminoethyl ether)N,N′-tetraacetic acid (EGTA). This maneuver did not affect the slow component, and subsequent studies used preparations containing EGTA. Potassium Nernst potentials (E K), established by potassium gradients in the presence of valinomycin, were varied from −100 to +30 mV by changing [K+] o from 1.18 to 153.7mM ([K+] i =50mM). The initial velocity of sodium-dependent calcium uptake was stimulated twofold by changingE K from −100 to 0 mV and another twofold by raisingE K from 0 to +30 mV. For the total range ofE K and [K+] o , 32 to 36% of the increase appeared to reflect stimulation by extravesicular potassium. The remainder appeared to be due to membrane potential. The profile of sodium-dependent calcium uptake versusE K suggested that calcium influx through electrogenic sodium/calcium exchange may be much more affected by the positive region of the cardiac action potential than by the negative region.
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    Ca2+ buffer sites in intact bovine rod outer segments: Introduction to a novel optical probe to measure ionic permeabilities in suspensions of small particles (1985)
    Springer
    The journal of membrane biology 88 (1985), S. 249-262 
    Details
    ISSN: 1432-1424
    Keywords: calcium ; rod photoreceptors ; surface potentials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The nature of the Ca2+ buffer sites in intact rod outer segments isolated from bovine retinas (ROS) was investigated. The predominant Ca2+ buffer in intact ROS was found to be negatively charged groups confined to the surface of the disk membranes. Accordingly, Ca2+ buffering in ROS was strongly influenced by the electrostatic surface potential. The concentration of Ca2+ buffer sites was about 30mm, 80% of which were located at the membrane surface in the intradiskal space. A comparison with observations in model systems suggests that phosphatidylserine is the major Ca2+ buffer site in ROS. Protons and alkali cations could replace Ca2+ as mobile counterions for the fixed negatively charged groups. At physiological ionic strength, the total number of these diffusible, but osmotically inactive, counterions was as large as the number of osmotically active cations in ROS. The surface potential is dependent on the concentration of cations in ROS and can be measured with the optical dye neutral red. Addition of cations to the external solution led to the release of the internally bound dye as the cations crossed the outer membrane. The chemical and spectral properties of the dye enable its use as a real-time indicator of cation transport across the outer envelope of small particles in suspension. In this study, the dye method is illustrated by the use of well-defined ionophores in intact ROS and in liposomes. In the companion paper this method is used to describe the cation permeabilities native to ROS.
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    Electrophysiological evidence suggests a defective Ca2+ control mechanism in a newParamecium mutant (1987)
    Springer
    The journal of membrane biology 98 (1987), S. 275-283 
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    ISSN: 1432-1424
    Keywords: Paramecium ; calcium ; cilia ; mutants ; Ca2+ pump ; Ca2+ buffering ; ion channels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A new mutant ofParamecium tetraurelia, k-shyA, was characterized behaviorally and electrophysiologically. The mutant cell exhibited prolonged backward swimming episodes in response to depolarizing conditions. Electrophysiological comparison of k-shyA with wild type cells under voltage clamp revealed that the properties of three Ca2+-regulated currents were altered in the mutant. (i) The voltage-dependent Ca2+ current recovered from Ca2+-dependent inactivation two- to 10-fold more slowly than wild type. Ca2+ current amplitudes were also reduced in the mutant, but could be restored by EGTA injection. (ii) The decay of the Ca2+-dependent K+ tail current was slower in the mutant. (iii) The decay of the Ca2+-dependent Na+ tail current was also slower in the mutant. All other membrane properties studied, including the resting membrane potential and resistance and the voltage-sensitive K+ currents, were normal in k-shyA. Considered together, these observations are consistent with a defect in the ability of k-shyA to reduce the free intracellular Ca2+ concentration following stimulation. The possible targets of the genetic lesion and alternative explanations are discussed. The k-shy mutants may provide a useful tool for molecular and physiological analyses of the regulation of Ca2+ metabolism inParamecium.
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    Na+/K+/Cl− cotransport in cultured vascular smooth muscle cells: Stimulation by angiotensin II and calcium ionophores, inhibition by cyclic AMP and calmodulin antagonists (1987)
    Springer
    The journal of membrane biology 99 (1987), S. 51-63 
    Details
    ISSN: 1432-1424
    Keywords: endothelial cells ; Na+/K+/Cl− cotransport ; cyclic AMP ; phenothiazines ; calcium ; angiotensin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The specific activity of the Na+/K+/Cl− cotransporter was assayed by measuring the initial rates of furosemide-inhibitable86Rb+ influx and efflux. The presence of all three ions in the external medium was essential for cotransport activity. In cultured smooth muscle cells furosemide and bumetanide inhibited influx by 50% at 5 and 0.2 μm, respectively. The dependence of furosemide-inhibitable86Rb+ influx on external Na+ and K+ was hyperbolic with apparentK m values of 46 and 4mm, respectively. The dependence on Cl− was sigmoidal. Assuming a stoichiometry of 1∶1∶2 for Na+/K+/Cl−, aK m of 78mm was obtained for Cl−. In quiescent smooth muscle cells cotransport activity was approximately equal to Na+ pump activity with each pathway accounting for 30% of total86Rb+ influx. Growing muscle cells had approximately 3 times higher cotransport activity than quiescent ones. Na+ pump activity was not significantly different in the gorwing and quiescent cultures. Angiotensin II (ANG) stimulated cotransport activity as did two calcium-transporting ionophores, A23187 and ionomycin. The removal of external Ca2+ prevented A23187, but not ANG, from stimulating the cotransporter. Calmodulin antagonists selectively inhibited86Rb+ influx via the cotransporter. Beta-adrenoreceptor stimulation with isoproterenol, like other treatments which increase cAMP, inhibited cotransport activity. Cultured porcine endothelial cells had 3 times higher cotransport activity than growing muscle cells. Calmodulin antagonists inhibited cotransport activity, but agents which increase cAMP or calcium had no effect on cotransport activity in the endothelial cells.
