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  • Calcium
  • Springer  (172)
  • American Chemical Society
  • Annual Reviews
  • 1985-1989  (74)
  • 1980-1984  (98)
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Year
  • 1
    ISSN: 1436-6215
    Keywords: dietarycalcium ; dietarymagnesium ; dietaryphosphorus ; serumcholesterol ; livercholesterol ; fecalbile acids ; rats ; Calcium ; Magnesium ; Phosphor ; Serumcholesterin ; Lebercholesterin ; Gallensäure im Kot ; Ratten
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Medicine
    Description / Table of Contents: Zusammenfassung Während 28 Tagen wurden an Ratten cholesterinfreie halbgereinigte Diäten, die verschiedene Konzentrationen von Calcium (0,13–0,75 g/100 g), Magnesium (0,02–0,04 g/100 g) oder Phosphor (0,2–0,8 g/100 g) enthielten, verabreicht. Die unterschiedlichen Mineralkonzentrationen hatten keinen Einfluß auf Serum- und Lebercholesterin oder die Ausscheidung von Gallensäuren im Kot.
    Notes: Summary Female rats were fed cholesterol-free, purified diets with different concentrations of calcium (0.13–0.75%, w/w), magnesium (0.02 or 0.04%) or phosphorus (0.2–0.8 %) as the only dietary variable. After 28 days, no effects of the minerals were found on liver cholesterol concentrations and rates of fecal excretion of bile acids.
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  • 2
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    Monatshefte für Chemie 112 (1981), S. 149-156 
    ISSN: 1434-4475
    Keywords: Calcium ; Gallium ; Oxygen ; Single Crystal ; X-Ray
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The hitherto unknown compound Ca3Ga4O9 was prepared and investigated by X-ray single crystal methods. Ca3Ga4O9 has orthorhombic symmetry:a=1435.8;b=1682.5;c=532.1 pm; space group C 2v 11 −Cmm2,Z=6. The tetrahedra network (circles of 4 and 5 GaO4-tetrahedra) and the surrounding of Ca2+ are described and discussed with respect to other oxogallates.
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  • 3
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    Monatshefte für Chemie 119 (1988), S. 1245-1249 
    ISSN: 1434-4475
    Keywords: Azide ; Calcium ; Crystal structure ; Tetramethylammonium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract [N(CH3)4]Ca(N3)3,M=240.29, was prepared from aqueous solutions of tetramethylammoniumazide with calciumazide at 298 K. The crystals are tetragonala=936.6(7) pm,c=694.7(5)pm, space group P4/nmm,Z=2, ρ(x)=1.31Mgm−3. The crystal structure was determined by single crystal x-ray diffraction (234 Mo-Kα-reflections, μ=0.469 mm−1,R=0.064). Calcium is octahedrally coordinated to six azide groups. The octahedra are connected via azide groups to a threedimensional array with the complex ammonium ions between. The terminal nitrogen atoms of the azide groups and the methyl groups are considerably disordered.
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  • 4
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    Monatshefte für Chemie 119 (1988), S. 921-927 
    ISSN: 1434-4475
    Keywords: Azide ; Calcium ; Crystal structure ; Dihydrate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Single crystals of Ca(N3)2·2 H2O have been prepared from aqueous solutions at room temperature. The crystals are monoclinic,a=1 159.0 (3),b=614.2 (2),c=785.5 (2) pm, β=106.52 (2)°,Z=4, space group P21/n. The crystal structure was determined by single crystal X-ray diffraction (1 109 Mo-Kα-reflexions,R=0.052). Calcium atoms are surrounded by four azide groups and four water molecules. The coordination polyhedra are antiprism which are sharing azide groups and water molecules to form layers. The lattice constants and powder pattern agree well with values reported earlier for Ca(N3)2 · 1.5 H2O [1]. It was also shown, that Sr(N3)2 · 2 H2O is isotypic with Ca(N3)2 · 2 H2O.
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  • 5
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    Cellular and molecular life sciences 41 (1985), S. 1551-1552 
    ISSN: 1420-9071
    Keywords: Calcium ; ionophore A23187 ; prostaglandins ; skeletal muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Frog skeletal muscle incubated in vitro with the ionophore A23187 shows extensive morphological alterations. Myofilament disruption, presumably mediated by excess intracellular calcium, can be partially prevented by preincubating the muscle with inhibitors of prostaglandin synthesis and the lysosomal thiol protease inhibitor leupeptin.
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  • 6
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    Cellular and molecular life sciences 43 (1987), S. 1022-1025 
    ISSN: 1420-9071
    Keywords: Calcium ; magnesium ; nematocysts ; Hydra ; Cnidaria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary An X-ray spectral analysis (EDAX) of isolated undischarged nematocysts of various cnidarians (Hydrozoa, Scyphozoa, Anthozoa) revealed the presence of extremely high concentrations of divalent cations. InHydra nematocysts both Ca2+ (conc. 0.36 μmole/mg dry cysts) and Mg2+ (conc. 0.80 μmole/mg dry cysts) ions add up to a total in situ concentration of 0.5 to 1.0 M. More than 85% of the cations, which are believed to be involved in cyst discharge, are contained in the soluble fraction of the cysts, where they must be bound to high molecular weight molecules.
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  • 7
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    BioMetals 2 (1989), S. 161-167 
    ISSN: 1572-8773
    Keywords: Fe chelation ; Thalassemia ; Fe overload ; Calcium ; Magnesium ; Zinc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Formation constants for the calcium(II), magnesium(II) and zinc(II) complexes of the orally effective iron chelator, pyridoxal isonicotinoyl hydrazone (PIH) and three analogues, pyridoxal benzoyl hydrazone (PBH), pyridoxalp-methoxybenzoyl hydrazone (PpMBH) and pyridoxalm-fluorobenzoyl hydrazone (PmFBH) have been determined by potentiometry at 25\dg C andI=0.1 M [KNO3]. The four ligands bind calcium(II) weakly and magnesium(II) only slightly more strongly, as a l: l complex which is formed at pH \s〉 8. The chelation of zinc(II) for all the ligands studied was greater than that for calcium(II) and magnesium(II), with complexation generally becoming significant at about pH 5. Thus, chelation of zinc(II) but not calcium(II) or magnesium(II) at physiological pH, 7.4 may be expected. Calculated values of the concentration of uncomplexed metal ion indicate that the selectivity of these ligands towards Fe(III) is comparable to that of the clinically used chelator desferrioxamine.
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  • 8
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    Calcified tissue international 33 (1981), S. 409-416 
    ISSN: 1432-0827
    Keywords: Bone Cells ; Cyclic AMP ; Calcium ; Parathyroid hormone ; Prostaglandin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary We have examined the influence of extracellular Ca2+ on cyclic AMP metabolism in an osteoblast-enriched population of bone cells isolated from the calvaria of rat fetuses. The cyclic AMP1 response to stimulators of cyclic AMP formation (PTH and PGE2), but not basal cyclic AMP levels, increased progressively as the extracellular Ca2+ concentration was raised from 0.2 to 4.0 mM. The response to changes in extracellular Ca2+ were rapid (within 3.5 min), and the level of responsivity that characterized each Ca2+ concentration persisted for at least 6 h when the Ca2+ concentration was kept constant. The effect of Ca2+ spanned the entire time course of PTH action, was not accompanied by altered excretion of cyclic AMP from the cells, and was evident at low as well as at high hormone concentrations. Ca2+ augmented the action of PTH in the presence as well as in the absence of cyclic AMP phosphodiesterase inhibitors, and failed to decrease cyclic AMP phosphodiesterase activity in the short term. Mn2+ and, to a smaller degree, Ba2+ substituted for Ca2+ in promoting the cyclic AMP response to PTH. Verapamil, an inhibitor of Ca2+ penetration, blunted the Ca2+-mediated increments in the cyclic AMP response, and the divalent cation ionophore A23187 enhanced these increments. These results indicate that Ca2+ and other cations are positive effectors of the stimulated cyclic AMP response in isolated bone cells. Accumulation into an as yet unknown cellular compartment may be required for the cation effect. The data are most consistent with enhancement of adenylate cyclase reactivity as the mode of cation action.
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  • 9
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    Calcified tissue international 30 (1980), S. 209-216 
    ISSN: 1432-0827
    Keywords: Calvarium ; cAMP ; Vitamin D3 metabolites ; Calcium ; Parathyroid hormone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Results from in vitro works suggest that 1,25- and 24,25-dihydroxyvitamin D3 (1,25-(OH)2D3 and 24,25-(OH)2D3) act on bone via different mechanisms. The present investigation was performed to study the effect of these two metabolites and of their precursor 25-hyxdroxyvitamin D3 (25-(OH)D3) on bone cAMP content in vitro. Rats' paired half calvaria were incubated under sterile conditions with one vitamin D3 derivative (10−13 to 10−9 M) or with ethanol (0.005 ml for 15 min to 24 h in 1 ml medium containing 0, 0.2, 1, 2, or 3 mM calcium. In some experiments: (a) cycloheximide (10−5M) was added simultaneously with the vitamin D3 metabolites; (b) 1–84 bPTH (5 × 10−8 M) was added for 5 or 15 min at the end of the 24 h incubation. Calvaria were immersed in 1 ml TCA 5% 4°C and homogenized. The cAMP was extracted with diethylether and measured by a competitive protein binding assay. Results bring further evidence for a particular effect of low doses of 24,25-(OH)2D3 (10−9 to 10−12M) and of 25-(OH)D3 (10−9 to 10−11M) on bone, different from that of 1,25-(OH)2D3: cAMP content was higher in 24,25-(OH)2D3- or 25-(OH)D3-treated and lower in 1,25-(OH)2D3-treated calvaria than in ethanol-treated ones with 1 mM calcium. The 1,25-(OH)2D3 effect persisted in calcium-free medium whereas 25-(OH)D3 and 24,25-(OH)2D3 effects could not be observed with 0 mM nor with 3 mM calcium. The required duration of the preincubation (over 1 h) as well as the inhibitory action of cycloheximide may suggest an involvement of protein synthesis in the vitamin D3 metabolites effects. Neither 1,25-(OH)2D3 nor 24,25-(OH)2D3 affected the PTH-induced increase in bone cAMP content.
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  • 10
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    Calcified tissue international 32 (1980), S. 201-206 
    ISSN: 1432-0827
    Keywords: Magnesium ; Parathyroid hormone ; Secretion ; In vitro ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary In a well-defined in vitro perifusion system, the effects of extracellular magnesium concentration (Mg) on parathyroid hormone (PTH) secretion by bovine parathyroid tissue were examined. At Mg less than 0.8 mM, the ability of the glands to secrete hormone maximally in response to low calcium (Ca) stimulation was progressively impaired. Low Mg also impaired the ability of isoproterenol, dibutyryl cyclic AMP and theophylline to stimulate hormone release. The defect in hormone release at low Mg observed in vitro was analogous to the well-documented inhibition of secretion observed in vivo. Increases in Mg from 0 to 0.8 mM rapidly repaired the defect in hormone secretion. At Mg above 1.0 mM there was a Ca-like effect on hormone release, with a progressive decrease in secretion at increased Mg. Although its mechanism is not yet clear, the low Mg effect appears to impair principally the process of hormone release rather than its biosynthesis or storage.
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  • 11
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    Calcified tissue international 36 (1984), S. 139-144 
    ISSN: 1432-0827
    Keywords: 1,25(OH)2-vitamin D ; Weight loss ; Phosphate ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary During a review of 42 metabolic studies in healthy women and men we observed that serum 1,25-(OH)2-D concentrations were directly correlated to the observed daily changes in body weight (r=0.68;P〈0.001) and to caloric intake/kg/day (r=0.39;P=0.01). These relationships could not be accounted for by related and physiologically expected changes in serum Ca or iPTH concentrations. However, serum 1,25-(OH)2-D concentrations were observed to be inversely correlated to serum PO4 levels (r=−0.44;P=0.004). In addition, serum PO4 levels were inversely correlated to the daily changes in body weight (r=−0.40;P=0.009). Since dietary sodium intake averaged 142 mmol/day, it is unlikely that the observed changes in weight were the result of changes in salt and water balance. Thus it seems reasonable to speculate that serum 1,25-(OH)2-D concentrations may vary directly with energy balance, as reflected by changes in body weight. This effect may be mediated by alterations in PO4 metabolism. The accurate assessment of serum 1,25-(OH)2-D levels thus appears to require several measurements over time periods during which body weight is stable.
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  • 12
    ISSN: 1432-0827
    Keywords: Electromagnetic field ; Bicarbonate ; Phosphate ; Calcium ; Fluoride ; Osteogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The present studies are aimed at establishing molecular correlations in the interaction of very low frequency electromagnetic fields with biological systems. Ca-uptake by chick embryo tibia rudiment in short-term culture was a useful model. Tibiae of 8- to 10-day-old chick embryos were incubated 60 min in simplified culture media in the presence of45Ca at 37.5±0.5°C either inside or outside pulsating electromagnetic fields. Radioactivity count in the medium was the most accurate method for determining Ca-uptake by the rudiment. The effect of the fields on the Ca-uptake depended markedly on the chemical composition of the culture medium: bicarbonate was indispensable; glucose or sucrose was important; phosphate was potentiating; ethanol, Mg2+, and NaF were stimulating. The field had no effect in (a) blank medium without tibia, (b) tibiae that had been altered by fixation with aqueous glutaraldehyde, (c) nonliving artificial systems endowed with great or small ion sorption capacity. The unique bicarbonate effect with living systems and the passive behavior of nonliving ion sorbing systems prompt the suggestion that the electromagnetic field probably couples with specific processes, such as a bicarbonate-dependent Ca2+ ATPase and the active ion transport, at the cell membrane level. The molecular mechanisms remain to be established.
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  • 13
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    Calcified tissue international 36 (1984), S. 194-199 
    ISSN: 1432-0827
    Keywords: Benzo(B)Thiophene-2-Carboxylic Acid ; Bone cells ; Calcium ; Cyclic AMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The purpose of the present study was to investigate the mechanism of action on bone of Benzo(B)Thiophene-2-Carboxylic Acid (BL-5583). BL-5583, at a dose range of 0.01–100 µg/ml, inhibited spontaneous as well as A23187 and PTH-induced bone resorption in tissue culture. This compound also decreased calcium uptake in both osteoclastic and osteoblastic enriched bone cell populations obtained by sequential collagenase digestion of 1–2 day newborn rat calvariae. The decrease occurred after a 5 min. incubation with45Ca and BL-5583. The effective dose range was 0.01–100 µg/ml. No effect on leucine incorporation or lactic acid production by bone cells was observed. BL-5583 also induced a transient decrease in calcium uptake in skin cells isolated from fetal rats by collagenase digestion, suggesting a lack of tissue specificity for this compound. No effect on cyclic AMP in isolated bone cells was observed with the same dose range that produced a calcium effect.
