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  • Calcium
  • Springer  (199)
  • American Institute of Physics (AIP)
  • Blackwell Publishing Ltd
  • 1990-1994  (101)
  • 1980-1984  (98)
  • 1955-1959
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  • 1
    Electronic Resource
    Electronic Resource
    Veratridine triggers exocytosis in Paramecium cells by activating somatic Ca channels (1994)
    Springer
    The journal of membrane biology 142 (1994), S. 229-240 
    Details
    ISSN: 1432-1424
    Keywords: Calcium ; Exocytosis ; Membrane fusion ; Paramecium tetraurelia ; Veratridine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Paramecium tetraurelia wild-type (7S) cells respond to 2.5 mm veratridine by immediate trichocyst exocytosis, provided [Ca2+] o (extracellular Ca2+ concentration) is between about 10−4 to 10−3 m as in the culture medium. Exocytosis was analyzed by light scattering, light and electron microscopy following quenched-flow/ freeze-fracture analysis. Defined time-dependent stages occurred, i.e., from focal (10 nm) membrane fusion to resealing, all within 1 sec. Veratridine triggers exocytosis also with deciliated 7S cells and with pawn mutants (without functional ciliary Ca channels). Both chelation of Ca2+ o or increasing [Ca2+] o to 10−2 m inhibit exocytotic membrane fusion. Veratridine does not release Ca2+ from isolated storage compartments and it is inefficient when microinjected. Substitution of Na+ o for N-methylglucamine does not inhibit the trigger effect of veratridine which also cannot be mimicked by aconitine or batrachotoxin. We conclude that, in Paramecium cells, veratridine activates Ca channels (sensitive to high [Ca2+] o ) in the somatic, i.e., nonciliary cell membrane and that a Ca2+ influx triggers exocytotic membrane fusion. The type of Ca channels involved remains to be established.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234945
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  • 2
    Electronic Resource
    Electronic Resource
    Triton channels are sensitive to divalent cations and protons (1994)
    Springer
    The journal of membrane biology 141 (1994), S. 83-90 
    Details
    ISSN: 1432-1424
    Keywords: Phospholipid bilayers ; Triton X-100 ; Ion channels ; Calcium ; Zinc ; Protons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Addition of Triton X-100 to planar bilayers composed of dioleoyl phosphatidyl choline, diphytanoyl phosphatidyl choline or mono-oleoyl glycerol induces single channel-like events when electrical conductivity across the bilayer is measured. Addition of divalent cations or protons causes channels to disappear; single channel conductance of remaining channels is not significantly altered; addition of EDTA or alkali (respectively) reverses the effect. It is concluded that sensitivity to divalent cations and protons need not be dependent on specific channel proteins or pore-forming toxins, but may be a feature of any aqueous pore across a lipid milieu.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232876
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  • 3
    Electronic Resource
    Electronic Resource
    Modeling degranulation with liposomes: Effect of lipid composition on membrane fusion (1994)
    Springer
    The journal of membrane biology 141 (1994), S. 139-148 
    Details
    ISSN: 1432-1424
    Keywords: Calcium ; Cholesterol ; Liposomes ; Membrane fusion ; Phosphatidic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Degranulation involves the regulated fusion of granule membrane with plasma membrane. To study the role of lipid composition in degranulation, large unilamellar vesicles (LUVs) of increasing complexity in lipid compositions were constructed and tested for Ca2+-mediated lipid and contents mixing. Lipid-mixing rates of LUVs composed of phosphatidylethanolamine (PE) and phosphatidylserine (PS) were strongly decreased by the addition of either phosphatidylcholine (PC) or sphingomyelin (SM), while phosphatidylinositol (PI) had little effect. “Complex” LUVs of PC∶PE∶SM∶PI∶PS (24∶27∶20∶16∶13, designed to emulate neutrophil plasma membranes) also showed very low rates of both lipid mixing and contents mixing. The addition of cholesterol significantly lowered the Ca2+ threshold for contents mixing and increased the maximum rates of both lipid and contents mixing in a dose-dependent manner. Membrane remodeling, which occurs in neutrophil plasma membranes upon stimulation, was simulated by incorporating low levels of phosphatidic acid (PA) or a diacylglycerol (DAG) into complex LUVs containing 50% cholesterol. The addition of