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    Role of calcium and calmodulin in the regulation of the rabbit ileal brush-border membrane Na+/H+ antiporter (1989)
    Springer
    The journal of membrane biology 108 (1989), S. 207-215 
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    ISSN: 1432-1424
    Keywords: calcium ; calmodulin ; absorption ; ileum ; brush-border vesicle ; phosphorylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In rabbit ileum, Ca2+/calmodulin (CaM) appears to be involved in physiologically inhibiting the linked NaCl absorptive process, since inhibitors of Ca2+/CaM stimulate linked Na+ and Cl− absorption. The role of Ca2+/CaM-dependent phosphorylation in regulation of the brush-border Na+/H+ antiporter, which is believed to be part of the neutral linked NaCl absorptive process, was studied using purified brush-border membrane vesicles, which contain both the Na+/H+ antiporter and Ca2+/CaM-dependent protein kinase(s) and its phosphoprotein substrates. Rabbit ileal villus cell brush-border membrane vesicles were prepared by Mg precipitation and depleted of ATP. Using a freezethaw technique, the ATP-depleted vesicles were loaded with Ca2+, CaM, ATP and an ATP-regenerating system consisting of creatine kinase and creatine phosphate. The combination of Ca2+/CaM and ATP inhibited Na+/H+ exchange by 45±13%. This effect was specific since Ca2+/CaM and ATP did not alter diffusive Na+ uptake, Na+-dependent glucose entry, or Na+ or glucose equilibrium volumes. The inhibition of the Na+/H+ exchanger by Ca2+/CaM/ATP was due to an effect on theV max and not on theK m for Na+. In the presence of CaM and ATP, Ca2+ caused a concentration-dependent inhibition of Na+ uptake, with an effect 50% of maximum occurring at 120nm. This Ca2+ concentration dependence was similar to the Ca2+ concentration dependence of Ca2+/CaM-dependent phosphorylation of specific proteins in the vesicles. The Ca2+/CaM/ATP-inhibition of Na+/H+ exchange was reversed by W13, a Ca2+/CaM antagonist, but not by a hydrophobic control, W12, or by H-7, a protein kinase C antagonist. we conclude that Ca2+, acting through CaM, regulates ileal brush-border Na+/H+ exchange, and that this may be involved in the regulation of neutral linked NaCl absorption.
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    Ca2+-activated K+ channels from cultured renal medullary thick ascending limb cells: Effects of pH (1989)
    Springer
    The journal of membrane biology 110 (1989), S. 49-55 
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    ISSN: 1432-1424
    Keywords: loop of Henle ; potassium secretion ; channels ; acid/base balance ; thick ascending limb ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Ca2+-activated K+ channels were studied in cultured medullary thick ascending limb cells (MTAL) using the patch-clamp technique. The purpose was to determine the effect of acidic pH on channel properties in excised patches of apical cell membrane. At pH 7.4, increasing Ca2+ on the intracellular side or applying positive voltages increases channel open probability. Reducing pH to 5.8 on the intracellular face of the channel decreases channel open probability at each voltage and Ca2+ concentration. Channel mean open times display two distributions and mean closed times display three distributions. Increasing Ca2+ or applying depolarizing voltages lengthens each of the mean open times and shortens each of the closed times. Lowering pH to 5.8 decreases the mean open times and increases mean closed times at each Ca2+ and voltage with the greatest effect on the mean closed times. In contrast, both single-channel conductance and channel kinetics are unaffected when pH is reduced to 5.8 on the extracellular face of the membrane. We conclude that protons interfere with Ca2+ binding to the gate of Ca2+-activated K+ channels reducing the probability of channel opening.
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    Ionic and permeability requirements for exocytosis in vitro in sea urchin eggs (1988)
    Springer
    The journal of membrane biology 101 (1988), S. 199-207 
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    ISSN: 1432-1424
    Keywords: exocytosis ; membrane fusion ; secretion ; calcium ; sea urchin egg ; cortical granule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We study exocytosis in the planar isolated cortex of the egg of the sea urchinLytechinus pictus. Solutins bathing the exocytotic apparatus need not contain appreciable amounts of ions: fusion follows addition of submicromolar calcium to solutions containing only nonelectrolyte. We examine the effects of altering the granule membrane permeability to small molecules with ionophores and digitonin. Introducing holes in the secretory granule membrane to the extent of allowing free passage of small molecules does not cause seretion in vitro. We add the amphipathic compound digitonin at 12 to 15 μM concentrations and demonstrate that the granule membrane can become permeable to lucifer yellow, yet that granules remain intact. Granules still undergo exocytosis after digitonin treatment at such concentrations upon subsequent addition of calcium. Higher concentrations of digitonin lead to granule content swelling and vesicle bursting. We conclude that cortical granule hydration during exocytosis is not mediated by small ionic channels.
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    Effect of phospholipid surface charge on the conductance and gating of a Ca2+-activated K+ channel in planar lipid bilayers (1985)
    Springer
    The journal of membrane biology 83 (1985), S. 273-282 
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    ISSN: 1432-1424
    Keywords: surface charge ; potassium channel ; calcium ; phosphatidylserine ; planar bilayer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A Ca-activated, K-selective channel from plasma membrane of rat skeletal muscle was studied in artificial lipid bilayers formed from either phosphatidylethanolamine (PE) or phosphatidylserine (PS). In PE, the single-channel conductance exhibited a complex dependence on symmetrical K+ concentration that could not be described by simple Michaelis-Menten saturation. At low K+ concentrations the channel conductance was higher in PS membranes, but approached the same conductance observed in PE above 0.4m KCl. At the same Ca2+ concentration and voltage, the probability of channel opening was significantly greater in PS than PE. The differences in the conduction and gating, observed in the two lipids, can be explained by the negative surface charge of PS compared to the neutral PE membrane. Model calculations of the expected concentrations of K+ and Ca2+ at various distances from a PS membrane surface, using Gouy-Chapman-Stern theory, suggest that the K+-conduction and Ca2+-activation sites sense a similar fraction of the surface potential, equivalent to the local electrostatic potential at a distance of 9 Å from the surface.