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  • 14
    ISSN: 1432-0827
    Keywords: Saliva ; Calcium ; Phosphate ; Ion-binding ; Supersaturation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Previous ultrafiltration studies indicated that up to one-half of the calcium and two-thirds of the phosphate in human salivary secretions may be bound by salivary proteins. Since this binding is an important variable in determining the extent of salivary supersaturation with respect to calcium phosphate salts, and since the amount of binding reported is surprisingly large, calcium and phosphate ion-binding by salivary macromolecules has been reexamined. From experiments using equilibrium dialysis, it was found that (1) the fraction of salivary calcium involved in macromolecular complexes ranges from a few percent for unstimulated secretions, to no more than about 10% for stimulated glandular salivas, and (2) salivary proteins do not bind phosphate ions to any significant extent. These findings, and experiments using an improved ultrafiltration membrane, indicate that the earlier results were artifacts of the ultrafiltration technique. Fractionation of salivary proteins, followed by equilibrium dialysis measurements, showed that the anionic proline-rich proteins and a basic proline-rich glycoprotein are responsible for most of the calcium binding now observed. The finding that macromolecular complexes of salivary calcium and phosphate have been overestimated in the past, leads to the conclusion that salivary calcium and phosphate ion activities in stimulated salivary secretions may be up to 50 to 100% higher than previously thought. Revised values were therefore used to recalculate the degree of salivary supersaturation with respect to calcium phosphate salts. The results indicate that stimulated salivary secretions are supersaturated with respect to dicalcium phosphate dihydrate; this is a substantially greater degree of supersaturation than previously reported.
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  • 15
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    Trees 2 (1988), S. 65-72 
    ISSN: 1432-2285
    Keywords: Calcium ; Chlorine ; Ion shifts ; Mimosa pudica ; Potassium ; Seismonastic movements ; X-ray microanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Using energy-dispersive X-ray microanalysis, the concentrations of ions, especially potassium and chlorine, were determined in different tissues of primary and tertiary pulvini of Mimosa pudica. It was shown that stimulating the leaf was followed by ion displacements which were most striking in the outer extensor cells, resulting in turgor loss. Since Ca concentration remains relatively constant in cell walls of collapsed cells, the changes of K concentration are best described by the K:Ca ratio. After stimulation the K:Ca ratio dropped in the outer extensor of the primary pulvinus from 775.3 to 2.37 in the cytoplasm, and from 542.2 to 9.25 in the cell wall. Changes in chlorine content were less striking in the primary pulvinus. The K∶Cl ratios in some cases were lower than 1.0, which indicates that Cl content can increase, while K content is diminished. In the non-stimulated tertiary pulvini the outer extensor cells show high concentrations of Cl, but much lower Cl concentrations were found after stimulation. In contrast to the primary pulvinus the K content of the tertiary pulvini is very low. In the vascular tissues of both primary and tertiary pulvini stimulation is followed by a release of K and Cl out of the sieve element cytoplasm into the apoplast. K then appears accumulated in the cell walls of the collenchymatous tissue. These displacements lead to the assumption that the collenchymatous apoplast temporarily functions as a reservoir for K and to a lesser extent for Cl. With regard to the mechanism of leaf movement after stimulation, the accumulation of ions in the apoplast seems to be initiated by the decrease of water potential triggered by an apoplastic accumulation of unloaded sucrose (Fromm and Eschrich 1988a). The resulting turgor release in the outer extensor is accompanied by an efflux of ions.
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  • 16
    ISSN: 1432-2285
    Keywords: Aluminum ; Calcium ; Fine roots ; Microbeam analysis ; Picea abies ; Soil acidification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A novel stable isotope labelling procedure for microbeam analysis was developed to monitor exchange and uptake of nutrients, primarily Mg, K and Ca, by root tips at the cellular level. Initially root samples were analysed from 2-year-old spruce trees, originating both from a nursery and from a polluted forest site, (1) for the cortex cell wall accessibility and nutrient binding properties, (2) for the influence of low pH and elevated aluminum concentrations on Ca binding to cortex cell walls, and (3) for long-range transport into the secondary xylem, proximal to the labelled root tip. In nursery control plants, Ca is localized mainly in the apoplast of the cortex. Exchange of Mg, K, Ca in the cell wall of the cortex and the primary xylem with label in incubation solutions is almost completed to equilibration within 30 min. In the secondary xylem we could detect Mg, K, and Ca from labelling solutions in minute amounts after 30 min, and as a major fraction after 48 h. This indicates that stable isotope labelling can be used to study both ion-exchange properties of the apoplast and long-range transport. Slight acidification of the labelling incubation media to pH 4.5 reduced Ca binding to the cortex cell walls slightly, but acidification to the extreme value of pH 2.3 reduced binding 41%. A combination of pH 4.5 and increased free aluminum reduced the binding by 83%. In a preliminary attempt to analyse the nutrient binding capability of the root-tip apoplast from pollution affected trees, we exposed fine roots of 2-year-old spruce from an acidified and polluted site showing typical low levels of Ca and Mg in the cortical cell walls to Ca-enriched media. Under these conditions the Ca content of cortex cell walls doubled upon incubation at pH 4.7, reaching 40% of the total binding capacity of our nursey control plants.
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  • 17
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    Monatshefte für Chemie 118 (1987), S. 567-572 
    ISSN: 1434-4475
    Keywords: Azide ; Calcium ; Crystal structure ; Pyridine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Diazido-dipyridine-calcium was prepared by the reaction of Ca(N3)2 with pyridine. The crystals are tetragonal, space group I $$\bar 4$$ 2 m (121),N=2,a=699.7 (1),c=1 450.6 (5) pm. The crystal structure was determined by single crystal X-ray diffraction, 415 independent observed Mo-Kα-counter reflexions,R=0.049. The calcium atoms are sixcoordinated to four nitrogen atoms of azide groups and to two nitrogen atoms of pyridine. The coordination polyhedra are tetragonal bipyramids which are linked together by four azide groups to form sheets of composition Ca(N3)2. The pyridine rings are directed perpendicular to the sheets.
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  • 18
    ISSN: 1432-041X
    Keywords: Phorbol ester ; Muscarinic receptor ; Calcium ; Chick embryo ; Morphogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A muscarinic cholinergic receptor is present on undifferentiated cells of the chick embryo. Stimulation of the muscarinic receptor with muscarinic agonists triggers intracellular Ca2#x002B; mobilization. Here, we investigate the effect of phorbol 12-myristate 13-acetate (PMA) on the muscarinic receptor-mediated Ca2#x002B; mobilization, which is monitored in cell suspensions of chick embryos of stage 24 by chlorotetracycline fluorescence. PMA inhibits the Ca2#x002B; mobilization in a time-dependent and concentration-dependent manner without changing the ED50 of acetylcholine. The concentration of PMA that gives halfmaximal inhibition is 3.1×10−9 M PMA.
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  • 19
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    Cellular and molecular life sciences 41 (1985), S. 1328-1330 
    ISSN: 1420-9071
    Keywords: Calcium ; cholesterol supersaturation ; lithogenicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Analog bile supersaturated with cholesterol was constituted, filtered and divided into equal portions containing no calcium or calcium, 2.5–15 mM. Aliquots were removed over the next 48 h and filtrates analyzed for cholesterol, bile acid and lecithin. Calcium accelerated cholesterol loss from solution in a dose-related fashion.
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  • 20
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    Cellular and molecular life sciences 44 (1988), S. 97-100 
    ISSN: 1420-9071
    Keywords: Calcium ; platelet ; second messenger
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Experiments with permeabilised platelets, and with intact platelets loaded with fluorescent Ca2+-indicators, over the past several years have greatly extended our knowledge and understanding of cytosolic Ca2+ as a platelet activator and its interactions with other cytosolic regulators. This article outlines insights, gained from the use of the fluorescent dyes, into maintenance and restoration of basal [Ca2+]i, mechanisms of receptor-mediated Ca2+-mobilisation and quantitation of [Ca2+]i/response relations in intact human platelets.
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  • 21
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    Cellular and molecular life sciences 45 (1989), S. 407-413 
    ISSN: 1420-9071
    Keywords: Calcium ; inositol phospholipids ; Ca++ channels ; Ca++/Mg++-ATPase ; dihydropyridine receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Studies have implicated Ca++ in the actions of ethanol at many biochemical levels. Calcium as a major intracellular messenger in the central nervous system is involved in many processes, including protein phosphorylation enzyme activation and secretion of hormones and neurotransmitters. The control of intracellular calcium, therefore, represents a major step by which neuronal cells regulate their activities. The present review focuses on three primary areas which influence intracellular calcium levels; voltage-dependent Ca++ channels, receptor-mediated inositol phospholipid hydrolysis, and Ca++/Mg++-ATPase, the high affinity membrane Ca++ pump. Current research suggests that a subtype of the voltage-dependent Ca++ channel, the dihydropyridine-sensitive Ca++ channel, is uniquely sensitive to acute and chronic ethanol treatment. Acute exposure inhibits, while chronic ethanol exposure increases45Ca++-influx and [3H]dihydropyridine receptor binding sites. In addition, acute and chronic exposure to ethanol inhibits, then increases Ca++/Mg++-ATPase activity in neuronal membranes. Changes in Ca++ channel and Ca++/Mg++-ATPase activity following chronic ethanol may occur as an adaptation process to increase Ca++ availability for intracellular processes. Since receptor-dependent inositol phospholipid hydrolysis is enhanced after chronic ethanol treatment, subsequent activation of protein kinase-C may also be involved in the adaptation process and may indicate increased coupling for receptor-dependent changes in Ca++/Mg++-ATPase activity. The increased sensitivity of three Ca++-dependent processes suggest that adaptation to chronic ethanol exposure may involve coupling of one or more of these processes to receptor-mediated events.
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  • 22
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    Calcified tissue international 32 (1980), S. 229-236 
    ISSN: 1432-0827
    Keywords: Bone ; Ion influxes ; Calcium ; Phosphate ; Exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Quantitative measurements were made of the ion fluxes of calcium and phosphate into and from calvaria (mouse or rat) when clamped in specially designed micro-Ussing chambers. The effects of varying concentrations of calcium were examined on the influx and efflux of calcium and of its counterion, phosphate. A comparable series of experiments was performed with varying phosphate concentrations. Both ions, as their concentrations increased, depressed their own influx, increased their own efflux, and significantly increased the equilibrium concentration, E/K, supported by the calvaria. Similarly, both ions, as their concentrations increased, affected the influx or efflux of their counterion only slightly but did depress the counterion's equilibrium level, E/K, significantly. In spite of these changes it was shown that calvaria effectively buffered the medium at physiological concentrations of calcium and phosphate. The buffering capacity, however, was small, and the balance, E/K, was modified by small uptake or loss of either ion. The small size of the interacting mineral pool was confirmed by direct measurement of the rapidly exchanging fractions of both calcium or phosphate. They were only ∼1% of the total ions present. The significance of these findings is discussed.
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  • 23
    ISSN: 1432-0827
    Keywords: Calcium ; Vitamin D deficiency ; 1,25(OH)2D3 ; Parathyroidectomy ; Parathyroid hormone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Studies presented here were designed to investigate further the basis for an impaired cAMP response to parathyroid hormone (PTH) in osteoblastlike calvarial bone cells isolated from vitamin D-deficient rat pups. The goal was to perturb Ca, PTH, and vitamin Din vivo in order to see which factors might be responsible for the impairedin vitro bone cell cAMP response. Pups either were parathyroidectomized (PTX) 3–5 days, implanted with osmotic minipumps delivering high doses of PTH, given repeated, high doses of 1,25(OH)2D3, or were D-deficient (-D, i.e., born and suckled by D-deficient mothers). Osteoblastlike bone cells, isolated by sequential enzyme digestion and centrifugation, were exposed to PTH for 5 min in the presence of a phosphodiesterase inhibitor. In bone cells isolated from -D rat pups, both basal and PTH-induced cAMP accumulation were significantly lower than in +D bone cells. Earlier, we had shown that two daily injections of -D pups with 50 ng 1,25(OH)2D3 restores this reduced bone cAMP response of -D pups toward normal. In the present study, neither basal nor PTH-induced bone cell cAMP accumulation was affected by subjecting D-replete pups to PTX, PTH infusion, or repeated high doses of 1,25(OH)2D3 despite the fact that each treatment markedly changed serum Ca or serum immunoreactive PTH. The results indicate that the impaired bone cell cAMP response seen in -D pups is not a direct result of chronic hypocalcemia and that the “heterologous desensitization” seenin vitro with added 1,25(OH)2D3 could not be duplicated byin vivo treatment of +D pups with supraphysiologic doses of 1,25(OH)2D3. Finally the lack of alteration in the bone cell cAMP response to PTHin vitro after chronic PTH infusionin vivo fails to support the notion that the impaired response in -D bone cells can be explained entirely by “homologous desensitization” induced by high circulating levels of PTH in the hypocalcemic, -D rat pup.
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  • 24
    ISSN: 1432-0827
    Keywords: Calcitonin ; Parathyroid hormone ; Calcium ; Newborn ; Fracture
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    Topics: Biology , Medicine , Physics
    Notes: Summary Determinations of serum calcium (Ca), phosphorus (P), calcitonin (CT), and parathyroid hormone (PTH) were carried out in 36 full-term newborn infants with fracture of the clavicle (CF) and in 46 normal neonates (N). At the 6th hour of life the CF neonates demonstrated lower serum Ca and higher serum CT in comparison with normal infants. In the hours following, no significant differences between the two groups for the Ca levels were found, whereas serum CT remained significantly higher in the CF newborns at the 24th, 48th, and 72nd hour of life. Significant differences between normal and CF infants in the PTH serum levels were detected only at the 48th hour, when PTH was lower in the CF newborns. The results of this investigation indicate that the fracture of the clavicle is a significant and peculiar factor in stimulating CT secretion. Serum Ca level appeared to be controlled by CT rather than auto-regulating the secretion of the hormone.
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  • 25
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    Calcified tissue international 33 (1981), S. 365-368 
    ISSN: 1432-0827
    Keywords: Absorptiometry ; Osteoporosis ; Spinal bone ; Bone mineral content ; Neutron activation ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Dual-photon absorptiometry using153Gd (44 and 100 keV) was used to measure the bone mineral content (BMC) of the trunk and of the total body (TBBM) in 7 volunteers with no overt bone disease. These values were compared to those obtained with partial-body neutron activation of calcium (trunk Ca). The trunk Ca seemed to represent best a 60 × 30 cm area; the correlation coefficient with the corresponding BMC in that area was 0.97 (SEE ⋍ 7%). Trunk Ca was also highly correlated with TBBM (r=0.96; SEE=8%) and with radius BMC (r=0.92; SEE=11%), but the correlations with the BMC of smaller subareas of the trunk were lower (r⋍0.9; SEE ∼ 12%). The BMC of the lumbar spine was only moderately correlated with trunk Ca, radius BMC and TBBM (r ∼ 0.82; SEE ∼ 18%), and only slightly more associated with trunk BMC (r ∼ 0.88; SEE ∼ 14%). The BMC of the combined lumbar-thoracic spine showed higher correlations with trunk Ca, radius BMC and TBBM (r ∼ 0.87; SEE ∼ 13%), and trunk BMC (r=0.93; SEE ∼ 10%). An accurate and sensitive measure of spinal status requires a direct measurement of that area.
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  • 26
    ISSN: 1432-0827
    Keywords: Bone cells ; Cyclic AMP ; Calcium ; Ascites fluid resorptive protein
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    Topics: Biology , Medicine , Physics
    Notes: Summary The effects of a bone resorptive protein isolated from human cancer ascites fluid on bone cell calcium and cyclic AMP were studied with fetal rat cells. The osteoclast-activating factor increased bone cell calcium uptake at 37°C and 4°C with no direct effects on calcium efflux. Concentrations of the resorptive factor that increased in vitro bone resorption and cell calcium uptake had no effect on cyclic AMP. The effects of the protein on calcium uptake were not specific for bone cells, and large increases were also observed in isolated fetal rat skin cells. These studies suggest that increases in the permeability of the cell membrane to calcium are involved in the mechanism of action of the ascites fluid resorptive protein.