PA both lowered the Ca2+ threshold and increased the rate of contents mixing in a dose-dependent manner, while the DAG had no significant effect. The interaction of dissimilar LUVs was also examined. Contents-mixing rates of LUVs of two different cholesterol contents were intermediate between the rates observed for the LUVs of identical composition. Thus, cholesterol needed to be present in only one fusing partner to enhance fusion. However, for PA to stimulate fusion, it had to be present in both sets of LUVs. These results suggest that the rate of degranulation may be increased by a rise in the cholesterol level of either the inner face of the plasma membrane or the outer face of the granule membrane. Further, the production of PA can promote fusion, and hence degranulation, whereas the subsequent conversion of PA to DAG may reverse this promotional effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238247
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  • 4
    Electronic Resource
    Electronic Resource
    A novel Cl− conductance in cultured chick cardiac myocytes: Role of intracellular Ca2+ and cAMP (1994)
    Springer
    The journal of membrane biology 141 (1994), S. 59-68 
    Details
    ISSN: 1432-1424
    Keywords: Chloride conductance ; cAMP ; Calcium ; Ion Channel ; Cardiac Myocytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Cl− conductance in cultured embryonic chick cardiac myocytes was characterized using whole-cell patch clamp techniques. Following elimination of cation currents in Na+and K+-free internal and external solutions, the basal whole-cell current was predominantly a Cl− current. Cl−-sensitive current (I Cl) was defined as the difference between the whole-cell currents recorded in normal and low [Cl−] o when measured in the same cell. The whole-cell current in the absence or presence of 10 μm cAMP was time independent, displayed outward rectification with the pipette [Cl−] 〈 40 mm, and was not saturated with a physiological Cl− gradient. The Cl− current was also activated by 1 μm forskolin and inhibited by 0.3 mm anthracene-9-carboxylic acid (9-AC). Forskolin was less effective than cAMP (internal dialysis) in activating the Cl− current. The cAMP- or forskolin-activated and basal Cl− current were reasonably fit by the Goldman-Hodgkin-Katz equation. The calculated P Cl in the presence of cAMP was increased by fiveto sixfold over the basal level. In the presence of 5 mm EGTA to decrease free [Ca2+] i , the whole-cell current could not be stimulated by cAMP, forskolin or IBMX (0.1 mm). These data suggest that cultured chick cardiac myocytes have a low basal Cl− conductance, which, as in some mammalian cardiac ventricular myocytes, can be activated by cAMP. However, this study shows that the activation process requires physiological free [Ca2+] i . This study was supported by grants from the National Institutes of Health (HL-17670, HL-27105 and HL-07107) for M.L. and by Institutional funds of the University of Arkansas for Medical Sciences for S.L.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232874
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  • 5
    Electronic Resource
    Electronic Resource
    Regulation of electrical coupling between Arabidopsis root hairs (1994)
    Springer
    Planta 193 (1994), S. 67-73 
    Details
    ISSN: 1432-2048
    Keywords: Arabidopsis (root hairs) ; Calcium ; Electrical coupling of cells (pH, voltage) ; Inositol trisphosphate ; Plasmodesma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Voltage clamp was used to measure the voltage dependence of cell-to-cell coupling via plasmodesmata between higher-plant cells (root hairs of Arabidopsis thaliana (L.) Heynh.). In addition, ionophoresis was used to introduce a variety of ions [Ca2+, inositol-trisphosphate, Li+, K+, Mg2+, ethylene glycol-bis(β-aminoethyl ether)-N,N,N′, N′-tetraacetic acid (EGTA), 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA), H+, and OH−] to examine whether they regulate cell-to-cell coupling. Electrical coupling showed high variability in this single cell type at the same developmental stage; the coupling ratio ranged from near 0% to about 90% with a mean value of 32%. It was voltage independent for intracellular voltage gradients (transplasmodesmatal) of -163 to 212 mV. While Ca2+ closes the plasmodesmatal connections (at concentrations higher than those causing cessation of cytoplasmic streaming), inositol-trisphosphate and lithium are without effect. Apparently, inositol-trisphosphate may not cause increased cytosolic Ca2+ in root hairs. Alkalinization by OH ionophoresis caused a modest decline in cell-to-cell coupling, as did acidification by H+ ionophoresis (to an extent causing the cell to become flacid). Increases in cytosolic K+, Mg2+, and the calcium chelator BAPTA by ionophoresis had no effect on cell-to-cell coupling. The regulation (and lack thereof) reported here for plant plasmodesmata is quite similar to that of gap junctions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00191608