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    Polycation inhibition of exocytosis from sea urchin egg cortex (1986)
    Springer
    The journal of membrane biology 91 (1986), S. 85-96 
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    ISSN: 1432-1424
    Keywords: exocytosis ; polycations ; cortical lawn ; calcium ; sea urchin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The Ca2+-stimulated release of vesicle contents from cortical fragments prepared from sea urchin eggs is an in vitro model for exocytosis. Cortical fragments have been isolated either in suspension (cell surface complex, CSC preparation), or attached to polycation-coated surfaces (cortical lawn, CL preparation). CL, but not CSC, have been reported to undergo a rapid “aging” process whereby they fail to respond to micromolar free Ca2+. Since, in principle, the only difference between the two preparations is the use of polycations in the CL preparation, polycations were suspected of being inhibitory. This hypothesis was tested by evaluating the effects of polycation-containing buffers on the Ca2+ threshold, rate, and extent of exocytosis in CL prepared from the eggs ofStrongylocentrotus purpuratus. A sensitive microphotometric assay, based on light scattering by the individual cortical vesicles in the CL, was used to quantitate the exocytotic response. Buffers containing polylysine were found to be potent inhibitors of cortical exocytosis. The Ca2+ threshold of CL that had been treated for 15 min at room temperature with 50 μg/ml of polylysine was more than three orders of magnitude greater than that of freshly prepared CL. The other polycations tested (protamine, spermine and neomycin) were also found to be inhibitory, but to a lesser degree than polylysine. Two lines of evidence suggested that the polycations used in the preparation of CL are responsible for the rapid “aging” phenomenon: (i) CSC fragments that had been affixed to polylysine-coated coverslips were shown to aquire “aging” characteristics similar to the CL preparations; control CSC that had been maintained in suspension did not. (ii) Radiolabeled poly-l-lysine was shown to dissociate from coated coverslips and redistribute onto CL.
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    Ca2+ and cAMP activate K+ channels in the basolateral membrane of crypt cells isolated from rabbit distal colon (1989)
    Springer
    The journal of membrane biology 110 (1989), S. 19-28 
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    ISSN: 1432-1424
    Keywords: colon ; ion transport ; ion channel ; cyclic nucleotides ; calcium ; potassium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Using patch-clamp techniques, we have studied Ca2+-activated K+ channels in the basolateral membrane of freshly isolated epithelial cells from rabbit distal colon. Epithelial cell clusters were obtained from distal colon by gentle mechanical disruption of isolated crypts. Gigaohm seals were obtained on the basolateral surface of the cell clusters. At the resting potential (approximately −45 mV), with NaCl Ringer's bathing the cell, the predominant channels had a conductance of 131±25 pS. Channel activity depended on voltage as depolarization of the membrane increased the open probability. In excised inside-out patches, channels were found to be selective for K+ over Na+. Channel activity correlated directly with bath Ca2+ concentration in the excised patches. Channel currents were blocked by 5mm TEA+ and 1mm Ba2+. In cell-attached patches, after addition of the Ca2+ ionophore A23187, which increases intracellular Ca2+, open probability was markedly increased. Channel activity was also regulated by cAMP as addition of 1mm dibutyryl-cAMP in the bath solution in cell-attached patches increased channel open probability over 20-fold. Channels that had been activated by cAMP were further activated by Ca2+. We conclude that the basolateral membrane of epithelial cells from descending colon contains a class of potassium channels, which are regulated by intracellular Ca2+ and cAMP.
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    Transcellular ion currents and extension ofNeurospora crassa hyphae (1988)
    Springer
    The journal of membrane biology 101 (1988), S. 33-41 
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    ISSN: 1432-1424
    Keywords: electric current ; protons ; Neurospora crassa ; pH gradient ; H+-ATPase ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Hyphae ofNeurospora crassa, like many other tipgrowing organisms, drive endogenous electric currents through themselves such that positive charges flow into the apical region and exit from the trunk. In order to identify the ions that carry the current, the complete growth medium was replaced by media lacking various constituents. Omission of K+ or of phosphate diminished the zone of inward current, effectively shifting the current pattern towards the apex. Omission of glucose markedly reduced both inward and outward currents; addition of sodium azide virtually abolished the flow of electric current. Growing hyphae also generate a longitudinal pH gradient: the medium surrounding the apex is slightly more alkaline than the bulk phase, while medium adjacent to the trunk turns acid. The results suggest thatNeurospora hyphae generate a proton current; protons are expelled distally by the H+-ATPase and return into the apical region by a number of pathways, including the symport of protons with phosphate and potassium ions. Calcium influx may also contribute to the electric current that enters the apical region. There seems to be no simple obligatory linkage between the intensity of the transcellular electric current and the rate of hyphal extension. Calcium ions, however, are required in micromolar concentrations for extensions and morphogenesis of hyphal tips.
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    Evidence implicating protein kinase C in exocytosis from electropermeabilized bovine chromaffin cells (1988)
    Springer
    The journal of membrane biology 104 (1988), S. 21-34 
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    ISSN: 1432-1424
    Keywords: exocytosis ; secretion ; calcium ; protein kinase C ; adrenal medulla ; catecholamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The calcium sensitivity of exocytosis from electroper-meabilized chromaffin cells is increased by activators of protein kinase C, such as TPA and certain phorbol esters, diacylglycerols, and mezerein. A range of putative inhibitors of protein kinase C block both the phorbol ester-sensitive component of secretion and also the underlying insensitive component. These inhibitors are also shown to inhibit medulla protein kinase C activity in vitro. The extent of secretion is reduced when electropermeabilized cells are exposed to Ca2+ levels much in excess of 50 μm. The onset of inhibition is faster than the relatively slow rate of Ca-dependent exocytosis and is insensitive to inhibitors of proteolysis. Adrenal medulla protein kinase C activity is also irreversibly inhibited by high Ca2+ concentrations. Both the secretory response and the protein kinase C activity in vitro have similar nucleotide and cation specificities. Although these data do not definitely establish an involvement of protein kinase C in exocytosis, none argue against it.