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  • 27
    ISSN: 1432-0827
    Keywords: Hydroxyapatite ; Dissolution ; Pyrophosphate, Diphosphonates ; Calcium ; Phosphate
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    Notes: Summary Pyrophosphate and diphosphonate ions have been said to diminish the dissolution of hydroxyapatite crystals, because they lower the equilibrium concentrations of calcium and phosphate ions in the bulk solution around hydroxyapatite crystals in a closed system. However, in a closed system these effects are not necessarily due to an effect on dissolution alone. In this paper we have used a continuous flow system to study the effects of pyrophosphate and two diphosphonates, ethane-1-hydroxy-1,1-diphosphonate and dichloromethane diphosphonate, on the dissolution of hydroxyapatite. All three compounds decreased markedly the rate of dissolution of hydroxyapatite as well as the exchangeable pools of calcium and phosphate ions around the cystals.
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  • 28
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    Calcified tissue international 31 (1980), S. 231-238 
    ISSN: 1432-0827
    Keywords: Magnesium ; Bone ; Calcium ; Parathyroid gland
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    Topics: Biology , Medicine , Physics
    Notes: Summary Calcium homeostasis and bone pathology were studied in weanling rats fed a low (70 ppm) magnesium diet for 2–21 days. The rats developed significant, progressive hypercalcemia after 6 days on the diet. The increase in blood calcium was accompanied by progressive hypoactivity of the parathyroid gland (PTG), as determined by histologic and morphometric analyses. Thus hyperactivity of the PTG could not have been responsible for the hypercalcemia observed. Histologic examination of femora and humeri from magnesium-deficient rats showed progressive subperiosteal hyperplasia, consisting of undifferentiated osteoprogenitor cells and fibrous tissue, after 7 days of deficiency. The presence of unmineralized osteoid tissue in the metaphyses indicated that mineralization was not proceeding normally. The alterations in differentiation of osteoprogenitor cells, together with the failure of mineralization, resulted in significantly lower rates of bone formation (as measured by fluorochrome labeling) in the magnesium-deficient rats. Basophilic cementing lines and inactive osteocytes in the cortices of bones from magnesium-deficient rats indicated that bone resorption was also severely reduced in magnesium deficiency. We postulate that bone magnesium depletion (66% by day 21) has a direct negative effect on osteoblastic and osteocytic activity, and may explain, in part, the decreased responsiveness of bone to parathyroid hormone (PTH) that has been observed in magnesium-deficient animals.
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  • 29
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    Calcified tissue international 32 (1980), S. 45-53 
    ISSN: 1432-0827
    Keywords: Dentin ; Periodicity ; Allometry ; Calcium ; Sulfur
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    Topics: Biology , Medicine , Physics
    Notes: Summary We have described differences in the aspects of biological rhythms for calcium and sulfur deposition on the labial and lingual sides of the growing rabbit incisor, where growth occurs along a spiral axis. The calcium oscillations appear to be smoother on the labial side than on the lingual side. The lingual side is characterized by high-frequency rhythms with high amplitudes which possess the greatest percent of the power (Fourier analysis). These observations also reflect a difference in behavior of the mean Ca concentration across the labial and lingual sides. Sulfur rhythms on the labial side have higher amplitudes than those on the lingual side, but systematic differences in distribution of power between high and low frequencies is not as pronounced as in the case of Ca. The differences in Ca rhythms reflect differences in the growth rates of incisors on either side of the spiral axis. The labial side grows slightly faster than the lingual side, and its odontoblasts secrete Ca along the spiral axis and toward the pulp cavity at the same time. Thus the resultant direction of growth is more nearly opposite the extension of the occlusal end on the labial side, and Ca is consequently deposited over a wider area relative to that on the lingual surfaces. On the lingual side, Ca is deposited within a more limited area, and growth must therefore be continuous at high frequencies. The distribution of Ca on both sides of the tooth reflects these differences in growth rate and periodicity in two ways. First, given a unit area of tooth, the calcium concentration on the labial side is less than that of the lingual side. Second, whereas the calcium concentration on the labial side declines rapidly from the enamel-dentin junction to the pulp cavity, it is uniformly high across the lingual side because its growth is more continuous at high frequencies.
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  • 30
    ISSN: 1432-0827
    Keywords: 1α-Hydroxy vitamin D3 ; 1,25-Dihydroxyvitamin D3 ; Calcium ; Transport ; Intestine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The timed sequence of events following the oral administration of 1α-hydroxy vitamin D3 (1αOHD3) to rachitic chicks was compared to that following a comparable dose of 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3). RNA polymerase activity was maximally increased 20% by 1αOHD3 within 1 to 2 h and returned to control values after 8 h. Alkaline phosphatase activity was stimulated by 4 h and was maximal (3- to 5-fold increase) at 24 h. Calcium binding protein (CaBP) was detected initially within epithelial cells at the proximal end of the villus (just above the crypt) 6 to 8 h after 1αOHD3 administration, in epithelial cells lining the proximal half of the villus by 24 h, and in epithelial cells along nearly the entire villus by 48 h. At no time did goblet cells contain CaBP. Serum calcium concentrations were significantly elevated in 2 h and maximal by 12 h (an increase of 3.6 mg/dl). Calcium accumulation by the intestinal mucosa in vitro was increased by 6 to 8 h and maximal (60% increase over controls) at 24 h. Phosphate accumulation by the intestinal mucosa in vitro was increased by 6 h and maximal (105% increase over controls) between 8 and 24 h. 1,25(OH)2D3 increased CaBP and calcium accumulation by 4 h, 2 h sooner than did 1αOHD3. 1,25(OH)2D3 decreased serum calcium levels and increased serum phosphate levels at 2 h unlike 1αOHD3. No difference in the effects of these compounds on alkaline phosphatase activity, RNA polymerase activity, and phosphate accumulation could be demonstrated. These results are consistent with the possibility that 1αOHD3 may not require conversion to 1,25(OH)2D3 for all of its biological effects.
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  • 31
    ISSN: 1432-0827
    Keywords: Perifusion ; Parathyroid hormone ; In vitro ; Calcium ; Beta regulation
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    Notes: Summary An in vitro perifusion system was used to study parathyroid hormone (PTH) secretion in response to calcium (Ca) and beta-adrenergic agents. Perifused parathyroid tissue responded to changes in Ca within the physiologic range during experiments up to 5 h. There was rapid secretory stimulation after exposure to low Ca, with the maximum response being observed at 20 min. Normal bovine glands showed a Ca-independent nonsuppressible component of PTH release at concentrations of Ca above physiologic. 1-isoproterenol produced rapid stimulation of PTH release, the response being blocked by a beta antagonist. The maximum secretory response to either low Ca (0.5 mM) or 1-isoproterenol (10−5 M) was enhanced when the two stimuli were applied simultaneously. The response to isoproterenol was blocked by raising Ca to 2.5 mM. Although d,l-propranolol (10−4 M) caused mild suppression of PTH release at a Ca of 1.25 mM, it did not cause additional suppression at 2.5 mM Ca nor did it decrease the response to 0.5 mM Ca stimulation. The secretory response of the gland to low Ca was sustained at a level more than double the baseline rate. The response to isoproterenol was more transient, with a return to or toward baseline secretion within 60 min. These results suggest that beta agonists and low Ca have separate but related mechanisms for stimulating PTH release and may affect different pools of hormone. The perifusion system described is a relatively simple technique for assessing the kinetics and interactions of various stimulators of PTH secretion.
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  • 32
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    Calcified tissue international 32 (1980), S. 29-44 
    ISSN: 1432-0827
    Keywords: Rabbit ; Dentin ; Calcium ; Sulfur ; Periodicity ; Circadian ; Ultradian
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary We have identified a variety of biological rhythms involved in the apposition and mineralization of dentin in the rabbit incisor. Animals were injected during the day or night with lead acetate at 2-week intervals—to provide biological time markers in forming dentin—and transverse undecalcified sections of the lower incisors were prepared for electron microprobe analysis. The positions of the lead markers were identified, and the continuous distribution of calcium and sulfur was measured at 1 µm intervals between the markers. In thin sections stained with hematoxylin after decalcification, the widths of a series of structural increments (bands) were measured with an ocular micrometer. Fourier analysis of the data revealed spectra of structural and compositional rhythms with a range of periodicities which extended from a matter of hours [ultradian (〈24 h)] to days [infradian (〉24 h) and circadian (approximately 24 h)]. The structural and compositional rhythms appeared to be independent to the extent that they did not necessarily have the same periods, or amplitudes. Nor were there simple phase relationships between all of the rhythms. At some times, Ca and S fluctuations are inversely proportional (180° out of phase), but in other cases they are directly proportional or out of phase by varying degrees other than 180°. The analyses thus suggest that calcium and sulfur deposition (representing mineral and glycosaminoglycan deposition, respectively) are not simply inversely proportional, and that the hematoxylin-stained structural increments did not solely reflect differences in the distribution of the mineral components in dentin.
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  • 33
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    Calcified tissue international 34 (1982), S. 253-257 
    ISSN: 1432-0827
    Keywords: Prednisolone ; Calcium ; Bone ; Corticoid osteopenia ; Vitamin D metabolites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Adult male rats were fed a diet containing 0.15% calcium, 0.3% phosphorus, and either 100, 50, or 20 mg of prednisolone per kg of diet. All these levels of prednisolone led to osteopenia, decreased intestinal absorption of calcium, slightly lower serum calcium and phosphorus, and a decreased level of serum 1,25-dihydroxyvitamin D3. Exogenous parenteral 1,25-dihydroxyvitamin D3 corrected steroid-induced changes in serum calcium and phosphorus, but could not completely correct the low intestinal calcium transport; nor did it prevent the development of osteopenia. The prednisolone-induced osteopenia seems at least in part to be caused by impaired intestinal calcium transport. The impaired calcium transport may be the result of low levels of 1,25-dihydroxyvitamin D3 and a direct effect of presnisolone on the intestine.
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  • 34
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    Calcified tissue international 36 (1984), S. 596-603 
    ISSN: 1432-0827
    Keywords: Calcium ; Ameloblasts ; X-ray microanalysis ; Transport ; Frozen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Energy dispersive X-ray microanalysis was applied to freeze-dried blocks of enamel organ tissue to determine levels of calcium in various celular regions. The tissue blocks were dissected free from adjacent forming enamel following injection of cobalt or fluoride ions, both of which temporarily inhibit enamel mineralization. In all control and experimental specimens there was an increasing gradient of calcium from the stratum intermedium cells to the distal ends of the ameloblasts. Calcium levels were significantly reduced near the distal ends of the ameloblasts following cobalt or fluoride injection as compared with controls. It is suggested that evidence of an intercellular buildup of calcium near the distal ends of the ameloblast supports a controlling function of these cells. The changes in calcium levels are correlated with alterations in mineralization known to occur in the adjacent enamel of the model systems employed.
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  • 35
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    Calcified tissue international 33 (1981), S. 477-484 
    ISSN: 1432-0827
    Keywords: 1,25-(OH)2-D ; Calcium ; Phosphorus ; Sex ; Age
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Dietary phosphate deprivation in women, but not men, is accompanied by a fall in plasma PO4 and a rise in plasma 1,25-(OH)2-vitamin D concentrations. In contrast, young male rats exhibit a fall in plasma PO4 and a rise in plasma 1,25-(OH)2-D concentrations in response to PO4 deprivation. To evaluate whether age and sex influence basal plasma 1,25-(OH)2-D levels and their regulation by PO4 deprivation, plasma 1,25-(OH)2-D, PO4, and Ca levels were measured in male and female rats ranging in age from 6 weeks to 6 months while they were eating normal or low PO4 diets for 1 to 16 days. Similar observations were also made in 6-week-old castrated male and female rats, males replaced with testosterone, and females replaced with estradiol. Basal plasma 1,25-(OH)2-D levels were higher in 6-week-old males (228±76 pmol/l) than in 6-week-old females (148±62 pmol/l;P〈0.01) and declined by age 11 weeks to stable levels averaging about 100 pmol/l without sex difference. Dietary PO4 deprivation resulted in a three-to fourfold increase in plasma 1,25-(OH)2-D concentrations regardless of age and sex, accompanied by a correlated rise in serum Ca concentrations. Castration of 6-week-old males and females eliminated the sex difference in basal plasma 1,25-(OH)2-D levels and appeared to enhance the elevation of plasma 1,25-(OH)2-D concentrations in response to PO4 deprivation in females. Although gonadal hormones may modify basal plasma 1,25-(OH)2-D levels, they are not required for the augmentation of plasma 1,25-(OH)2-D levels in response to PO4 deprivation.
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  • 36
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    Calcified tissue international 33 (1981), S. 575-581 
    ISSN: 1432-0827
    Keywords: Osteoporosis ; Vitamin D ; Bone mineral ; Estrogen ; Aging ; Thiazide ; Fluoride ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Bone mineral content (BMC) was measured by125I photon absorptiometry every 3 months in 264 normal females (45–54 years) over a 2-year period together with serum samples for calcium, phosphate, magnesium, creatinine, alkaline phosphatases, potassium, and protein. A 48-h urinary calcium and creatinine measurement was obtained. The subjects were divided into 7 treatment groups and 3 placebo groups. Five of the treatments (thiazide, vitamin D3, fluoride + vitamin D3, fluoride, and 1αD3) were ineffective at the doses used; the annual loss of compact bone was 1.5–2.2% (-X=1.8%), similar to the loss seen with placebos. Estrogen and estrogen + thiazide, in contrast, produced a 1.34% annual increase of BMC. The subjects were divided into groups with low, medium, and high initial BMC. Also, individual regressions for bone change were calculated and the subjects were divided into groups of responders, maintainers, and losers (annual change of 〉0%, 0 to −1%, and 〉−1%, respectively). The initial BMC status did not consistently affect bone or biochemical responses to the therapeutic agents. Estrogen was effective even in subjects with high BMC, whereas the other agents did not inhibit bone loss even in subjects with low initial BMC. Virtually all subjects responded to estrogen positively; in contrast we could not identify a subset of “responders” with any of the other treatments. Time since menopause appeared to influence the bone changes, although it was not a significant effect given the sample size. Bone loss in groups not treated with estrogens was 2%/year at 20 months after menopause with a decline to 1.3%/year at 45 months post-menopause. There was no apparent decline in the bone response to estrogen during the first 4 years after menopause, and in fact bone response tended to increase with time.