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  • 6
    Electronic Resource
    Electronic Resource
    Spatial distribution of solutes, K, Na, Ca and their deposition rates in the growth zone of primary cotton roots: Effects of NaCl and CaCl2 (1994)
    Springer
    Planta 194 (1994), S. 34-41 
    Details
    ISSN: 1432-2048
    Keywords: Calcium ; Gossypium (root, solutes) ; Root ; Salinity ; Stress ; Solute ; Deposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cotton (Gossypium hirsutum L. cv. Acala SJ-2) seedlings were grown in modified Hoagland nutrient solution with or without 150 mM NaCl and supplemental 10 mM CaCl2. The spatial distribution of bulk-tissue osmotic potential (ΨS) and total osmotica, K, Na and Ca contents were determined in the growth zone of the primary root. This information was combined with the growth-velocity data from an earlier study (Zhong and Läuchli 1993) to estimate net deposition rates of osmoticum, water, K, Na and Ca by using the continuity equation. The ΨS was essentially uniform along the growth region for all treatments and considerably lowered by 150 mM NaCl in the medium. Total osmotica deposition was well synchronized with growth and deposition rates were enhanced by 150 mM NaCl. Osmoregulation in the treatments with 150 mM NaCl was indicated by an apparent solute accumulation which appeared to be due to the enhancement of osmoticum deposition rates. The presence of 150 mM NaCl greatly reduced the deposition rates of K and Ca throughout the growth zone; 10 mM Ca mitigated this effect only on K deposition in the apical 2.5-mm region. The deposition rate of Na was increased greatly by 150 mM NaCl; the increase was reduced by 10 mM Ca. At 150 mM NaCl, selectivity of K versus Na of the root was enhanced greatly in the apical 2mm region by the presence of 10 mM Ca; this mitigating effect by Ca declined rapidly with distance from the root tip. We conclude that one possible mechanism by which supplemental Ca alleviates the inhibitory effects of NaCl on cotton root growth is by maintaining plasma-membrane selectivity of K over Na.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201032
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  • 7
    Electronic Resource
    Electronic Resource
    Calcium plays a central role in phase shifting the ocular circadian pacemaker of Aplysia (1994)
    Springer
    Journal of comparative physiology 175 (1994), S. 415-423 
    Details
    ISSN: 1432-1351
    Keywords: Aplysia ; Calcium ; Circadian ; Light ; Serotonin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The eye of the marine mollusk Aplysia californica contains an oscillator that drives a circadian rhythm of spontaneous compound action potentials in the optic nerve. Both light and serotonin are known to influence the phase of this ocular rhythm. The aim of the present study was to evaluate the role of extracellular calcium in both light and serotonin-mediated phase shifts. Low calcium treatments were found to cause phase shifts which resembled those produced by the transmitter serotonin. However, unlike serotonin, low calcium neither increased ocular cAMP levels nor could these phase shifts be prevented by increasing extracellular potassium concentration. Low calcium-induced phase shifts were prevented by the simultaneous application of the translational inhibitor anisomycin and low calcium treatment resulted in changes in [35S]methionine incorporation into several proteins as measured by a two-dimensional electrophoresis gel analysis. Finally, light treatments failed to produce phase shifts in the presence of low calcium or the calcium channel antagonist nickel chloride. These results are consistent with a model in which serotonin phase shifts the ocular pacemaker by decreasing a transmembrane calcium flux through membrane hyperpolarization while light-induced phase shifts are mediated by an increase in calcium flux.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00199249
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  • 8
    Electronic Resource
    Electronic Resource
    Growth hormone administration potentiates the effect of treadmill exercise on long bone formation but not on the vertebrae in middle-aged rats (1994)