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    Parathyroid hormone-induced changes of the brush border topography and cytoskeleton in cultured renal proximal tubular cells (1986)
    Springer
    The journal of membrane biology 92 (1986), S. 151-162 
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    ISSN: 1432-1424
    Keywords: kidney ; parathyroid hormone ; angiotensin II ; calcium ; brush border ; cytoskeleton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In order to examine the possibility of parathyroid hormone-mediated ultrastructural rearrangements in target epithelium, isolated canine renal proximal tubular cells were grown on a collagen-coated semipermeable membrane in a defined medium. Scanning and transmission electron microscopy of these monolayers revealed abundant microvilli. Exposure of the proximal tubular cells to parathyroid hormone resulted in a biphasic changes involving: (1) dramatic shortening and rarefaction of microvilli within 1 min; and (2) recovery of microvillar topography after 5 min. A similar shortening of microvilli was observed following exposure to ionomycin, whereas incubation with cyclic AMP resulted in an elongation of microvilli. Parathyroid hormone stimulated cyclic AMP production and increased cytoplasmic free calcium concentration in cultured proximal tubular cells. Pretreatment of cells with a calmodulin inhibitor abolished the effect of parathyroid hormone on brush border topography. Shortening of microvilli was associated with a disappearance of microvillar core filaments. Staining of F-actin with fluoresceinphalloidin showed that parathyroid hormone resulted in fragmentation of stress fibers. It is concluded that parathyroid hormoneinduced cell activation involves cytoplasmic-free calcium, calmodulin, and the cytoskeleton.
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    Role of Ca++ in vasodilator reactions (1986)
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    Bulletin of experimental biology and medicine 101 (1986), S. 150-154 
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    ISSN: 1573-8221
    Keywords: α-adrenoreceptors ; metabolism ; calcium ; hormone-dependent vasodilatation
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    Topics: Biology , Medicine
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    Mechanisms of platelet aggegation in experimental hypoparathyroidism (1986)
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    Bulletin of experimental biology and medicine 102 (1986), S. 1648-1650 
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    ISSN: 1573-8221
    Keywords: hypoparathyroidism ; platelet aggregation ; calcium ; arachidonic acid ; PAF
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    Effect of a calcium channel blocker on pituitary luteinizing hormone secretion in intact and castrated male and female rats (1987)
    Springer
    Bulletin of experimental biology and medicine 103 (1987), S. 400-402 
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    ISSN: 1573-8221
    Keywords: luteinizing hormone ; sex steroids ; calcium ; verapamil
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    Genetic analysis of inheritance of rates of Na+, K+-cotransport, calcium concentration in erythrocytes, and blood pressure of F2 hybrids of spontaneously hypertensive and normotensive rats (1987)
    Springer
    Bulletin of experimental biology and medicine 103 (1987), S. 518-520 
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    ISSN: 1573-8221
    Keywords: calcium ; spontaneous hypertension ; orthovanadate
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    Antioxidant-induced calcium transport in biological membranes (1987)
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    Bulletin of experimental biology and medicine 104 (1987), S. 1220-1223 
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    ISSN: 1573-8221
    Keywords: biological membranes ; antioxidant ; calcium
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    Lowering the stimulated free intracellular calcium level in platelets in the refractory state (1988)
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    Bulletin of experimental biology and medicine 106 (1988), S. 1699-1702 
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    ISSN: 1573-8221
    Keywords: platelets ; aggregation ; refractoriness ; calcium ; ADP
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    Regulation of tetanus toxin-inhibited transmitter release in neuromuscular junctions in a calcium-free medium (1985)
    Springer
    Bulletin of experimental biology and medicine 99 (1985), S. 417-420 
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    ISSN: 1573-8221
    Keywords: rat neuromuscular junction ; calcium ; tetanus toxin ; ouabain
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    c-src Locus determines increased rate of Na+, K+-cotransport and increased calcium content in (SHR×WKY)F2 hybrid erythrocytes (1989)
    Springer
    Bulletin of experimental biology and medicine 108 (1989), S. 1634-1636 
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    ISSN: 1573-8221
    Keywords: c-src locus ; calcium ; Na+, K+-cotransport
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    Homeostatic role of anticalcitonin antibodies in calcium metabolism in experimental diabetes mellitus (1988)
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    Bulletin of experimental biology and medicine 105 (1988), S. 181-183 
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    ISSN: 1573-8221
    Keywords: diabetes mellitus ; calcium ; anticalcitonin antibodies ; reaction of enzyme-labeled antibodies
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    Correlation between calcium biorhythms and helio-geophysical factors (1988)
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    Bulletin of experimental biology and medicine 105 (1988), S. 244-247 
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    ISSN: 1573-8221
    Keywords: biorhythms ; calcium ; immunization ; helio-geophysical rhythms
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    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00835707
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    Dissociation of insulin binding from insulin stimulation of 2-deoxyglucose transport by ruthenium red (1986)
    Springer
    Bioscience reports 6 (1986), S. 317-322 
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    ISSN: 1573-4935
    Keywords: Insulin binding ; insulin action ; glucose transport ; calcium ; ruthenium red
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Ruthenium red increased specific insulin binding to isolated adipocytes 5.4 fold and 2.6 fold over binding determined in the absence and presence of Ca2+ and Mg2+. The increase in insulin binding was not accompanied by an increase in insulin sensitivity. The lack of effect of ruthenium red on insulin action argued strongly against an increase in intracellular Ca2+ as a potential messenger/transducer of insulin action and suggested that the enhancing effect of Ca2+ on insulin action was a result of increased receptor affinity.