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  • 37
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    Calcified tissue international 33 (1981), S. 485-488 
    ISSN: 1432-0827
    Keywords: 1,25-(OH)2-D ; Hypophysectomy ; Calcium ; Phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The mechanism by which dietary phosphate deprivation elevates plasma 1,25-(OH)2-D levels is not known. To evaluate the role of the pituitary in regulating plasma 1,25-(OH)2-D concentrations, the responses of plasma 1,25-(OH)2-D to dietary phosphate deprivation and, separately, to dietary calcium deprivation were evaluated in intact and hypophysectomized male rats. Among intact and hypophysectomized rats eating normal diets, plasma 1,25-(OH)2-D levels averaged 228±76 and 148±62 pmol/1, respectively (P〈0.01). During dietary phosphate deprivation, plasma 1,25-(OH)2-D levels rose to 1160±260 in intact rats and fell to 90±26 pmol/l in hypophysectomized rats (P〈0.001). By contrast, during dietary calcium deprivation, plasma 1,25-(OH)2-D levels rose in both intact and hypophysectomized animals to 856±107 and 742±279 pmol/l, respectively (NS). In response to dietary phosphate deprivation, serum calcium concentrations rose as 1,25-(OH)2-D concentrations rose in intact rats but remained at control levels in hypophysectomized rats. These results support the hypothesis that a pituitary hormone acting either directly or indirectly on the kidney mediates the increase in plasma 1,25-(OH)2-D during dietary phosphate deprivation. The hypercalcemia that occurs in rats during dietary phosphate deprivation appears to depend on the elevation of plasma 1,25-(OH)2-D.
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  • 38
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    Calcified tissue international 30 (1980), S. 27-34 
    ISSN: 1432-0827
    Keywords: Ultrastructure ; Calcium ; Cartilage ; Vesicles
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    Topics: Biology , Medicine , Physics
    Notes: Summary The potassium pyroantimonate technique was utilized for the selective subcellular localization of calcium in the mandibular condylar cartilage of 1-day-old rats. Electron dense calcium pyroantimonate precipitates were localized principally in mitochondria and at the cell membrane of the chondrocytes. In addition, small intracellular vesicles 0.1–0.2µm in diameter were observed in proximity to the cell membrane of chondrocytes of the mid-hypertrophic zone. The results suggest that these vesicles were being extruded from the cell into the extracellular matrix. Energy-dispersive analysis by X-rays confirmed that calcium is the principal cation of the electron-dense precipitates.
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  • 39
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    Calcified tissue international 34 (1982), S. 43-48 
    ISSN: 1432-0827
    Keywords: Calcium ; Phosphate ; Phosphatidylserine ; Transport ; Mineralization
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    Notes: Summary Experiments were performed to study the effect of inorganic phosphate (Pi) on phosphatidylserine-mediated Ca2+ transport utilizing two- and three-compartment lipid-aqueous phase model systems. When the three-compartment model was used, the rate of Ca2+ transport from an aqueous donor compartment to an aqueous receiver compartment, separated by a nonaqueous phospholipid phase, was determined. This experiment showed that the rate of Ca2+ transport was proportional to the phosphatidylserine concentration and the pH. Pi modulated the rate of Ca2+ transport; even when the Pi concentration of the donor aqueous phase was low, there was a marked enhancement of transport. To determine whether the Pi-mediated rise in the Ca2+ transport rate was due to an increase in the uptake of Ca2+ into the lipid phase, or to an increase in the ability of the lipid phase to release Ca2+, a two-compartment model was used. It was found that the ability of the phosphatidylserine phase to take up Ca2+ increased as the Pi concentration of the aqueous donor phase was raised. With the increase in Ca2+ uptake there was a concomitant elevation in the rate of Ca2+ transport into an aqueous receiver phase. However, Pi did not stimulate Ca2+ release from the phosphatide. Thus it was concluded that Pi enhanced the interaction between Ca2+ and phosphatidylserine, possibly by forming a Ca-phospholipid-Pi complex. Once this interaction had taken place, Ca2+ release into the aqueous receiver compartment was independent of the Pi concentration.
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  • 40
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    Calcified tissue international 36 (1984), S. 77-82 
    ISSN: 1432-0827
    Keywords: Osteogenesis ; Diffusion chambers ; Alkaline phosphatase ; Calcium ; Phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The alkaline phosphatase activity and the calcium and phosphorus content of osteogenic tissue formedin vivo following the implantation of diffusion chambers loaded with rabbit bone marrow cells is reported. (In this study the term osteogenic includes osteoblastic and chondroblastic.) Chambers examined 14–70 days after implantation revealed progressive accumulation of mineral. Alkaline phosphatase activity increased until day 30 and declined thereafter. The osteogenic potential of the marrow cells decreased with increasing weight (age) of the cell donor rabbit when measured either as the percentage of chambers containing osteogenic tissue or as the amount of calcium, phosphorus, or alkaline phosphatase activity within the chambers. The results confirm that measurements of these parameters in tissue formed by cells incubated in diffusion chambersin vivo may be used as a method for assay of osteogenesis.
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  • 41
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    Calcified tissue international 36 (1984), S. 269-273 
    ISSN: 1432-0827
    Keywords: Bone loss (osteopenia) ; Calcium ; Corticosteroids (glucocorticosteroids) ; Fluoride ; Vitamin D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary To evaluate the effect of prednisone and triple treatment (sodium fluoride, calcium, and vitamin D) on trabecular and cortical bone serial bone mineral content (BMC) measurements were made at a metaphyseal (BMCD) and diaphyseal (BMCP) site on the forearm on 31 consecutive and previously bone-healthy patients scheduled for at least 24 weeks high-dose prednisone treatment. The patients were randomized into two further treatment groups: group I (n=16) received prednisone plus triple treatment and group II (n=15) received only prednisone. The two groups were similar with regard to age, sex, prednisone dose, and initial BMC. During 24 weeks treatment, BMCD (partially representing trabecular bone) and BMCP (mainly representing cortical bone) fell significantly and similarly, demonstrating that there is no preventive effect on bone mineral loss on the triple regimen. The BMC fall after 12 weeks was significantly more pronounced for metaphyseal (partially trabecular) than for diaphyseal (cortical) bone, whereas the values did not differ significantly after 24 weeks; this indicates a greater sensitivity to the hormone treatment of trabecular bone. In the entire group, the fall in BMC correlated positively with individual prednisone dose, significant at the diaphyseal site (r=0.39,P〈0.05), but not at the metaphyseal site (r=0.31, P=0.08). It is concluded that corticosteroid-induced osteopenia is a diffuse bone disease which affects trabecular as well as cortical bone, suggesting that BMC measured on the forearm reflects changes in bone mineral at other locations.
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  • 42
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    Calcified tissue international 36 (1984), S. 392-400 
    ISSN: 1432-0827
    Keywords: Vitamin D ; Chick embryo ; Bone ; Calcium ; Phosphate
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    Topics: Biology , Medicine , Physics
    Notes: Summary Chick embryos were injected in the yolk sac at various ages with various doses of different vitamin D3 metabolites. Serum concentrations of total calcium and inorganic phosphate were determined 24 h after the injection and histological and electron microscopic studies of the tibiae were conducted 3–6 days after. Confirming previous results, the injection of 1,25(OH)2D3 was found to produce significant hypercalcemia and hypophosphatemia. The dose required to produce these effects decreased with age: 100 ng on the 9th day, 50 ng on the 11th, and 10 ng on the 15th. This finding is interpreted as resulting from the fact that the specialized cells in the chorionic epithelium which are considered to be involved in mineral resorption from the shell differentiate between the 11th and 13th days. Although no bone changes were observed in embryos injected before the 11th day, a rim of unmineralized trabeculae (osteoid) was observed at the periphery of the cortex of the tibial diaphysis in the embryos which had been injected after that age. Thus, in embryos injected on the 11th day with 100 ng 1,25(OH)2D3, the trabeculae formed between the 11th and 14th day remained unmineralized until the 15th or 16th day at which time they completed their mineralization. In the embryos injected on the 14th day, the alterations were more severe and could be produced with doses 10 times smaller than those required when the injections were made on the 11th day. At all ages, the doses that produced an osteoid rim also induced hypercalcemia and hypophosphatemia. The electron microscopical study of the osteoid trabeculae showed that osteoblasts and osteocytes had normal cytological characteristics and that the bone matrix did not present changes other than the reduction in mineral deposition. While the above findings do not exclude a direct action of 1,25(OH)2D3 on bone cells as the mechanism of osteoid formation, they do underline the importance of the humoral changes at least as partial determinants of this phenomenon. The activities of various vitamin D metabolites were compared using as parameter the threshold-dose required to produce a rim of unmineralized trabeculae in the tibia of 14–15 days embryos (T-D). The most active metabolite appeared to be 1,25(OH)2D3 (T-D: 10 ng); it was followed by 1,24,25(OH)3D3 (T-D: 100 ng) and 1,25,26(OH)3D3 (T-D: 100 ng). Vitamin D3 itself (T-D: 100 µg), 25(OH)D3 (T-D: 2.5µg) and 24,25(OH)2D3 (T-D: 5 µg) produced similar responses but only when administered in much larger doses.
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  • 43
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    Calcified tissue international 36 (1984), S. 702-710 
    ISSN: 1432-0827
    Keywords: Corticosteroids ; Cartilage ; Organ culture ; Calcium ; Matrix vesicles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The present study examined the effects of various corticosteroid and noncorticosteroid hormones upon the ultrastructure of chondroprogenitor cells and chondroblasts in an organ-culture system of late fetal condylar cartilage. Corticosteroids, (triamcinolone acetonide, dexamethasone, corticosterone) at concentrations of 10−6–10−8M stimulated markedly a precocious formation of matrix vesicles by chondroblasts. This stimulation was accompanied by a significant accretion of calcium complexes intra- and extracellularly in both the chondroprogenitor cell population and chondroblastsin vitro, as well as in the newly induced matrix vesicles. Nonglucocorticoid steroids (progesterone, estradiol, testosterone, cortexolone) did not evoke similar effects. Progesterone and testosterone, however, seemed to adversely affect the ultrastructure of the cartilage cells, whereas estradiol appeared to have a favorable effect on the morphology of cultured condylar cartilage.
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  • 44
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    Calcified tissue international 34 (1982), S. 121-124 
    ISSN: 1432-0827
    Keywords: Bone ; Calcium ; Metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Bone Gla protein (BGP) was measured in the plasma by radioimmunoassay (RIA) during treatment of 59 patients with bone diseases including Paget's disease (N=9), primary hyperparathyroidism (N=25), chronic renal failure (N=20), and cancer involving bone (N=5). Plasma BGP was increased above normal in all patients. BGP decreased in the patients with Paget's disease following the acute and chronic administration of salmon calcitonin. Plasma BGP was higher in women then in men with primary hyperparathyroidism. Following parathyroidectomy, BGP decreased in both sexes but the decrease was significant in women only. Plasma BGP was increased in patients with renal osteodystrophy and did not change after hemodialysis. In the patients with bone cancer, plasma BGP decreased during treatment of the attendant hypercalcemia with salmon calcitonin. Although plasma BGP and serum alkaline phosphatase (AP) levels were generally correlated in these studies, there were examples of dissociation between the two. The measurement of plasma BGP appears to provide a specific index of bone metabolism that may in some circumstances be more sensitive than serum alkaline phosphatase measurement. However, further studies are necessary to establish the clinical value of plasma BGP measurement by RIA in the management of patients with bone diseases.
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  • 45
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    Calcified tissue international 35 (1983), S. 107-110 
    ISSN: 1432-0827
    Keywords: Calcium ; Glucocorticoid ; Vitamin D ; Osteoporosis ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Eighty-eight adult male Sprague-Dawley rats were given a diet with either (a) 0.5% Ca and 0.6% P or (b) 0.01% Ca and 0.6% P. Osteopenia was created by adding prednisolone to the diet. The prophylactic effect of oral 1,25(OH)2D3 on the osteopenia was studied. It was found that prednisolone osteopenia in the rat was associated with defective Ca absorption. By giving an oral dose of 1,25(OH)2D3, it was possible to maintain normal Ca absorption during prednisolone treatment and to prevent the bone loss. No significant hypercalcemia or any kidney calcifications were seen. These results are in contrast to earlier findings, in which subcutaneous administration of 1,25(OH)2D3 failed to prevent prednisolone osteopenia because of its tendency to increase bone resorption.
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  • 46
    ISSN: 1432-0827
    Keywords: 31P NMR spectroscopy ; Phosphoprotein ; Dentin ; Calcium ; Inorganic orthophosphate ; Bovine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The single phosphoprotein of fetal calf dentin, having a molecular weight of approximately 94,000 and a phosphorus content of 8% (w/w), was examined by31P NMR spectroscopy. The single resonance at 3.7 ppm at pH 10 and its chemical shift during acid titration established the phosphomonoester nature of the organic phosphorus moiety. During titration of the phosphoprotein with CaCl2 in the presence of inorganic orthophosphate ions, line broadening for the orthophosphate resonance was both phosphoprotein- and calcium-dependent, indicating ternary complex formation. The data indicate that the phosphoprotein of fetal calf dentin binds both calcium and inorganic orthophosphate ions and therefore has the requisite physical chemical properties necessary for it to facilitate the heterogeneous nucleation of a Ca-PO4 solid phase from solution during tissue mineralization.
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  • 47
    ISSN: 1432-2048
    Keywords: Calcium ; Calmodulin ; Malus (protein kinase) ; Protein kinase
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    Topics: Biology
    Notes: Abstract Crude Ca2+-activated protein kinase from membranes of apple (Malus domestica L. Borkh., Cox's Orange Pippin) fruit can be partially purified to yield a Ca2+-dependent protein kinase whose activity is apparently not regulated by calmodulin. The autophosphorylating catalytic subunit of this protein kinase shows a Ca2+-dependent mobility shift of approx. 10 kilodaltons (kDa) on sodium dodecyl sulphate-polyacrylamide gel electrophoresis; in the absence of added Ca2+ or ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) its apparent molecular mass is approx. 50 kDa. The Ca2+-dependent protein kinase is inhibited by the calmodulin antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide and trifluoperazine with IC50 values of approx. 45 μM and 15 μM, respectively. These similarities between the protein kinase and calmodulin indicate that the kinase may be a calmodulin-like protein.
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  • 48
    ISSN: 1432-2048
    Keywords: Calcium ; Cation exchange ; Lycopersicon esculentum ; Rhythm ; diurnal Transport (calcium) ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Tomato (Lycopersicon esculentum Mill. cv. Moneymaker) and maize (Zea mays L. cv. spec.) plants were supplied with 45Ca-labeled nutrient solutions for a period of 8 or 16 h in the dark, in the light, or in a light-dark régime. Plant parts were analyzed for 45Ca content. The partitioning of 45Ca between mature leaves and meristems was shown to be affected by the presence of light. The transport of 45Ca to meristems was higher in a dark period than in a comparable light period. Experiments with excised tomato shoots yielded similar distribution patterns of 45Ca over leaves and meristems, thus excluding root pressure as the main driving force for the enhanced import of 45Ca into the meristems in the dark. Results are discussed in terms of cation-exchange transport and competition between the various calcium sinks.
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  • 49
    ISSN: 1432-2048
    Keywords: Calcium ; Fluorescein isothiocyanate ; Lanthanum ; Pollen tube ; Ruthenium red ; Tip extension ; Tradescantia ; Trifluoperazine ; Vesicle (transport, fusion)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of ruthenium red, lanthanum, fluorescein isothiocyanate and trifluoperazine, all antagonists of Ca2+ function in cells, have been studied in growing pollen tubes of Tradescantia virginiana. All four drugs inhibit pollen-tube growth but bring about different ultrastructural changes at the growing tips and within the cytoplasm. The results strongly support the hypothesis that Ca2+ plays a vital role in the mechanism of pollen-tube tip growth. The effect of ruthenium red provides evidence that sequestration of Ca2+ by mitochondria critically adjusts the concentration of these ions at tube tips. Fluorescein isothiocyanate appears to be a potent inhibitor of vesicle fusion at the plasma membrane, with vesicles accumulating in the tip at rates equivalent to those determined previously for their production. Both vesicle fusion and tip extension are regulated by Ca2+ but appear to be independently controlled processes.