    Springer
    Calcified tissue international 54 (1994), S. 38-43 
    Details
    ISSN: 1432-0827
    Keywords: Osteoporosis ; Bone remodeling ; Physical activity ; Aging ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract To determine whether growth hormone administration would potentiate bone response to the stimulation of exercise, 80 female rats aged 14 months were divided into control (CON), ovine growth hormone administration (0.5 mg/kg daily) (GH), treadmill exercise (17 m/minute, 60 minutes daily) (EX), and GH+EX groups for 9 and 16 weeks. Static and dynamic histomorphometry were measured on the tibial shaft and (L-5) vertebral cortical bone. The periosteal and endocortical bone formation rate of the tibial shaft were higher in both EX and GH+EX than in the CON group in the 9-week study. There is a synergistic interaction between the two interventions in both cortical surfaces. After 16 weeks of study, the cortical bone area and periosteal bone formation rate were higher only in the EX than in the CON group. In the L-5 vertebra, the labeled surface on the periosteum was higher in the EX and the bone formation rate on the endocortical surface was higher in the GH than in the CON group. However, there was a negative interaction when the two interventions were combined. We conclude that a low-dose of growth hormone administration could initially potentiate long bone response to exercise. However, from the present study, long-term treatment with low-dose growth hormone administration does not enhance the increase in bone mass from exercise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00316288
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  • 9
    Electronic Resource
    Electronic Resource
    Intact serum parathyroid hormone levels increase during running exercise in well-trained men (1994)
    Springer
    Calcified tissue international 54 (1994), S. 256-261 
    Details
    ISSN: 1432-0827
    Keywords: Calcium ; Lactate ; Acidosis ; Treadmill ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract The purpose of this study was to examine the influence of exercise on the serum concentrations of intact parathyroid hormone (PTH). Serum PTH and plasma lactate were measured in 15 well-trained men, 9 long-distance runners and 6 fire-fighters, during two running exercises. Test one consisted of 40-minute treadmill running with a stepwise increased load and test two consisted of 50-minute treadmill running with a constant velocity. When the load was step-wise increased, the PTH concentrations increased moderately at the slower running paces but reached a final value that was about 50% higher than the starting value. This rise occurred despite a concomitant increase of total serum calcium from 2.38±0.06 to 2.49±0.05 mmol/liter (P〈0.01). During the constant running exercise, the long-distance runners, but not the fire-fighters, displayed a significant increase in PTH concentrations although the rise in total serum calcium was similar in both groups. There was a weak correlation between the changes in PTH and lactate in both exercises. The findings demonstrate that both high and low intensity exercise enhance release of PTH in long-distance runners through a mechanism that does not involve serum calcium. This relationship might be of importance for bone mass in men performing long-distance training.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00295947
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  • 10
    Electronic Resource
    Electronic Resource
    Combined magnetic fields increased net calcium flux in bone cells (1994)
    Springer
    Calcified tissue international 55 (1994), S. 376-380 
    Details
    ISSN: 1432-0827
    Keywords: Electromagnetic ; Bone ; Calcium ; Osteoblast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Low energy electromagnetic fields (EMF) exhibit a large number of biological effects. A major issue to be determined is “What is the lowest threshold of detection in which cells can respond to an EMF?” In these studies we demonstrate that a low-amplitude combined magnetic field (CMF) which induces a maximum potential gradient of 10-5 V/m is capable of increasing net calcium flux in human osteoblast-like cells. The increase in net calcium flux was frequency dependent, with a peak in the 15.3–16.3 Hz range with an apparent bandwidth of approximately 1 Hz. A model that characterizes the thermal noise limit indicates that nonspherical cell shape, resonant type dynamics, and signal averaging may all play a role in the transduction of lowamplitude EMF effects in biological systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00299318