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    The dual effector system for exocytosis in mast cells: Obligatory requirement for both Ca2+ and GTP (1987)
    Springer
    Bioscience reports 7 (1987), S. 369-381 
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    ISSN: 1573-4935
    Keywords: stimulus-secretion coupling ; G-proteins ; mast cells ; calcium ; permeabilised cells ; streptolysin-O ; exocytosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The secretory process is a coordinated cellular response, initiated by occupation of surface receptors and comprising an ordered sequence of biochemical steps subject to multiple controls. Conceptually we can divide the sequence into two main sections comprising early, receptor-mediated events leading to generation of intracellular second messengers, and later events leading to membrane fusion and exocytosis. With the discovery that occupation of Ca2+ mobilising receptors leads to activation of polyphosphoinositide phosphodiesterase (PPI-pde) through the mediation of a G-protein (Gp), all the early events can be ascribed to the plasma membrane. Investigation of the exocytotic stage of secretion has been simplified by the use of permeabilised cells in which the composition of the cytosol can be precisely controlled. We have used streptolysin-O, a bacterial cytolysin which generates protein-sized pores in the plasma membrane, to investigate the exocytotic mechanism of rat mast cells. We find that in addition to the activation of PPI-dpe, GTP also acts in concert with Ca2+ at, or close to, the exocytotic site. Exocytosis can occur after substantial depletion of cytosol lactate dehydrogenase and 3-phosphoglycerate kinase indicating that soluble cytosol proteins are unlikely to play any role. There is no absolute requirement for ATP or phosphorylating nucleotide in exocytosis though when present the effective affinities of the two obligatory effectors (i.e. Ca2+ and GTP) are substantially enhanced.
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    URL: http://dx.doi.org/10.1007/BF01362501
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    Effect of calcium and F-actin on the rate of SH2 modification in skeletal myosin (1987)
    Springer
    Bioscience reports 7 (1987), S. 543-551 
    Details
    ISSN: 1573-4935
    Keywords: calcium ; F-actin ; myosin ; SH2 region
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The rate constant of modification of a specific thiol group, SH2, with N-ethylmaleimide (NEM) has been used to estimate the conformational change in the local area containing SH2 (SH2 region) of skeletal myosin as a structural probe. The rate of Mg2+-ATP-induced SH2 modification of subfragment-1 (S-l) isozymes was regulated by Ca2+ in the pCa range below 6.4 and was not regulated in the pCa range above 6.4. No substantial difference between S-1 containing alkali light chain, A1, (S-1(A1)) and S-1 containing alkali light chain, A2, (S-1(A2)) was observed in the Ca2+-dependent rate of SH2 modification. Due to the presence of this Ca2+ regulation in myosin (absence in S-1 isozymes) in the pCa range above 6.4, absence of 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) light chain in S-1 isozymes, and high affinity of Ca2+ for DTNB light chain, this Ca2+ regulation in the pCa range above 6.4 is possibly related to the Ca2+ binding to DTNB light chain. F-Actin, which is entirely free from tropomyosin and troponin, enhanced the rate of Mg2+-ATP-induced SH2 modification of S-1 isozymes equally and of myosin, and reduced the Ca2+ sensitivity with an increase in F-actin concentration.
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    URL: http://dx.doi.org/10.1007/BF01119770
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    Effects of trypsin on secretion stimulated by micromolar Ca2+ and phorbol ester in digitonin-permeabilized adrenal chromaffin cells (1988)
    Springer
    Cellular and molecular neurobiology 8 (1988), S. 115-128 
    Details
    ISSN: 1573-6830
    Keywords: adrenal gland ; chromaffin cells ; phorbol ester ; digitonin ; secretion ; calcium ; trypsin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Catecholamine secretion from digitonin-treated chromaffin cells is stimulated directly by micromolar Ca2+ in the medium. The permeabilized cells are leaky to proteins. 2. In this study trypsin (30–50µg/ml) added to cells after digitonin treatment completely inhibited subsequent Ca2+-dependent catecholamine secretion. The same concentrations of trypsin did not inhibit secretion from permeabilized cells if trypsin was present only prior to cell permeabilization. 3. The data indicate that trypsin entered digitonin-treated chromaffin cells which were capable of undergoing secretion and that an intracellular, trypsinsensitive protein is involved in secretion. Chymotrypsin was less potent but had effects similar to those of trypsin. 4. The enhancement of Ca2+-dependent secretion from permeabilized chromaffin cells induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) was inhibited by trypsin added simultaneously with Ca2+ to permeabilized cells at concentrations (3–10µg/ml) which had little or no effect on Ca2+-dependent secretion from cells untreated with TPA. Ca2+-dependent secretion in TPA-treated cells was reduced by trypsin only to the level that would have occurred in cells not treated with TPA. Trypsin reduced the large TPA-induced increment of membrane-bound protein kinase C. 5. The data indicate that Ca2+-dependent secretion in the absence of TPA does not require aTPA-like effect of Ca2+ to activate protein kinase C. Protein kinase C activation by TPA probably enhances Ca2+-dependent secretion by modulating the normal Ca2+-dependent pathway or by activating another Ca2+-dependent pathway which functions in parallel to the normal pathway.
