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  • Calcium  (36)
  • Springer  (36)
  • American Chemical Society
  • Annual Reviews
  • Elsevier
  • 1995-1999  (16)
  • 1980-1984  (20)
Collection
Keywords
Publisher
  • Springer  (36)
  • American Chemical Society
  • Annual Reviews
  • Elsevier
  • Wiley-Blackwell  (1)
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Calcium-induced sperm fusion in Zea mays L. (1997)
    Springer
    Sexual plant reproduction 10 (1997), S. 74-82 
    Details
    ISSN: 1432-2145
    Keywords: Key words Zea mays ; Calcium ; Sperm fusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In this study, we examined morphological changes of isolated maize (Zea mays L.) sperm cells in the presence of Brewbaker and Kwack salts (BKS) or the individual components of BKS using light, transmission electron and scanning electron microscopy. Freshly isolated sperms are 7.5 μm in diameter. Treatment with BKS for 5 h resulted in large cells with a diameter up to 41 μm. Staining of sperm nuclei with 4′, 6-diamidino-2-phenylindole (DAPI) revealed two or more nuclei in a single cell, suggesting that BKS induces cell fusion. Treatment with each BKS component showed that cell fusion occurs only in the presence of calcium nitrate. Use of several calcium salts showed the same results, suggesting that the calcium ion, alone, is responsible for the observed cell fusion. Further studies were conducted to examine the relationship between calcium distribution and sperm location in pollen tubes using chlorotetracycline and DAPI. Growing maize pollen tubes exhibited a high membrane calcium region within 20–50 μm from the tip. The Sperms are found no closer than 90 μm to the tip of the tube, suggesting that sperms are located in a low calcium region prior to being released to the degenerating synergid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004970050070
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  • 2
    Electronic Resource
    Electronic Resource
    Rhythmic dentinogenesis in the rabbit incisor: Allometric aspects (1980)
    Springer
    Calcified tissue international 32 (1980), S. 45-53 
    Details
    ISSN: 1432-0827
    Keywords: Dentin ; Periodicity ; Allometry ; Calcium ; Sulfur
    Source: Springer Online Journal Archives 1860-2000
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02408520
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  • 3
    Electronic Resource
    Electronic Resource
    Rhythmic dentinogenesis in the rabbit incisor: Circadian, ultradian, and infradian periods (1980)
    Springer
    Calcified tissue international 32 (1980), S. 29-44 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02408519
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of calcium, magnesium, potassium and boron on sperm cells isolated from pollen of Zea mays L. (1995)
    Springer
    Sexual plant reproduction 8 (1995), S. 113-122 
    Details
    ISSN: 1432-2145
    Keywords: Zea mays ; Calcium ; Cell integrity ; Cell viability ; Sperm cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Our previous studies showed that Brewbaker and Kwack salts, which have been widely used in pollen germination and sperm isolation, are not appropriate for the maintenance of isolated maize (Zea mays L.) sperm cells. In the present study, we have characterized the effects of each BKS component salt on the integrity of isolated sperm cells using hemacytometry. At 0.01 and 0.1 mM, there were no differences in cell number between control and any salt-treated cells except a 22% decrease with 0.1 mM MgSO4 at 48 h. At the 1 mM level, cell number decreased with time in the presence of Ca(NO3)2 and MgSO4, with loss of integrity of most cells at 48 h, while KNO3 and H3BO3 had little or no effect. Further characterization of calcium-induced reduction in cell integrity using flow cytometry showed that depletion of possible residual free calcium by addition of EGTA to the suspension medium improved cell longevity and viability. Exposure of isolated sperm cells to 1 mM calcium had no effect on cell integrity and viability in 5 h; however, only 12% of cells remained intact at 24 h. The reduction in cell integrity was hastened when cells were pretreated with the calcium ionophore A23187 prior to exposure to 1 mM calcium, with a 54% reduction in cell number at 1 h and complete cell lysis at 24 h. However, depletion of cytosolic free calcium by pretreatment of cells with the calcium ionophore followed by resuspension in the presence of EGTA resulted in rapid reduction of cell integrity as well. These results collectively suggest that maize sperm cells are sensitive to exogenous free calcium; however, a certain level of cytosolic free calcium is necessary for maintenance of integrity. Mechanisms of calcium-induced reduction in cell integrity are discussed along with possible roles of the sensitivity of sperm cells to calcium in fertilization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230898
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  • 5
    Electronic Resource
    Electronic Resource
    Tentacle contraction inDiscophrya collini: The effects of ionophore A23187 and ruthenium red on Ca2+-induced contraction and uptake of extracellular calcium (1984)
    Springer
    Protoplasma 122 (1984), S. 125-131 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Contraction ; Discophrya ; Ionophore A23187 ; Ruthenium red ; Tentacles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The tentacles of the suctorian protozoonDiscophrya collini are stimulated to contract by externally applied Ca2+. The role of extracellular Ca2+ in tentacle contraction was studied by monitoring45Ca2+ uptake, using ionophore A23187 to facilitate membrane transport of calcium and ruthenium red (RR) as an inhibitor of transport. The degree of tentacle retraction was dependent upon external Ca2+ concentration and studies with45Ca2+ using scintillation counting indicated a linear relationship between external Ca2+ concentration and Ca2+ uptake. Uptake of Ca2+ was enhanced in the presence of the ionophore while RR caused little inhibition.45Ca2+ uptake was only partially inhibited by RR when cells were subjected to a Ca2+, ionophore and RR mixture. Grain counts from light microscope autoradiographs after treatment of cells with45Ca2+/ionophore,45Ca2+/RR or45Ca2+ alone showed heavy, light and intermediate labelling respectively. In all instances the grains were evenly distributed within the cell. These observations are interpreted as supporting the suggestion that the ionophore enhances both the uptake of extracellular Ca2+ and release of Ca2+from an internal source, while the RR could only partially prevent movement of Ca2+ through the plasma mebrane. A model is presented suggesting that tentacle retraction is mediated by cytosolic Ca2+ levels which are determined by the fluxing of Ca2+ across the plasma membrane and the membrane of elongate dense bodies which act as internal Ca2+ reservoirs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279445