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  • 50
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    Planta 158 (1983), S. 320-328 
    ISSN: 1432-2048
    Keywords: Calcium ; Egeria ; Fluorescent probe ; Ions, group II ; Symplast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The hydrophyllic dyes fluorescein glutamic acid, fluorescein glutamylglutamic acid (F(Glu)2), fluorescein hexaglycine, fluorescein leucyldiglutamyl-leucine and 6-carboxyfluorescein are unable to pass the plasmalemma in leaves of E. densa. However, when injected into single cells the dye conjugates of molecular weight 665 dalton or less move freely from cell-to-cell. This intercellular movement presumably occurs via the plant symplast. Movement of F(Glu)2 from the injected cell occurs with greatly reduced frequency when Ca2+, Mg2+ or Sr2+ are injected into the cell immediately prior to the dye. The fraction of dye injections leading to movement declines with increasing group II ion concentration in the electrode tip, up to 10 mM. Sodium and K ions do not affect dye movement. When dye injection is delayed 30 min after Ca2+ injection, dye movement is no longer inhibited. Thus the cells recover from the Ca2+ injection, indicating that the ion does not cause major cell damage. Recovery from Mg2+ injection is not complete within 60 min. Treatment of leaves with chemicals expected to raise the concentration of free intracellular group II ions, notably the mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenyl hydrazone, the inhibitor of mitochondrial Ca2+ uptake trifluralin, or the ionophore A23187 also inhibits dye movement, while the calmodulin inhibitor trifluoperazine does not. Cytoplasmic streaming is inhibited by Ca2+ or Mg2+ injection and by the metabolic inhibitors. However when streaming is stopped by cytochalasin B, dye movement is not inhibited. Hence steaming is not necessary for dye movement. Thus the cytoplasmic concentration of free group II ions may directly regulate the permeability of the plant symplast.
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  • 51
    ISSN: 1432-2048
    Keywords: Bryophyta ; Bud formation (moss) ; Calcium ; Chlorotetracycline ; Cytokinin ; Funaria
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    Topics: Biology
    Notes: Abstract We have investigated the changes in membrane-associated calcium that occur during cytokinin induced bud formation in Funaria hygrometrica Hedw. using the fluorescent Ca2+-chelate probe chlorotetracycline (CTC). In the target caulonema cells a localization of CTC fluorescent material becomes evident at the presumptive bud site 12 h after cytokinin treatment. By the time of the initial asymmetric division this region is four times as fluorescent as the entire caulonema cell. Bright CTC fluorescence remains localized in the dividing cells of the bud. To relate the changes in CTC fluorescence to changes in Ca2+ as opposed to membrane-density changes we employed the general membrane marker N-phenyl-1-naphthylamine (NPN). NPN fluorescence increases only 1.5 times in the initial bud cell. We conclude that the relative amount of Ca2+ per quantity of membrane increases in this localized area and is maintained throughout bud formation. We suggest that these increases in membrane-associated Ca2+ indicate a localized rise in intracellular free Ca2+ concentration brought about by cytokinin action.
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  • 52
    ISSN: 1432-2048
    Keywords: Calcium ; Lilium ; Membrane distribution ; Pollen germination ; Proton microprobe
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    Topics: Biology
    Notes: Abstract Chlorotetracyclin (10-4M) has been used to observe the distribution of membrane-associated calcium during pollen germination of Lilium longiflorum. For comparison, the general membrane distribution has been determined with 4·10-5 M fluorescamine. The pollen grains show a calcium gradient with either weak or strong chlorotetracycline-fluorescence intensity, but always increasing toward the germination colpus. This gradient intensifies during germination, reaching a maximum before the pollen tube emerges. The typical tip-to-base calcium gradient of the tube does not change during growth. Independent of the developmental stage, the pollen grains show a flat fluorescamine-fluorescence gradient with the highest intensity in one half of the grain. Pollen tubes reveal a tip-to-base membrane gradient, independent of their length. As an additional marker for membrane distribution, the distribution of phosphorus, measured by proton-induced X-ray emission in chemically fixed tubes, has been used. A tip-to-base phosphorus gradient, distinct from the calcium gradient measured with the same method, was detected.
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  • 53
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    Planta 152 (1981), S. 450-456 
    ISSN: 1432-2048
    Keywords: Calcium ; Cell elongation ; Gibberellin ; Lactuca ; pH and growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between calcium ions and gibberellic acid (GA3)-induced growth in the excised hypocotyl of lettuce (Lactuca sativa L.) was investigated. The short-term kinetics of growth responses were measured using a linear displacement transducer. Test solutions were added either as drops to the filter paper on which the hypocotyl stood (“non-flow-past”) or by switching solution flowing past the base of hypocotyl (“flow-past”), resulting in differences in growth behavior. Drops of CaCl2 added at a high concentration (10 mM) inhibited growth within a few minutes. This inhibition was reversed by ethylenediaminetetraacetic acid (EDTA). Drops of EDTA or ethyleneglycol-bis(2-aminoethylether)-tetraacetic acid caused a rapid increase in growth rate. Growth induced by EDTA was not further promoted by GA3. A continuous H2O flow resulted in growth rates comparable to those in response to GA3. Addition of CaCl2 to the flow-past medium inhibited growth and this inhibition was reversed by a decrease in CaCl2 concentration. The growth rate was found to be a function of CaCl2 concentration. When a constant CaCl2 concentration was maintained by the flow-past medium, a shift in pH from 5.5 to 4.25 had no obvious effect on hypocotyl elongation. Gibberellic acid was found to reverse the inhibitory effect of CaCl2, causing an increase in growth rate similar to that found previously when GA3 was added to hypocotyls grown in H2O under non-flow-past conditions. We propose that gibberellin controls extension growth in lettuce hypocotyl sections by regulating the uptake of Ca2+ by the hypocotyl cells.
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  • 54
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    Sexual plant reproduction 2 (1989), S. 11-14 
    ISSN: 1432-2145
    Keywords: Boric acid ; Pollen ; Petunia hybrida ; Temperature discontinuities ; Protein release ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Energy-driven protein secretion from Petunia hybrida pollen in 10% sucrose solution shaking culture does not change markedly with temperature, except over a narrow (6° C) temperature range with a midpoint at 17° C. Over this narrow temperature range, there is a very rapid increase from a low secretion plateau at low temperatures to a plateau of higher secretion at higher temperatures. Addition of calcium ions decreases the overall amount secreted, but does not change the critical temperature where the rapid rise in secretion is observed. Boric acid, when added to the culture, also decreases the overall amount released, but in a different way to calcium. While there is a sharp discontinuity at 17° C as before, the increase in protein release at this temperature is smaller than before. In addition, after a plateau at temperatures higher than 20° C, there is a second sharp increase in secreted protein over another narrow temperature range with a midpoint of 28° C, followed by another plateau at higher temperatures. The effects of calcium and boric acid are additive. The sharp discontinuities in protein release are interpreted in terms of lipid thermotropism in membranes and a boron involvement in the movement of proteins into the extending pollen tube membranes from secretory vesicles.
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  • 55
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    Sexual plant reproduction 2 (1989), S. 277-280 
    ISSN: 1432-2145
    Keywords: Brassica oleracea ; Pollen germination ; In vitro assay ; Calcium ; Self-incompatibility ; S locus-specific glycoproteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Eluates of stigmas of Brassica oleracea that were known to contain S locus-specific glycoproteins (SLSG) discriminated between self and cross pollen in vitro in three different media. Discrimination was equally evident in experiments that were the in vitro equivalents of reciprocal pollinations. In a TAPS-buffered medium, self eluates depressed pollen germination in a dose-dependent manner. TAPS medium allowed a bioassay of the effects of SLSG in eluates because it optimized germination in a way that eliminated the complicating features of the stimulatory substances in the eluates. Stigma eluates affected percentage pollen germination and optimum calcium concentrations in vitro whether or not SLSG were present in the eluates, but differently in different media, and depending on whether the eluates were cross or self with respect to the pollen tested. Thus, the effect of stigma eluates on the in vitro germination of pollen in Brassica depends on the balance of stimulatory versus inhibitory substances in the eluates.
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  • 56
    ISSN: 1432-1009
    Keywords: Acid precipitation ; Biomass nutrients ; Calcium ; Clearcutting ; Magnesium ; Nitrogen ; Phosphorus ; Potassium ; Soil leaching ; Soil nutrients ; Timber harvest ; Weathering ; Whole-tree harvest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Both harvest removal and leaching losses can deplete nutrient capital in forests, but their combined long-term effects have not been assessed previously. We estimated changes in total soil and biomass N, Ca, K, Mg, and P over 120 years from published data for a spruce-fir site in Maine, two northern hardwood sites in New Hampshire, central hardwood sites in Connecticut and Tennessee, and a loblolly pine site in Tennessee. For N, atmospheric inputs counterbalance the outputs, and there is little long-term change on most sites. For K, Mg, and P, the total pool may decrease by 2%–10% in 120 years depending on site and harvest intensity. For Ca, net leaching loss is 4–16 kg/ha/yr in mature forests, and whole-tree harvest removes 200–1100 kg/ha. Such leaching loss and harvest removal could reduce total soil and biomass Ca by 20%–60% in only 120 years. We estimated unmeasured Ca inputs from rock breakdown, root-zone deepening, and dry deposition; these should not be expected to make up the Ca deficit. Acid precipitation may be the cause of current high leaching of Ca. Although Ca deficiency does not generally occur now in acid forest soils, it seems likely if anthropogenic leaching and intensive harvest removal continue.
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  • 57
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    European biophysics journal 9 (1982), S. 131-136 
    ISSN: 1432-1017
    Keywords: Chemotaxis ; Calcium ; Oscillation ; Dictyostelium ; Ionophore
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Migration of differentiated cells to a capillary containing cyclic AMP was enhanced in the presence of 1 mM CaCl2 and was virtually absent in the presence of 1 mM EGTA. Furthermore, the cells contracted and extended pseudopods to a capillary filled with the calcium ionophore A 23187. At short distances, migration to the tip of the capillary was observed. The ionophore also induced transient decreases of the optical density of suspended cells indicating changes of cell shape. These findings support the hypothesis that cyclic AMP-binding to cell surface receptors causes a local influx of calcium ions. These in turn lead to an increase of the cytosolic calcium concentration and subsequently to an activation of cell migration. Perturbing pulses of the ionophore induced permanent phase shifts of free-running light scattering oscillations. This result indicates that cytosolic calcium is an intrinsic component of the oscillatory system.
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  • 58
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    Archives of microbiology 149 (1988), S. 565-571 
    ISSN: 1432-072X
    Keywords: Phytophthora ; Zoospores ; Calcium ; Encystment ; Differentiation ; Pectin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A method has been developed for the preparation of zoospores from Phytophthora palmivora which allows the ionic composition of the suspension medium to be closely controlled. Sub-micromolar concentrations of calcium ions have been shown to play a key role in maintaining the zoospore state and in the transition to the cyst stage. Restriction of free Ca2+ to between 0.2 and 1 μM resulted in zoospores which could be maintained for several hours before they finally encysted and germinated. When exposed to citrus-pectin, or 3 mM SrCl2, or to vigorous shaking, these zoospores underwent rapid synchronous encystment. At free Ca2+ concentrations below 0.1 μM, zoospores lysed slowly. If exposed to inducers of encystment before lysis had occurred, the zoospores failed to respond to pectin or to vigorous shaking. However, they did differentiate in response to SrCl2 addition. Provided the free Ca2+ was maintained between 0.02 and 0.2 μM, zoospores survived gentle centrifugation, a procedure which previously had resulted in encystment.
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  • 59
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    Archives of microbiology 149 (1987), S. 24-29 
    ISSN: 1432-072X
    Keywords: Frankia ; Nitrogen fixation ; Calcium ; Vesicle development
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    Topics: Biology
    Notes: Abstract A calcium requirement was shown for both vesicle development and nitrogenase activity by Frankia strains EAN1pec and CpI1. Washing cells with EGTA or EDTA inhibited both vesicle development and nitrogenase activity. The inhibition of both was reversed by the addition of calcium. A variety of agents known to affect calcium-dependent biological processes, such as a Ca-ATPase inhibitor, Ca-channel blockers, Ca-ionophores, calmodulin antagonists and the local anaesthetics, tetracaine and dibucaine, inhibited nitrogenase activity. Respiratory studies showed that a CN-insensitive respiration process occurred only under nitrogen derepressing conditions. Respiration by NH4Cl-grown cells was completely inhibited by KCN while N2-grown cells were inhibited by only 70%. Removal of calcium ions by EGTA or by the addition of dibucaine or tetracaine blocked the CN-insensitive respiration. This CN-insensitive respiration may be involved in protecting nitrogenase inside the vesicles from oxygen.
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  • 60
    ISSN: 1432-072X
    Keywords: Phototaxis ; Motility ; Flagellate ; Chlamydomonas ; Sodium azide ; Calcium ; A 23 187
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A fully automated and computerized method for simultaneous measurements of motility and phototaxis of unicellular flagellates is described. Both systems are directly coupled with a homocontinuous culture. The motility measuring apparatus is equipped with a video camera and recorder for simultaneous single cell behaviour studies. First results of studies on the effects of the phototaxis inhibitor sodium azide and the Ca2+ conducting ionophore A23 187 on motility and phototaxis of Chlamydomonas are reported and correlated with video observations. These results demonstrate that the described systems give informations of whether phototaxis or motility or both are inhibited by chemicals.
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  • 61
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    Archives of microbiology 144 (1986), S. 393-397 
    ISSN: 1432-072X
    Keywords: Chlamydomonas reinhardtii ; Phototaxis ; Motility ; Flagellates ; Flagellar movement ; Calcium ; Calcium channel blockers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of the four calcium channel blockers flunarizine, verapamil, diltiazem and nimodipine on motility and phototaxis of Chlamydomonas reinhardtio have been tested with a fully automated and computerized population system. Flunarizine inhibits motility transiently by causing the detachement of the flagella which, however, are regenerated during some hours. Phototaxis is inhibited to the same extent, but this is simply the result of the decreased motility and, hence, a non-specific effect. Verapamil causes also a detachement of the flagella with following regeneration, but in addition motility and phototaxis are inhibited by this drug to different extents, indicating the involvement of calcium channels in both processes. Diltiazem and nimodipine inhibit phototaxis without impairing motility, indicating that both processes are regulated in different ways. If diltiazem and nimodipine are applied simultaneously, no additive inhibitory effect can be observed. However, the combination of both blockers with verapamil causes and additive inhibitory effect as if verapamil is applied alone. By increasing the external calcium concentration from 10-4 M to 10-3 M the optimum of positive phototaxis is shifted to higher fluence rates. This shifting occurs also in the presence of channel blockers, but the strength of the positive reaction is influenced. These results point to the involvement of calcium channels in both phototaxis and motility, but simultaneously demonstrate the different sensitivity of the two processes to these drugs.