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    URL: http://dx.doi.org/10.1007/BF00712917
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    Dual regulation of ACTH secretion by guanine nucleotides in permeabilized AtT-20 cells (1988)
    Springer
    Cellular and molecular neurobiology 8 (1988), S. 129-138 
    Details
    ISSN: 1573-6830
    Keywords: GTP-binding proteins ; calcium ; exocytosis ; guanine nucleotides ; adrenocorticotropic hormone (ACTH) ; AtT-20 cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. We have examined the effects of guanine nucleotides on ACTH secretion from digitonin-permeabilized AtT-20 cells, with the aim of analyzing the involvement of GTP-binding proteins (G proteins) in the secretory process. 2. AtT-20 cells permeabilized with 20µM digitonin displayed calciumdependent secretion. The EC50 of calcium was ~2µM and the maximal stimulation was 350% of basal release. 3. Nonhydrolyzable guanine nucleotides also stimulated ACTH release, in a virtually Ca2+-free medium. The EC50 of guanosine 5′-(3-O-thio)triphosphate (GTP γ S) was ~15µM and the maximal stimulation was ~230% of basal release. The effects of calcium and guanine nucleotides were not additive. 4. In the presence of the inhibitory hormone, somatostatin guanine nucleotides inhibited the calcium-stimulated secretion. 5. Both the stimulatory and the inhibitory effects on secretion of guanine nucleotides were independent of changes in cyclic AMP (cAMP) and calcium. It is suggested that G proteins influence an unknown step in the secretion process, which would be near or at the exocytotic site. 6. The results can be explained by assuming the existence of two types of G proteins, one with stimulatory effects on exocytotic release (GeS) and another with inhibitory effects (GeI).
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    URL: http://dx.doi.org/10.1007/BF00712918
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    Desensitization of the nicotinic acetylcholine receptor: Molecular mechanisms and effect of modulators (1989)
    Springer
    Cellular and molecular neurobiology 9 (1989), S. 141-178 
    Details
    ISSN: 1573-6830
    Keywords: specific desensitization ; nicotinic acetylcholine receptor ; molecular mechanisms ; affinity transitions ; modulators of desensitization ; noncompetitive blockers ; calcium ; substance P ; thymic hormones ; thymopoietin ; thymopentin ; calcitonin gene-related peptide ; receptor phosphorylation ; receptor methylation ; myasthenia gravis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Loss of response after prolonged or repeated application of stimulus is generally termed desensitization. A wide variety of phenomena occurring in living organisms falls under this general definition of desensitization. There are two main types of desensitization processes: specific and non-specific. 2. Desensitization of the nicotinic acetylcholine receptor is triggered by prolonged or repeated exposure to agonists and results in inactivation of its ion channel. It is a case of specific desensitization and is an intrinsic molecular property of the receptor. 3. Desensitization of the nicotinic acetylcholine receptor at the neuromuscular junction was first reported by Katz and Thesleff in 1957. Desensitization of the receptor has been demonstrated by rapid kinetic techniques and also by the characteristic “burst kinetics” obtained from single-channel recordings of receptor activity in native as well as in reconstituted membranes. In spite of a number of studies, the detailed molecular mechanism of the nicotinic acetylcholine receptor desensitization is not known with certainty. The progress of desensitization is accompanied by an increase in affinity of the receptor for its agonist. This change in affinity is attributed to a conformational change of the receptor, as detected by spectroscopic and kinetic studies. A four-state general model is consistent with the major experimental observations. 4. Desensitization of the nicotinic acetylcholine receptor can be potentially modulated by exogenous and endogenous substances and by covalent modifications of the receptor structure. Modulators include the noncompetitive blockers, calcium, the thymic hormone peptides (thymopoietin and thymopentin), substanceP, the calcitonin gene-related peptide, and receptor phosphorylation. Phosphorylation is an important posttranslational covalent modification that is correlated with the regulation and desensitization of the receptor through various protein kinases. 5. Although the physiological significance of desensitization of the nicotinic receptor is not yet fully understood, desensitization of receptors probably plays a significant role in the operation of the neuronal networks associated in memory and learning processes. Desensitization of the nicotinic receptor could also possibly be related to the neuromuscular disease, myasthenia gravis.
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    URL: http://dx.doi.org/10.1007/BF00713026
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    Effects of addition of calcium and magnesium salts on ammonia volatilization during manure decomposition (1989)
    Springer
    Plant and soil 115 (1989), S. 53-58 
    Details
    ISSN: 1573-5036
    Keywords: ammonia volatilization ; calcium ; magnesium ; manure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Ammonia volatilization during aerobic decomposition of poultry manure was significantly reduced through additions of calcium and magnesium salts. The percentage reduction in ammonia loss decreased during the 48 day decomposition period from 85–100% in the first 2–3 weeks, to 23–52% at the end of the experiment. The maximum amount of ammonia which was retained (i.e. maximum reduction in ammonia loss) through addition of the chloride salts of Mg2+ or Ca2+ was independent of the type of cation. However, CaCl2 released some of the ammonia initially retained as production of CO2 and NH3 from the manure decreased after 3 weeks of decomposition, whereas both MgCl2 and MgSO4 did not release any of the initially retained ammonia over the 7 week incubation period. Over the entire incubation period MgCl2 therefore retained more ammonia than CaCl2. Magnesium sulphate was considerably less effective in retaining ammonia than either chloride salts.
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    URL: http://dx.doi.org/10.1007/BF02220694
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    Aluminium and manganese and their relation to calcium in soil solution and needles in three Norway spruce (Picea abies, L. Karst.) stands of Upper Austria (1989)
    Springer
    Plant and soil 114 (1989), S. 257-267 
    Details
    ISSN: 1573-5036
    Keywords: aluminium ; calcium ; manganese ; needles ; soil solution ; spruce ; toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Soil solution and needles of three mature spruce stands in Upper Austria were analysed in order to investigate the uptake and possible toxic effects of Mn and Al, as these two elements become highly mobilised in the soil due to increasing acidity. The Ca/Al molar ratio in the soil solution was below 0.2 in the most damaged stand during almost the whole vegetation period. Despite different dynamics, Al reaches almost identical values in all stands at the end of the vegetation period in both 1-year (current) and 2-year-old needles, respectively. Therefore, needle analysis is not a useful tool for estimation of free Al in the soil. Needle contents of other elements could provide a better information for understanding the forest decline. Mn in the needles correlates significantly with Mn concentrations in the soil solution. As soil Mn will be mobilised by acidic input, Mn needle content can increase to very high levels. Manganese distribution, its interaction with calcium, and possible toxic effects are discussed.