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  • 11
    Electronic Resource
    Electronic Resource
    Effects of magnesium deficiency on strength, mass, and composition of rat femur (1994)
    Springer
    Calcified tissue international 54 (1994), S. 44-49 
    Details
    ISSN: 1432-0827
    Keywords: Bone ; Stress ; Elasticity ; Mechanical properties ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Magnesium (Mg) participates in the normal formation and remodeling of bone. However, little is known about effects of Mg status on the biomechanical function of bone. We examined gross morphometry and composition as well as biomechanical properties of the femurs of male rats fed diets adequate or deficient in Mg. Comparison of deficient animals and controls yielded a number of differences (all significant at P〈0.05). Mg-depleted animals exhibited slow growth, inefficient food utilization, and greatly reduced concentrations of Mg in both serum and femur ash. Compared with controls, femurs from depleted animals were shorter, but wet weights, diameters, and midfemoral cross-sectional areas showed no differences. Bone length was reduced to a greater degree than could be accounted for by differences in body weights between the groups. Bones of Mg-deficient rats contained less dry matter and less ash (which contained more Ca/g) than those of controls, along with a higher percentage of moisture. Significantly reduced bone strength in depleted animals was evident from the lighter loads supported at the elastic limit (yield point) and at fracture and from decreased stresses accompanying those loads. Modulus of elasticity, however, was not affected by Mg depletion. Different yield and breaking loads were related to different body weights of groups, but stresses were reduced for deficient bones even after adjusting for body size. Our data establish abnormal biomechanical behavior of cortical bone in Mg-deficient animals and emphasize the importance of measuring such functional properties of bone in the assessment of responses to altered metabolic conditions under experimental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00316289
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  • 12
    Electronic Resource
    Electronic Resource
    Chicken soup revisited: Calcium content of soup increases with duration of cooking (1994)
    Springer
    Calcified tissue international 54 (1994), S. 486-488 
    Details
    ISSN: 1432-0827
    Keywords: Calcium ; Duration of cooking ; Soup
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Because low dietary calcium intake may accelerate bone loss, patients often are advised to increase their dietary intake of calcium. However, some patients may be unable to tolerate good calcium sources such as dairy products. We postulated that the calcium content of soups and stews could be increased by prolonged cooking with a beef bone. Three experiments were done to prove this theory: (1) a bone soup made with a beef bone and distilled water, cooked for 24 hours; (2) a bone-vegetable soup cooked the same way; and (3) a vegetable soup made the same way but without the bone. It was concluded that prolonged cooking of a bone in soup increases the calcium content of the soup when cooked at an acidic, but not at a neutral pH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00334329
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  • 13
    Electronic Resource
    Electronic Resource
    Calcium currents in osteoblastic cells: Dependence upon cellular growth stage (1994)
    Springer
    Calcified tissue international 55 (1994), S. 128-133 
    Details
    ISSN: 1432-0827
    Keywords: Osteoblast ; Plasma membrane ; Calcium ; Ion channel ; Cell proliferation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Patch clamp physiological techniques were used to characterize the voltage-activated calcium currents (VACC) expressed in the plasma membrane of osteoblastic cells as a function of time in culture and proliferative state of the cell. Osteoblast-enriched preparations were isolated by collagenase digestions of newborn rat calvaria and cultured under different conditions which affected cell proliferation (i.e., low serum in the media to arrest proliferation). VACC were isolated by replacing the intracellular potassium with cesium, and adding 1 μM tetrodotoxin to the bath. Under conditions that favored cell proliferation, low cell density, and media supplemented with 10% fetal calf serum (FCS), a transient calcium current was not expressed until day 3 in culture. There