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  • 62
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    Archives of microbiology 138 (1984), S. 140-152 
    ISSN: 1432-072X
    Keywords: Caulobacter ; Prostheca development ; Stalk function ; Calcium ; Phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Calcium was found to stimulate stalk development in Caulobacter crescentus and to relieve the inhibition of development long known to be caused by phosphate. This suggested that phosphate inhibition could be attributed to its interaction with Ca2+, thereby depriving the cells of a factor that promoted development. Calcium was also found to promote phosphate acquisition by the cells, observed as acceleration of growth at extremes of phosphate concentration, as promotion of carbon-source utilization rather than storage, and as support for phosphate-dependent resistance to arsenate inhibition of growth. Cytological studies of dividing cells revealed that stalked siblings had greater access to exogenous phosphate for use in growth or for storage as polyphosphate, and that access of non-stalked sibling to phosphate was dependent on the length of the stalk of the dividing cell. It was concluded that the physiologic role of the stalk is enhancement of phosphate acquisition. The stimulatory role of calcium in this process was attributed to its support of stalk development and to its stabilization of internal membrane/cell envelope association within the cell-stalk juncture.
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  • 63
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    Archives of microbiology 139 (1984), S. 102-104 
    ISSN: 1432-072X
    Keywords: Fungus ; Zoospore ; Blastocladiella ; Allomyces ; Gamma ; Particle ; Phosphate ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The elemental composition of gamma particles in zoospores ofAllomyces macrogynus andBlastocladiella emersonii was determined by use of energy dispersive X-ray analysis of glutaraldehyde fixed, thin section zoospores. Isolated preparations of gamma particles were also examined. Gamma particles contained no detectable elements. Similar sized, globular, electron dense cytoplasmic inclusions contained phosphorus and calcium. We suggest that previous studies assigning calcium and phosphorus to gamma particles may have been based on confusion of these two types of cytoplasmic inclusions.
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  • 64
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    Archives of microbiology 149 (1988), S. 451-458 
    ISSN: 1432-072X
    Keywords: Chlamydomonas reinhardtii ; Phototaxis ; Galvanotaxis ; Calcium ; Calcium channels ; Calcium channel blockers ; Radioligand binding ; Polymer twophase system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Specific binding of the calcium antagonist [3H]verapamil to a microsomal fraction, a presumptive plasma membrane fraction and an intracellular membrane fraction of the phototactic unicellular green alga Chlamydomonas reinhardtii has been demonstrated. The specific activity of the plasma membrane marker enzyme K+-stimulated, Mg2+-dependent ATPase was severalfold higher in the upper (polyethylene glycol-rich) than in the lower (dextran-rich) phase, and the reverse was established for the marker enzymes of intracellular membranes such as cytochrome c oxidase for mitochondria and antimycin Aresistant NADPH-cytochrome c reductase for endoplasmic reticulum. Chlorophyll as a marker for thylakoid fragments was exclusively found in the lower phase. In the microsomal fraction two specific binding sites of [3H]verapamil were found at 22°C, one with higher and a second with lower affinity to [3H]verapamil. Separation of plasma membranes from intracellular membranes revealed that the “highaffinity” binding site is attributed to the plasma membrane fraction whereas the “low-affinity” binding site can be attributed to the intracellular membrane fraction. Specific binding to both separated membrane fractions is saturable and reversible. [3H]Verapamil binding to plasma membranes was not inhibited by the calcium channel blockers diltiazem and nifedipine. However, in the intracellular membrane fraction [3H]verapamil could be displaced by diltiazem but not by nifedipine. Increasing concentrations of calcium chloride inhibited [3H]verapamil binding in both fractions.
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  • 65
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    Archives of microbiology 150 (1988), S. 109-112 
    ISSN: 1432-072X
    Keywords: Calcium ; Dunaliella tertiolecta ; Enzyme kinetics ; Glycerol ; Glycerol-3-phosphatase ; Metabolic regulation ; Osmoacclimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Glycerol-3-phosphatase (EC 3.1.3.2.1) was studied by following the release of radioactive glycerol from L-(U-14C)glycerol-3-phosphate in Dunaliella tertiolecta enzyme extracts. The reaction showed a neutral pH optimum and had an absolute requirement for Mg2+. The substrate saturation curve was hyperbolic with an apparent K m value for glycerol-3-phosphate of 0.7 mM in the absence of phosphate. Inorganic orthophosphate was a competitive inhibitor of the enzyme with an estimated K j of 0.1 mM. The glycerol-3-phosphatase reaction was blocked nearly completely by millimolar Ca2+ concentrations. Ca2+ inhibition did not depend on the presence of calmodulin in the reaction medium. The characteristics of glycerol-3-phosphatase are discussed in relation to the regulation of the cyclic glycerol metabolism in Dunaliella cells during periods of osmotic stress.
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  • 66
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    Archives of microbiology 151 (1989), S. 187-190 
    ISSN: 1432-072X
    Keywords: Calcium ; Calcium channel blocker ; Dinoflagellate ; Gyrodinium dorsum ; Motility ; Phytochrome ; Stop-response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of the calcium channel blockers, verapamil, diltiazem and lanthanum ions and the Ca2+ dependency on motility as well as the photophobic response (stop-response) of Gyrodinium dorsum were studied. At Ca2+ concentrations below 10-3 M, motility was inhibited. La3+ inhibits the stop-response, in contrast to verapamil and diltiazem. The only calcium channel blocker that increased the amount of non-motile cells was verapamil. The results indicate that motility are Ca2+ dependent and that the stop-responses of G. dorsum could be affected by extracellular Ca2+. Effects of the photosythesis inhibitor (DCMU) on the stop-response was also determined. With background light of different wavelength (614, 658 and 686 nm) the stop-response increased. DCMU inhibited this effect of background light. Negative results with the monoclonal antibody Pea-25 directed to phytochrome and the results with DCMU, indicate that the stop-response of G. dorsum is coupled to photosynthesis rather than to a phytochrome-like pigment. Oxygen evolution, but not cell movement, was completely inhibited by 10-6 M DCMU.
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  • 67
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    Archives of microbiology 152 (1989), S. 468-472 
    ISSN: 1432-072X
    Keywords: Calcium ; Phycomyces blakesleeanus ; Sporangiophore
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The in situ localization of Ca2+ in stage I sporangiophores of the fungus Phycomyces blakesleeanus was achieved with the potassium pyroantimonate technique. Precipitates of calcium-antimonate were present in mitochondria, vacuoles, endoplasmic reticulum and adjacent cytoplasm, “Golgi-like” bodies, and nuclei but not cell walls. Material treated with the calcium chelator EGTA lacked these precipitates. The preferential localization of Ca2+ in mitochondria, endoplasmic reticulum and vacuoles suggests that these organelles modulate the level of this cation in sporangiophores of P. blakesleeanus.
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  • 68
    ISSN: 1432-2048
    Keywords: Calcium ; Chloride ; Gravitropism ; Ion migration ; Mimosa ; Potassium ; Pulvinus ; Seismonasty
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When the leaves of Mimosa pudica are changed from their normal position in the gravitational field, they perform reversible compensatory movements by means of pulvini. These movements are not the result of growth processes but involve reversible turgor variations. These variation are concomitant with ion migrations within pulvini: during the gravitropic movement, K+ and Cl- shift towards the adaxial half of the motor organ whereas Ca2+ shifts towards the abaxial half. Compounds known to affect K+ transport, tetraethylammonium chloride and valinomycin, do not hinder the gravitropic movement but inhibit strongly the seismonastic reaction. The same general result is obtained with compounds affecting anion transport, disulfonic stilbenes and 9-anthracene carboxylic acid. Calcium chelators inhibit the gravitropic movement more efficiently than the seismonastic reaction and the calcium ionophore A 23 187 increases both movements. The data obtained with these various compounds indicate that ions do not have the same functional importance in the regulation of the two different pulvinar movements.
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  • 69
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    Planta 174 (1988), S. 495-499 
    ISSN: 1432-2048
    Keywords: Auxin, calcium and pH ; Calcium ; Cytosolic pH ; Membrane potential (double-barrelled micro-electrode) ; Zea (auxin, Ca2+, pH)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In epidermal cells of maize (Zea mays L.) coleoptiles, cytosolic pH (pHc), cytosolic free calcium, membrane potential and changes thereof were monitored continuously and simultaneously (pHc/,ψ m, Ca2+/ψ m) using double-barrelled ion-sensitive microelectrodes. In the resting cells the cytosolic pH was 7.3–7.5 and the concentration of free calcium was 119±24 nM. One-micromolar indole-3-acetic acid (IAA), added to the external medium at pH 6.0 triggered oscillations inψ m, pHc and free calcium with a period of 20 to 30 min. Acidification of the cytosolic pH increased the cytosolic free calcium. Theψ m oscillations are attributed to changes in activity of the H+-extrusion pump at the plasmalemma, triggered off by ΔpH and controlled by pH regulation (pH oscillation). The origin of the pHc and Ca2+ changes remains unclear, but is possibly caused by auxin-receptor-induced lipid breakdown and subsequent second-messenger formation. It is suggested that the observed cytosolic pH and Ca2+ changes are intrinsically interrelated, and it is concluded that this onset of regulatory processes through the phytohormone IAA is indicative of calcium and protons mediating early auxin action in maize coleoptiles. It is further concluded that the double-barrelled ion-sensitive microelectrode is an invaluable tool for investigating in-vivo hormone action in plant tissues.
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  • 70
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    Planta 160 (1984), S. 12-20 
    ISSN: 1432-2048
    Keywords: Calcium ; Calmodulin ; Germination (spore) ; Onoclea ; Phytochrome and Ca2+ ; Pteridophyta
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Phytochrome is confirmed to be the photoreceptor pigment in the germination response of Onoclea sensibilis L. by demonstrating red-far-red (R-FR) photoreversibility. External Ca2+ is required for this response with a threshold at a submicromolar concentration. Ethylene glycol-bis(β-amino-ethyl ether)-N,N,N′,N′-tetraacetic acid, La3+ and Co2+ reversibly inhibit germination. Lanthanum only inhibits germination when applied before or during irradiation, indicating that the external Ca2+ requirement is transient, although in the absence of Ca2+ the R-stimulated system remains maximally poised to accept the ion for over 4 h after irradiation. The ability to respond to Ca2+ 4.1 h after R-irradiation is not reversed by FR-irradiation, indicating that Ca2+ transport has been uncoupled from phytochrome. Barium and Sr2+, but not Mg2+ can substitute for Ca2+. Artificially increasing the concentration of intracellular free Ca2+ with the ionophore A 23187 stimulates germination in the dark. The Ca2+-calmodulin antagonists, trifluoperizine and chlorpromazine, reversibly inhibit germination. Calcium is required in phytochrome-mediated fern spore germination; it may be acting as a second messenger.
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  • 71
    ISSN: 1432-2048
    Keywords: Calcium ; Calmodulin ; Pisum (protein kinase) ; Plasma membrane ; Protein kinase
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    Notes: Abstract Membranes isolated from pea buds contain protein-kinase activity which is greatly activated by low concentrations of calcium ions. This paper describes a simple purification of this enzyme with a novel means of detecting enzyme activity by Western blotting. The purified enzyme appears to autophosphorylate primarily on serine residues, is activated by bovine calmodulin and additional evidence from phase partitioning indicate most of this enzyme to be located in the plasma membrane.
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  • 72
    ISSN: 1432-0878
    Keywords: Ionophore A-23187 ; Calcium ; Exocrine pancreas ; Secretion ; Zymogen granule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Rat-pancreas lobules were incubated with the ionophore A-23187 in the presence of Ca2+. After 90 min, some of the acini were partially or almost completely depleted of their zymogen granules while others had the appearance of resting acini. With few exceptions, the cells of a given acinus were degranulated to a comparable level. Slight dispersion of the zymogen granules was noticed in cells incubated in a Ca2+-free medium containing EGTA with or without A-23187. In the presence of Ca2+ the secretory response obtained with the ionophore was comparable to that observed with 10-5M urecholine. The results obtained provide cytological evidence that the secretory response is only partially determined at the membrane-receptor level and that other mechanisms intervene between cytosol Ca2+ increase and exocytosis.
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  • 73
    ISSN: 1432-0878
    Keywords: Carotid body ; Calcium ; Granular vesicles ; Exocytosis
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Summary An attempt was made to study the subcellular localization of calcium in carotid body glomus cells of adult rats using fixation with glutaraldehyde followed by treatment with a mixture of pyroantimonate and osmium tetroxide. Precipitates were seen as electron-dense particles (EDP) in the glomus cells, mostly within membrane-bound organelles, such as dense-cored vesicles, mitochondria, small clear vesicles, multivesicular bodies, and especially in lysosomes. However, EDP were also seen in the nuclei and in the free cytoplasm of the glomus cells and even outside them. Preincubation of carotid bodies in media containing calcium and either high potassium or calcium-ionophore A 23187 resulted in a marked increase in the general precipitation pattern, there being an increased amount of EDP both in the glomus cell nuclei and in the cytoplasm. Dense-cored vesicles more often showed precipitates than those in the controls. Some dense-cored vesicles contained multiple precipitates, typically located in the electron-lucent area between core and vesicle membrane. Extensive diffusion of ions probably occurred during fixation before precipitation, making the localization of calcium and other precipitating cations unreliable. However, it is possible that precipitates, which were regularly seen in the dense-cored vesicles, may reflect the content of bound calcium. The possible significance of calcium in glomus cell function is discussed, and the need for more adequate methods is emphasized.
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  • 74
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    Cell & tissue research 246 (1986), S. 183-187 
    ISSN: 1432-0878
    Keywords: Neonate ; Paneth cells ; Corticosteroid ; Zinc ; Calcium ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Paneth cells containing zinc-rich granules were found in the small intestine of 6-day-old rats. These cells were more numerous in older animals and were consistently most common in the distal ileum. The zinc content of granules from 10-day-old rats was similar to that found in adults (ca 300 mg atoms/kg dry weight) but no calcium could be detected. An injection of cortisone acetate at 5 days resulted in a premature increase in the numbers of Paneth cells in 10-day-old rats. The cell granules contained normal, adult levels of zinc, a calcium concentration of ca 400 mg atoms/kg dry weight and also an increased concentration of phosphorus.
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  • 75
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    Cell & tissue research 236 (1984), S. 237-244 
    ISSN: 1432-0878
    Keywords: Aster formation ; Calcium ; Endoplasmic reticulum ; Hypertonic stress ; Parthenogenetic stimulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Sea urchin eggs exposed to a continuous hypertonic treatment rapidly form many concentric whorls of endoplasmic reticulum (ER) during the pre-activation period of the parthenogenetic development. These whorls, however, are only a temporary configurational alteration of ER which begin to break up just prior to egg activation. The conversion back to normal vesicles and lamellae occurs not only concurrently with the appearance of early cytastral areas, but also frequently in close association with the formation of these membranous areas. It is revealed here that membrane elements from disrupting whorls may become incorporated into adjacent, developing clear areas, early cytastral areas, and that this ER constitutes an initial major source of membranes for these early astral areas. Having previously suggested that the actual formation of ER whorls occurs in direct response to released intracellular calcium in hypertonic stressed eggs, the new findings, along with other related data and correlations, further suggest that whorl disruption and the formation of associated astral areas can be correlated with a corresponding decrease in the concentration of this released calcium in the cytoplasm.