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    URL: http://dx.doi.org/10.1007/BF02220806
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    In situ ion exchange resin bags to estimate forest site quality (1989)
    Springer
    Plant and soil 119 (1989), S. 186-190 
    Details
    ISSN: 1573-5036
    Keywords: ammonium ; calcium ; forest soil ; ion exchange resin ; magnesium ; manganese ; nitrate ; phosphorus ; soil analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Cation and anion exchange resin bags were placed just under the humus layer at five adjacent forest sample sites with differing site quality classes in order to assess the available nutrient supply. For comparison, humus samples were collected from the same sites. Nutrients were extracted from humus samples by conventional extraction methods and by shaking together with ion exchange resin bags. Ca and Mg corresponded best to differences in site quality class, of all analysed ions in thein situ resin bag eluates. Thein situ resin bag adsorption of NH4−N, Na and Mn also showed a positive correlation with site quality. The adsorption of PO4−P was negatively correlated to site quality class. Inadequate amounts of exchange resin, or leaving resin bagsin situ for too long a time result in the replacement of already adsorbed ions by ions with higher ion exchange constants.
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    URL: http://dx.doi.org/10.1007/BF02370284
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    Honeylocust (Gleditsia triacanthos L.) root response to aluminium and calcium (1989)
    Springer
    Plant and soil 119 (1989), S. 181-185 
    Details
    ISSN: 1573-5036
    Keywords: aluminium toxicity ; calcium ; honeylocust ; root biomass ; root branching ; soil acidification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Honeylocust (Gleditsia triancanthos L.) root growth response to varying levels of Al and Ca in soil solutions was examined in two horizons each of two forest soils. With results from all four horizons combined, multiple regression analysis indicated that both Ca and Al were significant (p〈0.01) factors affecting root elongation, branching and biomass production. Over a wide range of Al and Ca concentrations in soil solutions from four different soil horizons, the Ca:Al ratio was a significantly better predictor of honeylocust root response to acid soils than Al or Ca alone.
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    URL: http://dx.doi.org/10.1007/BF02370283
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    Ca2+ interaction with phospholipid bilayers studied by multifrequency phase fluorometry (1989)
    Springer
    Bioscience reports 9 (1989), S. 497-502 
    Details
    ISSN: 1573-4935
    Keywords: calcium ; phosphatidate ; DPH ; phase fluorometry ; distributional analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Calcium interaction with phospholipid membranes containing phosphatidic acid is studied by multifrequency phase fluorometry, using DPH as fluorescent molecule. DPH decay is analysed by a continuous distribution of lifetimes. The results suggest an increase of membrane heterogeneity at low calcium concentrations, without changes in the polarity of the environment surrounding the probe.
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    URL: http://dx.doi.org/10.1007/BF01117053
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    Calcium absorption in man: Some dosing recommendations (1989)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 17 (1989), S. 631-644 
    Details
    ISSN: 1573-8744
    Keywords: calcium ; absorption ; efficiency ; dosing ; regimens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The absorption of calcium involves a saturable (active) and a nonsaturable (passive) component. The work of several investigators indicates that an inverse relationship exists between calcium intake and absorption efficiency. Human calcium absorption data from the literature were analyzed using a model which included both an active and a passive absorption component. Simulations were provided to illustrate the suitability of this model, and another previously reported model, to fit the data and to estimate the absorption efficiency of calcium when using different dosing regimens. Comparisons of the values predicted in this study with some literature values are provided and some assumptions and potential limitations associated with the use of this method are discussed. The division of the daily dose into equal increments taken at equally spaced intervals over the course of the day is recommended as a useful procedure for increasing the absorption efficiency and efficacy of calcium.
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    URL: http://dx.doi.org/10.1007/BF01062122
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    The effect of mineral elements on the maturity of peanut seed (1988)
    Springer
    Plant and soil 106 (1988), S. 263-268 
    Details
    ISSN: 1573-5036
    Keywords: calcium ; lipid ; peanut(Arachis hypogaea) ; potassium ; starch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A greenhouse study was conducted to determine the effect, of certain nutrient elements, on the maturing peanut. Peanut fruits were grown in fruiting zones, which contained a complete nutrient medium, for 15 days. Individual plants were then cultured to maturity whilst allowing the fruit to develop in a nutrient medium which contained the complete nutrient (N, P, K, Ca, Mg and B) from which one element had been excluded. Except in the ‘minus B’ treatment, the basal seed weighed more than 500 mg. In the head seed the “minus Ca” treatment produced the lowest number of seeds which weighed 500 mg or more and P, K and B deficiencies produced not quite such low numbers of seeds above 500 mg. When basal and head seeds were grouped into 3 grades of fresh weights, those from Ca and K deficiencies produced smaller dry weights in seeds harvested on the 80th day. Seeds from a Ca deficient medium had a smaller lipid content and an increased sugar content. The starch content of the seed was decreased by K deficiency.
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    URL: http://dx.doi.org/10.1007/BF02371222
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    Nutrient concentrations in litterfall from some western conifers with special reference to calcium (1987)
    Springer
    Plant and soil 102 (1987), S. 223-227 
    Details
    ISSN: 1573-5036
    Keywords: calcium ; cupressaceae ; leaf litter ; litterfall ; nutrients ; pinaceae ; taxodiaceae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Foliar litterfall nutrient concentrations were analysed for selected members of Taxodiaceae and Cupressaceae families andPseudotsuga menziesii for two arboreta in western Oregon and Washington. Nutrient results between arboreta show similar concentrations with the exception of magnesium, which may be the result of historical land use. Nutrient concentrations between species vary considerably.Pseudotsuga menziesii is particularly distinctive from the Cupressaceae and Taxodiaceae by retaining large amounts of phosphorus and potassium. Taxodiaceae is distinctive by high concentration of Mg while Cupressaceae retains calcium, especiallyChamaecyparis nootkatensis. Results suggest that all members of Taxodiaceae and Cupressaceae retain considerably more Ca than Pinaceae in foliar litter.