was a statistically significant relationship between the precentage of cells expressing this current and the time in culture. The magnitude of the current significantly increased as days in culture increased. Under the same conditions, the sustained VACC was detected after 7 or 8 days in culture. However, arresting cell proliferation after 2 days in culture by reducing the FCS concentration to 0.01% induced the expression of the sustained VACC the next day. The data suggest that the expression of VACC in the plasma membrane of rat calvarial osteoblasts depends on the time in culture and the state of proliferation of the cells. These results should prove to be valuable in studying the functional significance of VACC in osteoblastic cells and their regulation by various bone regulatory agents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00297188
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  • 14
    Electronic Resource
    Electronic Resource
    Nocturnal rise in markers of bone resorption is not abolished by bedtime calcium or calcitonin (1994)
    Springer
    Calcified tissue international 55 (1994), S. 349-352 
    Details
    ISSN: 1432-0827
    Keywords: Pyridinolines ; Type I collagen carboxyterminal telopeptide ; Osteoporosis ; Calcium ; Calcitonin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract As assessed by urine pyridinium cross-links, bone resorption increases at night. This has been ascribed to either the nocturnal rise of serum parathyroid hormone (PTH) or immobilization. ICTP is the carboxyterminal telopeptide region of type I collagen in bone, cross-linked via pyridinium cross-links and liberated during the degradation of type I collagen. To study whether the nocturnal rise in bone resorption is seen also in serum type I collagen carboxyterminal telopeptide (ICTP) and whether this rise is abolished by bedtime calcium or calcitonin, nine healthy postmenopausal women participated in three 24 hour sessions. At 2200 hours, either 1 g of oral calcium or 200 IU of intranasal calcitonin or no treatment (control session) were given. The participants were recumbent from 2200 hours to 0600 hours. Like urinary pyridinolines, serum ICTP showed a clearcut nocturnal rise during the control session, increasing from 3.7±0.3 μg/liter (mean±SE) at 2000 hours to 4.9±0.4 μg/liter at 0600 hours (P〈0.001). Administration of calcium did not affect either serum ICTP or urinary pyridinolines, although it decreased serum intact PTH by 18% (P〈0.001) as assessed by areas under curve (AUC) after 2200 hours. Serum ICTP and urinary pyridinolines remained unchanged also after administration of calcitonin which increased the AUC for serum intact PTH by 9% (P〈0.05). In conclusion, serum ICTP follows a circadian rhythm in healthy postmenopausal women. The nocturnal rise in markers of bone resorption is not due to PTH, and its dependency on the function of osteoclasts is open to question.
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    URL: http://dx.doi.org/10.1007/BF00299313
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  • 15
    Electronic Resource
    Electronic Resource
    Calcification of the human thoracic aorta during aging (1994)
    Springer
    Calcified tissue international 54 (1994), S. 268-273 
    Details
    ISSN: 1432-0827
    Keywords: Aging ; Aorta ; Calcium ; Elastin ; Arteriosclerosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract The rate of calcification within the human thoracic aorta from completion of body growth to advanced old age was examined. Fifty-eight aortae, obtained at necropsy, were dissected into four layers: the complete intima and the separated media, which was subdivided into three tissue samples of equal thickness, defined as the media-inner,-middle, and-outer layers. The sampling sites selected for analysis were from regions of the aortic surface that were free of atherosclerotic plaques. The calcium content within each tissue layer of the aorta was determined. Arterial wall thickness and the cholesterol content of the four layers were also measured. Intimal calcification increased progressively during aging: from 1.6 μg Ca/mg tissue at 20 years of age to 5.2 μg Ca/mg tissue by 90 years of age. When intima calcium concentration was expressed by tissue volume (w/v), no significant change during aging was found. Medical calcification, as w/v and by w/w, increased throughout aging. Calcium accumulation was most marked in the middle, elastin-rich layer of the media, increasing from 1.4 μg Ca/mg tissue at 20 years of age to 49.50 μg Ca/mg tissue by 90 years of age. Calcium levels also increased in the other media layers, but at a slower rate then that found within the middle media.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00295949