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  • 76
    ISSN: 1432-0878
    Keywords: Photoreceptors ; Calcium ; Fixation artifact ; Light-adaptation
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Summary The conditions that lead to the formation of myelin figures in rhabdomere microvilli were studied in the larval ocelli of the mosquito Aedes aegypti. These artifacts can result from the addition of divalent ions, such as Ca2+, to primary-aldehyde fixatives, but they form subsequently during postfixation with OsO4. In light-adapted ocelli, myelin figures are concentrated at the proximal ends of the microvilli along the cytoplasmic margin of the rhabdomere. The severity of the artifact is proportional to the ion concentration: scattered myelin whorls are induced by Ca2+ concentrations as low as 5 mM; they become abundant at 15 mM to 25 mM, and displace much of the rhabdomere margin at 50 mM. In contrast, even at high concentrations of Ca2+ few membrane whorls form in dark-adapted rhabdomeres, and these are mostly located at the distal ends of the microvilli. The differential response of the rhabdomere microvilli in light and darkness does not result from a direct action of light during fixation; it reflects an underlying difference between light- and dark-adapted photoreceptor membranes. We suggest that this differential sensitivity to divalent ions is associated with the shedding of membranes from the rhabdomere, a process that is enhanced by light and reduced in darkness.
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  • 77
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    Cell & tissue research 242 (1985), S. 557-564 
    ISSN: 1432-0878
    Keywords: Phagocytosis ; Amoeba proteus ; Glutathione ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The process of phagocytosis in Amoeba proteus was examined by following the uptake of Tetrahymena pyriformis and agarose beads. The ciliates are taken up in a time dependent and saturable manner. T. pyriformis apparently emits a water-soluble substance that acts as a chemoattractant to the amoebae. Plain agarose beads are not engulfed by A. proteus, but those beads having reducedglutathione with the -SH group exposed are taken up almost to the same extent as T. pyriformis. Phagocytosis of the glutathione beads is calcium-dependent with maximum bead uptake at 10-4M Ca++. Glutathione applied to A. proteus brings about pseudopod formation, increased phagocytosis and displacement of surface-associated calcium.
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  • 78
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    Cell & tissue research 245 (1986), S. 599-604 
    ISSN: 1432-0878
    Keywords: Osmoregulation ; Mucus ; Intestine ; Biocrystallization ; Calcium ; Anguilla anguilla
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Freeze-dried intestinal mucus of sea-water-adapted eels was analysed by scanning electron microscopy (SEM) and X-ray microanalysis. Calcite crystals were observed in the mucus fibres; their concentration increased along the hindgut. Random SEM observations made in situ indicated that mucus fibres were involved in the genesis of these crystals. Calcium-rich mucus globules were found fused inside crystal matrices. Single typical rhombohedric crystals of various complexity appeared within the mucus framework. The steps of crystal biogenesis were reconstituted in in-vitro conditions.
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  • 79
    ISSN: 1432-0878
    Keywords: Mantle dentin matrix ; Electron spectroscopic imaging (ESI)-analysis ; Calcium ; Phosphorus ; Dentinogenesis ; Biomineralization ; Rat (Wistar)
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Summary The subcellular distribution of the inorganic elements calcium (Ca) and phosphorus (P) was studied in the first-formed dentin matrix during initial mineralization in neonatal rat molars. This most peripheral matrix region is comprised of a proteoglycan-rich ground substance, interwoven by a collagenous network, matrix vesicles, aperiodic fibrils derived from the dental basal lamina, and apical odontoblastic cell processes. All matrix components may possibly serve as templets for mineral deposition during initial calcification of first-formed mantle dentin and predentin. By means of the very sensitive ESI-analysis we studied the subcellular localization of Ca and P and their possible association with distinct organic extracellular matrix components and odontoblasts. Ca-signals were found in the ground substance, at striated collagen fibrils and plasma membranes of odontoblasts in the cuspal early matrix region, but occurred only sparsely in the ground substance of the more distal matrix region where odontoblast processes attach to aperiodic fibrils of the dental basal lamina. Ca was generally absent in matrix vesicles. In contrast, P-signals were found in matrix vesicles, at aperiodic fibrils and at the plasma membranes of odontoblasts. Ca and P co-localized at striated collagen fibrils (type I or II). These results suggest that striated collagen fibrils might serve as primary deposition sites for calcium phosphate during early biological calcification of organic extracellular macromolecules.
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  • 80
    ISSN: 1432-0878
    Keywords: Auditory system ; Vocal motor system ; Parvalbumin ; Cytochrome oxidase ; 2-Deoxyglucose ; Calcium ; Plasticity ; CNS ; Song birds ; Zebra finch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The auditory and vocal motor systems of adult zebra finches were investigated 1) immunocytochemically for the distribution of the Ca2+-binding protein parvalbumin, 2) for the activity of the respiratory enzyme cytochrome oxidase, and 3) for the uptake of 2-deoxyglucose. All auditory nuclei (field L, nucleus ovoidalis, ansa lenticularis, nucleus spiriformis lateralis, nucleus mesencephalicus lateralis-pars dorsalis, nucleus tegmenti pedunculo-pontinus) and vocal motor nuclei (nucleus magnocellularis of the anterior neostriatum, area X, nucleus interfacialis, hyperstriatum ventrale-pars caudalis, nucleus robustus archistriatalis, nucleus intercollicularis) showed high levels of parvalbumin and cytochrome oxidase. Auditory nuclei in addition showed high spontaneous 2-deoxyglucose uptake, while the vocal motor nuclei either remained at background intensity (nucleus magnocellularis of the anterior neostriatum, hyperstriatum ventrale-pars caudalis, nucleus interfacialis and nucleus intercollicularis) or even below background levels (area X, nucleus robustus archistriatalis). Cytochrome oxidase activity supposedly reflects the energy demand of various aspects of metabolism, while 2-deoxyglucose uptake is primarily related to the demands of electrical activity and the Na+-K+ pump. Consequently, it is argued (i) that the congruently high cytochrome oxidase activity and 2-deoxyglucose uptake in the auditory system are due to the high spontaneous electrical activity of neurons, and (ii) that high cytochrome oxidase activity in vocal motor nuclei is related to other than electrical events since 2-deoxyglucose uptake is low. There is evidence of Ca2 + potentials in some parvalbumin-positive neuron types. Ca2+ potentials must lead to Ca2+ flooding of the cytoplasm which could be buffered by parvalbumin thus preventing interference with Ca2+ dependent metabolic reactions or shuttling the ion to sites of such reactions. The unique morphological plasticity reported from the parvalbumin-positive vocal motor nuclei may put a strain on microtubular transport which is Ca2+ dependent. This leads to the idea that parvalbumin reflects local buffering and redistribution mechanisms for Ca2+, and that cytochrome oxidase indicates the underlying energy demand.
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  • 81
    ISSN: 1432-0878
    Keywords: Pituitary ; Pars intermedia ; Calcium ; Deionized water ; Teleosts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Cytological changes in the pars intermedia of the goldfish were investigated after adding calcium to deionized water (DW). In fish maintained in DW, the PAS-positive cells are highly stimulated in comparison to cells of fish kept in fresh water (FW). In DW supplemented with calcium at the same concentration as in FW (2 mM/l), the hyperactivity of the PAS-positive cells is prevented. When calcium ions are added 60 h before the animals are sacrificed, the PAS positive cells start to show signs of regression and their granules are stored: the release of the granular material appears to be suppressed by calcium. In the goldfish, the PAS-positive cells, homologous to a similar cell type in the eel, react only very weakly with the PAS technique. The name “calcium-sensitive cells” appears to be more appropriate in the goldfish for this particular cell type, secreting an unknown factor. This factor, different from the prolactin produced in the rostral pars distalis of the hypophysis, might be an equivalent of a “hypercalcin”.
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    Cell & tissue research 213 (1980), S. 9-20 
    ISSN: 1432-0878
    Keywords: Pinocytosis ; Calcium ; Chlorotetracycline ; Fluorescence microscopy ; Amoeba proteus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The dynamics of Ca++ during induced pinocytosis were studied in Amoeba proteus using chlorotetracycline (CTC). The fluorescence of the Ca++ -CTC-complex was monitored by an image intensification system, which has certain advantages over standard equipment: (1) Living cells are not subjected to the damaging influence of intensive microscopic illumination, (2) fluorescent probes are not bleached during observation, and (3) the rapid dynamics of Ca++-fluxes can be recorded using short exposure times. The results demonstrate the existence of Ca++ bound to intracellular and extracellular sites of the cell membrane complex in normal locomoting and pinocytoting Amoeba proteus. The application of cations inducing pinocytosis causes a rapid decrease in the external CTC-fluorescence probably due to a release of Ca++ from the mucous layer. The degree of fluorescence intensity is correlated with the capacity of pinocytotic channel formation, i.e., the fluorescence decreases as the number of channels increases. During the phase of vesiculation a distinct fluorescence mainly restricted to the basal region of the channels is observed. Intracellular Ca++ was detected in close vicinity to the plasma membrane after both microinjection and external application of CTC. The internal CTC-fluorescence is slightly decreased during the induction phase of pinocytosis. The observations are in good agreement with previous results on the localization of Ca++-binding sites at the plasma membrane of Amoeba proteus and demonstrate the important role of Ca++-fluxes for the process of pinocytosis.
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  • 83
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    Cell & tissue research 247 (1987), S. 633-637 
    ISSN: 1432-0878
    Keywords: Scale ; Amoeba ; Mineral component ; Calcium ; X-ray microanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Mineral components of the scales in an amoeba, Cochliopodium sp., were examined by energy-dispersive X-ray microanalysis. The precipitates in potassium antimonate-treated material detected calcium in the scales. Calcium was also clearly detected in freeze-substituted thin sections. Similar deposits of calcium antimonate were detected in scales in formation within vacuoles, and also in Golgi cisternae, Golgi vesicles and special granules near the nucleus. There were only minute amounts of magnesium and potassium. This suggests that calcium is the main mineral component of the scales and that it is added in the Golgi complex during scale formation.
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  • 84
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    Cell & tissue research 250 (1987), S. 589-593 
    ISSN: 1432-0878
    Keywords: Phagocytosis ; Chemotactic peptides ; Calcium ; Amoeba proteus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The tripeptide n-formylmethionylleucylphenylalanine (NFMLP) at low levels (10−9 M) localized in a glass micropipette elicits a positive chemotactic response in Amoeba proteus. Peptide in solution at higher concentrations (10−5 M) stimulates food vacuole formation. Vacuoles induced by NFMLP result from the fusion of pseudopods which, in turn, entrap a portion of the external medium. Food vacuole formation stimulated by NFMLP is dependent on the concentration of calcium in the external medium. The binding of NFMLP to the amoeba surface may bring about a movement of calcium into the cell which can be inhibited with calcium-channel blockers.
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  • 85
    ISSN: 1432-0878
    Keywords: Calcium ; Parvalbumin ; Calbindin D-28K ; S-100 proteins ; Calmodulin ; Testis ; Male sexual hormones ; Leydig cells ; Spermatogenesis ; Rat (SIV-50)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Calcium and intracellular Ca2+-binding proteins are possibly involved in hormone production and spermatogenesis in rat testis. Parvalbumin, calbindin D-28K, S-100 proteins and calmodulin were localized in the Leydig cells, which are sites of testosterone synthesis. Only the appearance of parvalbumin-immunoreactivity is closely correlated to testosterone production during development of the testes. Calbindin D-28K-immunoreactivity persisted in foetal-type Leydig cells and in adult-type Leydig cells at all stages of development. S-100-immunoreactivity was low during all foetal stages, absent between birth and puberty, and increased thereafter. Calmodulin staining is most prominent in the cytoplasm of developing spermatocytes and of maturing spermatids. All four proteins co-exist in the seminiferous tubules. The distinct localization and developmental appearance of these proteins suggests different regulatory roles in Leydig cell function and spermatogenesis.
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    Cell & tissue research 253 (1988), S. 447-455 
    ISSN: 1432-0878
    Keywords: Lysosomes ; Muscle damage ; Calcium ; Lysosomotropic agents ; Phospholipase A2 ; Frog (Rana temporaria) ; Guinea pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Experiments with lysosomotropic agents suggest that the sarcotubular system subserves some of the functions of the lysosomal apparatus in frog skeletal muscle. Dinitrophenol or A23187 trigger lysosome labilization and myofilament damage in mammalian cardiac muscle. Lysolecithin labilizes isolated liver lysosomes, but has no action following phospholipase A2 activation in vivo. Zinc ions or a pHi of 7.5 do not protect against myofilament damage. In fractions from mammalian cardiac muscle, calcium and calmodulin do not cause lysosomal labilization whereas cGMP does but only at high concentration (10-4 M). It is concluded that lysosomal hydrolases play no significant part in rapid muscle damage. It is suggested that rises in [Ca]i activate two separate pathways causing (i) myofilament damage; (ii) sarcolemmal (and possibly lysosomal) membrane damage via phospholipase A2 and lipoxygenase activity. Dinitrophenol triggers both pathways independently and thus may cause lysosome labilization. The possibility that the sarcoplasmic reticulum is the site generating myofilament damage is discussed.
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    Cell & tissue research 253 (1988), S. 457-462 
    ISSN: 1432-0878
    Keywords: Muscle damage ; Cardiac muscle ; Calcium ; Phospholipase A2 ; Lipoxygenase ; Cyclo-oxygenase ; Rana ttemporaria ; Mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary This study compares the action of inhibitors of the eicosanoid cascade on calcium-induced myofilament damage in cardiac muscle of the perfused frog heart and incubated frog ventricle slices, and in skeletal muscle of incubated mammalian diaphragm and isolated and saponin-skinned amphibian pectoris cutaneous muscle. Mepacrine (10-5M) and indomethacin (3×10-6M) protected completely against myofilament damage induced by entry of calcium in the ‘calcium-paradox’ in frog heart. However, inhibition of phospholipase A2 (PLA2) (with chlorpromazine, 2×10-4M, or mepacrine, 10-5M, 5x10-5M), of cyclo-oxygenase enzymes (with indomethacin, 3x10-6M to 10-5M or BW755C, 3.8x10-4M), or of lipoxygenase enzymes (with BW755C, 3.8x10-4M or nordihydroguaiaretic acid, 2x10-6M or 5x10-6M) all failed in intact cardiac or skeletal muscle cells to prevent the myofilament damage that is rapidly triggered by 10-2M caffeine, 6x10-6M ruthenium red, 10-4M DNP or 5 μg ml-1 A23187. These agents also failed completely to protect against myofilament damage in saponin-skinned amphibian skeletal muscle when [Ca]i was raised to 8x10-6M. Thus, inhibition of PLA2 does not protect the myofilament apparatus against calcium released intracellularly, and it is suggested that mepacrine and indomethacin can block entry of calcium in the calcium-paradox in the amphibian heart. Chlorpromazine (2x10-4M) and mepacrine (10-3M) at zero [Ca] caused severe myofilament damage in skinned muscle, possibly due to an effect on membranes. Since inhibitors of PLA2 and of lipoxygenases prevent efflux of creatine kinase and sarcolemma damage in mammalian skeletal muscle, it is evident that experimentally-induced rises in [Ca]i (by caffeine or A23187) can trigger two separate pathways: (i) PLA2 and the arachidonic acid cascade which culminate in membrane damage, and (ii) a different, Ca-activated system that causes rapid damage of myofilaments.