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  • 6
    Electronic Resource
    Electronic Resource
    Magnitude and modulation of pancreatic β-cell gap junction electrical conductance in situ (1995)
    Springer
    The journal of membrane biology 146 (1995), S. 163-176 
    Details
    ISSN: 1432-1424
    Keywords: Pancreatic islet ; Cell-to-cell coupling ; Calcium ; Burst ; Synchrony ; Insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The parallel gap junction electrical conductance between a β-cell and its nearest neighbors was measured by using an intracellular microelectrode to clamp the voltage of a β-cell within a bursting islet of Langerhans. The holding current records consisted of bursts of inward current due to the synchronized oscillations in membrane potential of the surrounding cells. The membrane potential record of the impaled cell, obtained in current clamp mode, was used to estimate the behavior of the surrounding cells during voltage clamp, and the coupling conductance was calculated by dividing the magnitude of the current bursts by that of the voltage bursts. The histogram of coupling conductance magnitude from 26 cells was bimodal with peaks at 2.5 and 3.5 nS, indicating heterogeneity in extent of electrical communication within the islet of Langerhans. Gap junction conductance reversibly decreased when the temperature was lowered from 37 to 30°C and when the extracellular calcium concentration was raised from 2.56 to 7.56 mm. The coupling conductance decreased slightly during the active phase of the burst. Activation of adenylate cyclase with forskolin (10 μm) resulted in an increase in cell-to-cell electrical coupling. We conclude that β-cell gap junction conductance can be measured in situ under near physiological conditions. Furthermore, the magnitude and physiological regulation of β-cell gap junction conductance suggest that intercellular electrical communication plays an important role in the function of the endocrine pancreas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238006
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  • 7
    Electronic Resource
    Electronic Resource
    Blue light but not red light induces a calcium transient in the moss Physcomitrella patens (Hedw.) B., S. & G. (1998)
    Springer
    Planta 206 (1998), S. 278-283 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Aequorin ; Blue light ; Calcium ; Moss ; Photomorphogenesis ; Physcomitrella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. In caulonemal filaments of the moss, Physcomitrella patens, which had been incubated in darkness, 3 s irradiation with blue light (λmax 450 nm) at fluence rates of 100 μmol m−2 s−1 and above caused a transient␣increase in cytosolic calcium ion concentration, [Ca2+]cyt, which was both intensity- and time-dependent. Measurements of [Ca2+]cyt were made using moss transformed with the cDNA for apoaequorin and reconstituting the Ca2+-dependent photoprotein aequorin in the cytosol by incubation in coelenterazine.␣In response to blue light at fluence rates of 100–1000 μmol photons m−2 s−1, [Ca2+]cyt increased transiently from a basal level of approximately 50 nM to between 200 and 700 nM. Irradiation with red light did not evoke any measurable change in [Ca2+]cyt. The presence of calcium in the incubating medium was not required for the increase in [Ca2+]cyt to occur. A mutant strain, gad-139, was identified which required an irradiance of only 1 s to evoke a response. The kinetics showed a delay of approximately 6 s from the beginning of illumination before the beginning of the increase in [Ca2+]cyt. The data suggest that the activation of a photoreceptor rather than the direct opening of calcium channels is involved in this blue-light response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050401
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  • 8
    Electronic Resource
    Electronic Resource
    Calcium distribution in fertile and sterile anthers of a photoperiod-sensitive genic male-sterile rice (1998)
    Springer
    Planta 204 (1998), S. 183-192 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Anther ; Calcium ; Male sterility ; Oryza (fertility) ; Pollen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Potassium antimonate was used to locate Ca2+ in fertile and sterile anthers of a photoperiod-sensitive genic male-sterile rice (Oryza sativa L. japonica). During the development of fertile anthers, abundant calcium precipitates accumulated in the anther walls and on the surface of pollen grains and Ubish bodies at the late developmental stage of the microspore, but not in the cytoplasm of pollen grains. Following the accumulation of starch grains in pollen, calcium precipitates on pollen walls diminished and increased in parenchymatous cells of the connective tissue. In sterile anthers, calcium precipitates were abundant in the middle layer and endothecium, but not in the tapetum, as was found in fertile anthers. A special cell wall was observed between the tapetum and middle layer of sterile anthers that appeared to relate to distinctive calcium accumulation patterns and poor pollen wall formation in the loculi. The formation of different patterns of antimonate-induced calcium precipitates in the anthers of photoperiod-sensitive genic male-sterile rice indicates that anomalies in the distribution of calcium accumulation correlate with the failure of pollen development and pollen abortion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050245
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of pyrophosphate and diphosphonates on the dissolution of hydroxyapatites using a flow system (1980)
    Springer
    Calcified tissue international 31 (1980), S. 153-159 
    Details
    ISSN: 1432-0827
    Keywords: Hydroxyapatite ; Dissolution ; Pyrophosphate, Diphosphonates ; Calcium ; Phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02407176
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  • 10
    Electronic Resource
    Electronic Resource
    Effects of 1α-hydroxy vitamin D3 on the rachitic chick intestine: A comparison to the effects of 1,25-dihydroxyvitamin D3 (1980)
    Springer
    Calcified tissue international 32 (1980), S. 9-17 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02408517
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