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    URL: http://dx.doi.org/10.1007/BF02370707
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    Uptake and distribution of mineral nutrients in muskmelon seedlings under nitrogen and phosphorus stresses and during recovery (1988)
    Springer
    Plant and soil 112 (1988), S. 273-278 
    Details
    ISSN: 1573-5036
    Keywords: calcium ; chlorophyll ; Cucumis melo L. ; magnesium ; plant growth ; potassium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Muskmelon seedlings were grown hydroponically in a greenhouse and starved of nitrogen and/or phosphorus for 4 weeks. They were then transferred to an optimal N and P regime or to the opposite stress for an additional 3-week period. Nitrogen stress reduced markedly N, Ca, and chlorophyll contents of leaves and stems, but increased P content. Phosphorus stress reduced significantly P and K concentrations in stems and leaves but did not affect markedly chlorophyll content and did not result in N accumulation. Both stresses reduced significantly the area of the first leaf mainly by adversely affecting cell division. Repair of N and P concentrations in deficient seedlings by transfer to the optimal nutrition regime was more rapid in N- than in P-stressed seedlings.
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    URL: http://dx.doi.org/10.1007/BF02140006
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    Effect of deicing chloride salts on ion accumulation in spruce (Picea abies (L.) sp.) (1989)
    Springer
    Plant and soil 113 (1989), S. 3-11 
    Details
    ISSN: 1573-5036
    Keywords: calcium ; chlorine ; ion selectivity ; injury ; Picea ; potassium ; retranslocation ; sodium ; uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Among the inorganic chloride salts, NaCl, CaCl2 and in a minor proportion KCl and MgCl2 are used as deicing agents. Mixturs of these salts were merely applied with respect to their physico-chemical properties, but their effect on roadside vegetation has never been studied so far. From a screening of different salt mixtures on ion accumulation in needles and twigs of spruce tress (Picea abies sp.) it was shown that the presence of a small amount of calcium in the salt treatments had some beneficial effects on ion regulation. In the presence of calcium, sodium accumulation could be reduced. But more straightforward was its effect on the selectivity between sodium and potasium in favour of the latter. Chloride concentrations did not alter very much; their role in the presence of monovalent cations is nevertheless obvious and is discussed. The study also confirms the presence of potassium retranslocation in conifer trees. The ion characteristics are briefly discussed with respect to the ecological effects of chloride salts on tress.
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    URL: http://dx.doi.org/10.1007/BF02181915
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    Effects of intermittent waterlogging on the mineral nutrition of cotton (1987)
    Springer
    Plant and soil 101 (1987), S. 211-221 
    Details
    ISSN: 1573-5036
    Keywords: aeration ; calcium ; cotton ; flooding ; magnesium ; manganese ; phosphorus ; potassium ; sodium chloride ; waterlogging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A field experiment was conducted to investigate the effects of intermittent waterlogging on the nutrient status of cotton (Gossypium hirsutum cv. Deltapine 61). The crop was grown in a sloping plot of soil in which a gradient of water-table depth ranging from 0.04m above to 0.60m below the soil surface was established during two periods of waterlogging in mid summer and early autumn. The first waterlogging lasted 8 days; the second lasted 16 days. Dry matter increases were less for severely waterlogged plants than for plants with well-aerated root systems during the first flooding, but the increases were similar during the second. Waterlogging impaired uptake of most nutrients by young plants in the first flooding, but had much less effect on nutrient uptake by older plants in the second. Waterlogging consistently reduced concentrations of P and K in the petioles and laminae of young fully-expanded leaves, and severely waterlogged plants were deficient in these nutrients by the end of the first flooding. Mn did not accumulate to toxic levels in waterlogged plants. During each flooding, waterlogged plants gained in total content of all nutrients studied, but the gains of each nutrient, except for Na, were proportionally smaller than for well-aerated plants. Fluxes of K-, Cl- and HPO4- ions in xylem sap exuded from stumps of detopped plants which had been waterlogged were lower than those from plants with well-aerated root systems. Seed cotton yields and concentrations of nutrients in mature bolls were not affected by the two periods of waterlogging. It is concluded that although intermittent waterlogging induced nutrient stress in cotton plants, especially for P and K in young plants before flowering, they recovered with no detrimental effect upon yield.
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    Effects of switches in nutrient levels during the life cycle of spring wheat (1987)
    Springer
    Plant and soil 103 (1987), S. 199-204 
    Details
    ISSN: 1573-5036
    Keywords: calcium ; growth ; influx ; iron ; magnesium ; nutrient solution ; potassium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Accumulation of cations in roots and shoots and influx of K+(86Rb+) and Ca2+(45Ca2+) into the roots were investigated in spring wheat (Triticum aestivum L. cv. Svenno). Plants were sampled at four main developmental stages: tillering, shooting, heading and grain filling. The effects of switches between a high and a low supply of nutrients were characterized. Growth of the shoots and roots was affected by the switches. A high supply of nutrients at the seedling stage and towards tillering supported a high growth rate, while a further high supply of nutrients increased vegetative growth and delayed grain filling. An early high supply of nutrients followed by a low supply at shooting, heading and grain filling accelerated root growth and growth of the main culm. Switches of the mineral supply gave only small changes in concentration of Mg in the plants. Generally, the K+(86Rb+) influx into the roots decreased during ontogenesis, while Ca2+(45Ca2+) influx increased more or less independent of the switches between nutrients levels.
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    URL: http://dx.doi.org/10.1007/BF02370389
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