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  • 88
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    Protoplasma 130 (1986), S. 199-205 
    ISSN: 1615-6102
    Keywords: Calcium ; Crystals ; Energy dispersive X-ray analysis ; Lemna minor ; Oxalate ; Strontium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Lemna minor, which produces many calcium oxalate raphide crystals, was grown on media containing in addition to Ca, 200 μM of one of the following divalent cations: Ba, Cd, Co, Mn or Sr. Energy dispersive X-ray analysis showed that only Sr was incorporated into the raphides at levels detectable by the analysis technique. Incorporation of Sr into other insoluble compounds, such as cell wall material, could not be detected. Plant species which form different crystal types in their leaves (Beta vulgaris, crystal sand;Arthrostema ciliatum, druse;Glycine canescens, prismatic) also incorporated Sr into their crystals when grown hydroponically on nutrient medium containing 200 μM Sr. Axenic cultures ofL. minor were used to examine further the process of Sr incorporation into plant crystals. When grown on nutrient solution with 5 μM Ca, increasing the Sr concentration resulted in increases of the amount of Sr incorporated into the raphide crystals. The ratio of Sr to Ca became greater as the Sr concentration was increased. This ratio change was due to both an increase in the amount of Sr incorporated and a decrease in the Ca incorporated. Analysis of the number of crystal idioblasts formed as a function of Sr concentration shows fewer idioblasts are produced as Sr became high. Competition with Ca and interference of Ca utilization by Sr is indicated.
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  • 89
    ISSN: 1615-6102
    Keywords: Calcium ; Cell elongation ; Indole-3-acetic acid ; Pisum sativum ; Secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The treatment of dark grown pea stem segments with chelators of divalent cations (EGTA, EDTA, CTC), various Ca2+ antagonists (LaCl3, A-23187, verapamil) and inhibitors of secretory processes (monensin, CB) reduced elongation in the presence of indole-3-acetic acid (IAA). Generally the inhibition increased with increasing concentrations of the substances. The timing of the responses can be correlated with maximum auxin-stimulated secretion of cell wall material. Examination of cell ultrastructure showed that changes in dictyosome activity could explain a reduced deposition of cell wall material and so cause inhibition of elongation. The inhibitors affected the morphology and vesiculation of the dictyosomes, and the appearance of the plasma membrane, ER and mitochondria in different ways. The most pronounced effects on ultrastructure resulted from monensin and LaCl3 treatments with the dictyosomes being most affected; large vesicles appeared in the cytoplasm. Less pronounced effects on cell structure were seen in EGTA, A-23187 and verapamil treated tissue. The effects on the dictyosomes are considered to be due to disturbances of Ca2+ and other ionic levels within the cells.
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  • 90
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    Protoplasma 115 (1983), S. 11-17 
    ISSN: 1615-6102
    Keywords: Pollen tubes ; Calcium ; Tip extension ; Vesicle fusion ; Microfilaments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Pollen tube growth is shown to be inhibited by both suboptimal (〈10−4 M) and supraoptimal (〉10−3 M) Ca2+ ion concentrations. Tip extension rates are independent of Ca2+ ion concentration over the optimal range. Changes in the structure of the tips of pollen tubes after transfer to inhibitory Ca2+ ion conditions provide evidence in support of our proposed mechanism of pollen tube tip growth (J. theor. Biol.98, 15–20, 1982). It is clearly demonstrated that tip extension is controlled, not only by the rate of vesicle fusion, but also by the state of plasticity of the tip; these processes appear to be sensitive to changes in Ca2+ ion concentration.
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  • 91
    ISSN: 1615-6102
    Keywords: Calcium ; Contraction ; Discophrya ; Ionophore A 23187 ; Ruthenium red ; Tentacle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The suctorian protozoonDiscophrya collini has contractile tentacles with microfilaments and a central microtubule-lined canal (axoneme). The role of calcium fluxing in tentacle contraction has been investigated using the Ca2+ ionophore A 23187 and ruthenium red (RR), a known inhibitor of certain Ca2+ membrane transport events. Treatment with CaCl2 alone caused tentacle contraction with a threshold at 5 × 10−3 M CaCl2 and a maximum at 5 × 10−2 M CaCl2 with contraction to 32.8% of the original length. In the presence of 5 μM ionophore A 23187 the threshold was lowered to 5 × 10−6 M CaCl2 with a maximum to 19.6% original length at 5 × 10−2 M CaCl2. A 23187 alone induced contraction with a threshold of 3.0 μM and a maximum to 30.5% original length at 10 μM A 23187. Treatment with RR alone had little effect on tentacle length. However, a 10 μM A 23187-induced contraction was partially counteracted by the simultaneous application of RR with a threshold at 2 μM RR and a maximum at 8 μM RR. Removal of the ionophore after induced tentacle contraction resulted in partial re-extension, which was inhibited by RR. Ultrastructural observations indicated that the ionophore and CaCl2-induced contraction processes are indistinguishable. The CaCl2/ionophore treatments led to axonome disruption, interpreted as a consequence of supranormal levels of intracellular Ca2+. X-ray microanalysis of cytoplasmic membrane-bound elongate dense bodies (EDB) showed a high level of Ca2+ in CaCl2-treated cells, little Ca2+ in ionophore-treated cells and intermediate levels in the RR-treated, ionophore/RR-treated and untreated control cells. It is suggested that A 23187 enhances both the uptake of extracellular Ca2+ and the release of Ca2+ from the EDB, the latter being counteracted by RR. These observations support the proposal that the EDB act as Ca2+ reservoirs, and that their Ca2+ fluxing moderates cytosolic Ca2+ levels which mediate a Ca2+-dependent tentacle contraction mechanism.
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  • 92
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    Protoplasma 117 (1983), S. 226-232 
    ISSN: 1615-6102
    Keywords: Calcium ; Calmodulin ; Chlorotetracycline ; Microfluorometry ; Phenothiazine ; Pollen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Pear (Pyrus communis L.) pollen was germinated and grown in hanging drop cultures containing phenothiazine drugs, trifluoperazine and chlorpromazine, potent inhibitors of the Ca2+-calmodulin complex. Responses for the two drugs were similar: at 1.0–2 10.0 ΜM pollen germination and tube growth were inhibited. Inhibition of tube growth was not uniform; at 10.0 ΜM growth of about half of those tubes which had germinated was inhibited while the remaining half of the population grew normally. This bimodal distribution of tube growth was noted, but to a lesser extent, at lower concentrations of the drugs as well. Microfluorometric analysis of membrane calcium using chlorotetracycline, a fluorescent chelate probe for membrane calcium, revealed that upon pollen grain hydration there was a sharp decrease in the concentration of calcium associated with membranes and that membrane calcium became localized primarily at the periphery of the newly hydrated pollen grain. Prior to germination there was a reloading of calcium onto membranes in the region of the germination aperture through which the pollen tube would emerge. The release of Ca2+ from membrane sites upon hydration was partially inhibited by treatment with 10 ΜM trifluoperazine. Distribution of membrane calcium in populations of the inhibitor-treated pollen grains was not bimodal however; approximately half of the population had CTC-fluorescence emissions exceeding the maximum value found in the control population. These results suggest that there is a maximum concentration of membrane-associated calcium consistent with normal pollen germination and tube growth and that phenothiazines interfere with the unloading of Ca2+ from membrane sites.
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  • 93
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    Protoplasma 120 (1984), S. 209-215 
    ISSN: 1615-6102
    Keywords: Fusion ; Calcium ; Protoplast ; Membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Rather than selecting for a chemical fusogen one can select for a fusogenic plant membrane (i.e., one that will fuse readily). Wild carrot suspension culture cells can be grown under conditions which cause the released protoplasts to have a high potential to fuse. Protoplast fusion is enhanced by calcium and inhibited by EGTA. When 10mM calcium (pH6.0) is added, fusion percentages of 60% are common. The mild fusion treatment appears to have no effect on callus regeneration and differentiation.
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  • 94
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    Protoplasma 152 (1989), S. 46-56 
    ISSN: 1615-6102
    Keywords: Calcium ; Fluorescence photobleaching recovery ; Lateral diffusion ; Lipid phase ; Plasma membrane ; Protoplast regeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Lateral diffusion measurements have been made on lipids and proteins in the plasma membrane of live protoplasts derived from rose (Rosa sp. “Paul's Scarlet”) suspension-cultured cells. Two different fluorescent lipid probes exhibited markedly different diffusion rates, indicating possible heterogeneity in the lipid domain of the membrane. Membrane proteins were labeled directly with covalently-reactive fluorophores, and factors that might perturb the lateral diffusion of these labeled proteins were investigated. Treatment of the protoplasts with various cytoskeleton-disrupting drugs generally had little effect on protein diffusion, although treatment with oryzalin, a microtubule-disrupting drug, did slightly reduce the mobile fraction of membrane proteins. Elevation of the CaCl2 concentration in the medium from 1 mM to 10 mM significantly reduced the mobile fraction of membrane proteins and also increased the fraction of protoplasts that were able to regenerate cell walls and divide in culture. These results are discussed in relation to reported evidence of lipid domains in the plasma membranes of other cells and protoplasts. The relative importance of lipid domains and membrane-cytoskeleton interaction in governing protein diffusion is considered.
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  • 95
    ISSN: 1615-6102
    Keywords: Dictyostelium discoideum ; Cellular slime moulds ; Calcium ; Cyclic AMP ; Chemotaxis ; Differentiation ; Slug movement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Intracellular free calcium ion concentrations ([Ca2+]i) in the anterior prestalk and posterior prespore cells of theDictyostelium discoideum slug were determined, using the highly selective Ca2+ indicators, quin-2/AM and fura-2/AM. Temporal changes in [Ca2+]i in response to chemotactic stimulation with cAMP were also monitored at the single-cell level and compared between the two types of cells. The results obtained showed that resting [Ca2+]i in the prestalk cells is considerably higher than that in the prespore cells. Moreover, transient increase in [Ca2+]i upon stimulation with a low concentration of cAMP (20 nM) was noticed only in the prestalk cells, but not in the prespore cells. These facts are discussed in relation to the polarized movement and cellular differentiation in the migrating slug.
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  • 96
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    Protoplasma 109 (1981), S. 169-185 
    ISSN: 1615-6102
    Keywords: Actomyosin ; Anchorage sites ; Calcium ; Chloroplast movement ; Mougeotia sp. ; Phytochrome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The single, ribbon-shaped chloroplast in the filamentous green algaMougeotia performs orientational movements with respect to light. The chain of reaction involves phytochrome as the photoreceptor pigment to perceive the light signal differentiated by wavelength and direction, calcium probably to convert the light signal into a chemical message and actomyosin to respond to this message and to move the chloroplast accordingly.Precise reorientation of the chloroplast is proposed to be brought about by a dual function of phytochrome: regulation of the cellular level of calciumand regulation of membrane anchorage sites to actin.
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  • 97
    ISSN: 1615-6102
    Keywords: Aequorin ; Calcium ; Characeae ; Lamprothamnium ; Turgor regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In internodal cells ofLamprothamnium succinctum, turgor regulation in response to hypotonie treatment is inhibited by lowering external Ca2+ concentration ([Ca2+]e) from 3.9 (normal) to 0.01 (low) mM. In order to clarify whether a change in the cytoplasmic free Ca2+ concentration ([Ca2+]c) is involved in turgor regulation, the Ca2+ sensitive protein aequorin was injected into the cytoplasm of internodal cells. A large transient light emission was observed upon hypotonic treatment under normal [Ca2+]e but not under low [Ca2+]e. Thus hypotonic treatment induces a transient increase in [Ca2+]c under normal [Ca2+]e but not under low [Ca2+]e.
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  • 98
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    Protoplasma 140 (1987), S. 92-99 
    ISSN: 1615-6102
    Keywords: Calcium ; Dantrolene-Na ; Excoytosis ; Nifedipine ; Paramecium ; Trichocyst ; Trifluoperazine ; Verapamil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Ca2+ dependent exocytosis inParamecium involves the release of numerous secretory organelles known as “trichocysts”. According toGarofalo et al. (1983) trichocysts pass through three stages of condensed (tmxI), partially expanded (stage II) before release, and fully expanded (stage III) or released trichocysts. We have therefore investigated the effect of two widely used Ca2+ channel blockers, verapamil and nifedipine and the muscular relaxant, dantrolene-Na, on the process of trichocyst release. Verapamil and nifedipine inhibited secretion in a dose dependent manner, but dantrolene-Na and the solvent, PEG-400, did not abolish it. Electron microscopic study of preincubatedParamecium cells in verapamil resulted in the appearance of tmxI, whereas untreated controls remained in partially expanded stage II. Pretreatment of isolated membrane free trichocysts with verapamil did not inhibit matrix expansion in the presence of increasing Ca2+ concentration. In a separate experiment, cells were pretreated with verapamil and the anti calmodulin compound, trifluoperazine. The cells were then induced to release their secretory contents by picric acid-Ca2+ treatment. Electron microscopic examination of cells captured by quick fixation with osmium tetroxide revealed that verapamil treated cells manifested the inhibition of membrane fusion, whereas in TFP treated cells there was no sign of a traceable exocytotic opening formation after membrane fusion. Based on present results we propose a role for calmodulin in the formation of exocytotic openings.
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    Protoplasma 146 (1988), S. 118-126 
    ISSN: 1615-6102
    Keywords: Bioelectricity ; Calcium ; Polarity ; Hyphal growth ; Allomyces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In contrast to all filamentous fungi examined to date, vegetative hyphae ofAllomyces macrogynus, whether extending or not, produced an outward flow of positive electrical current, at a maximum of 0.16 μA cm−2 around 40 μm behind the apex, as measured with a vibrating probe. Inward currents of up to 0.55 μA cm−2 were recorded around the rhizoids. Increases in outward current were observed in hyphae pre-grown under oxygen deficiency and then allowed to widen backwards to the hyphal base in sufficient oxygen. When spores were germinated in an applied electrical field they produced rhizoids predominantly towards the anode. Hyphae were produced initially towards the cathode but later bent around towards the anode. Experiments with a range of chemicals provided no evidence for the involvement of calcium in vegetative growth and development inA. macrogynus. Polyoxin and nikkomycin, inhibitors of chitin synthesis, had no effect on swimming zoospores, but inhibited wall formation of cysts, rhizoids and forward and backward growing hyphae.
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    Protoplasma 149 (1989), S. 24-30 
    ISSN: 1615-6102
    Keywords: Adhesion ; Calcium ; Lectins ; Phytophthora cinnamomi ; Secretion ; Zoospore
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary During encystment,Phytophthora cinnamomi zoospores bind firmly to the host surface. We have developed a microassay to study adhesion of the zoospores to solid surfaces, both biological and non-biological. The results show that timing of the acquisition of adhesiveness during encystment correlates closely with the secretion of high molecular weight glycoproteins. The adhesive phase is short lived, occurring between 1 and 4 min after induction of encystment. During this period, cells that come into contact with a variety of surfaces (glass, plastic, and onion epidermis) become firmly attached, while cells that come into contact with one of these substrata after this period are unable to bind. Our results also show that EGTA inhibits cyst adhesion, while addition of calcium promotes cyst adhesion, especially of cysts more than 4 min old. To help identify the cyst surface component involved in adhesion we tested a number of lectins for their ability to block cyst adhesion. Soybean agglutinin andHelix pomatia agglutinin, lectins which bind to the secreted high molecular weight glycoproteins, both inhibit adhesion in the presence and absence of the hapten sugar, indicating that inhibition was non-specific. Wheatgerm agglutinin, a lectin which does not bind to the cyst surface, also blocked adhesion non-specifically.
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