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  • 16
    Electronic Resource
    Electronic Resource
    Human recombinant interleukin-1 receptor antagonist blocks bone resorption induced by interleukin-1β but not interleukin-1α (1994)
    Springer
    Calcified tissue international 55 (1994), S. 12-15 
    Details
    ISSN: 1432-0827
    Keywords: IL-1α ; IL-1β ; IL-1 receptor antagonist ; Bone ; Calcium ; Parathyroid hormone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Both interleukin-1α (IL-1α) and interleukin-1β (IL-1β) are powerful stimulators of bone resorption in vivo and in vitro. Interleukin-1 receptor antagonist (IL-1ra) binds to many interleukin-1 receptors. It does not activate the receptor and effectively blocks the action of IL-1α and IL-1β. In this study, human recombinant IL-1ra, at 100-fold excess, was found to block bone resorption in cultured mouse calvaria due to IL-1β but not IL-1α. These observations may be explained by differential affinities of receptors for IL-1α, IL-1β and rhIL-1ra on target bone cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310162
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  • 17
    Electronic Resource
    Electronic Resource
    Islet amyloid polypeptide (amylin) increases the renal excretion of calcium in the conscious dog (1994)
    Springer
    Calcified tissue international 55 (1994), S. 269-273 
    Details
    ISSN: 1432-0827
    Keywords: Islet amyloid polypeptide ; Amylin ; Calcium ; Urine ; Parathyroid hormone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Islet amyloid polypeptide (IAPP) is a member of the calcitonin/CGRP family and has been isolated from the β-cell of pancreatic islets. Recent evidence suggests that this peptide may be involved in calcium metabolism in that its administration resulted in lowering of serum calcium levels. To determine the mechanism of IAPP-induced hypocalcemia, the peptide was infused at 50 pmol/min/kg for 90 minutes in conscious male mongrel dogs. Infusion of the peptide resulted in a modest decline in the total serum calcium concentration (10.4±0.2 to 9.4±0.2 mg/dl; P〈0.05) and a concomitant increase in urinary calcium excretion (3.6±0.6 to 6.9±2.0 mg/dl; P〈0.01). Based on an extracellular volume of 7 liter in a 28 kg dog, the total decrement in calcium due to IAPP was 41.3±2.4 mg, whereas the total increase in urinary calcium was 3.2±0.7 mg. There were no detectable changes in calcitonin. We conclude that IAPP lowers serum calcium and increases the renal excretion of calcium independently of calcitonin. However, the calciuria can only account for a small component of the hypocalcemic effect and therefore, an additional calcium lowering effect of IAPP exits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310405
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  • 18
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    Isolation and characterization of a calmodulin-like protein from the cyanobacterium Nostoc sp. PCC 6720 (1994)
    Springer
    Archives of microbiology 161 (1994), S. 352-358 
    Details
    ISSN: 1432-072X
    Keywords: Calcium ; binding protein ; Calmodulin ; Nostoc sp. PCC 6720
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A 21-kDa novel polypeptide which possesses characteristics normally considered to be diagnostic of the calmodulin present in eukaryotic cells was isolated from the cyanobacterium Nostoc sp. PCC 6720. The major technique employed in the isolation of the polypeptide was ion-exchange chromatography on a Mono Q column. The 21-kDa polypeptide was shown: to activate pea NAD kinase in vitro, in a Ca2+ requiring reaction; to react with polyclonal antibodies raised against spinach calmodulin, but not with those raised against bovine brain calmodulin; and to exhibit a Ca2+ dependent shift in migration during SDS-PAGE.
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    URL: http://dx.doi.org/10.1007/BF00303592
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    Some factors controlling carotene destruction by chloroplasts in vitro (1994)
    Springer
    Plant foods for human nutrition 45 (1994), S. 35-46 
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    ISSN: 1573-9104
    Keywords: Carotene ; Chloroplasts ; Leaf protein ; Alum ; Calcium ; Citrate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Loss of β carotene from moist leaf protein stored with a preservative, is closely simulated by the destruction of β carotene by acetone extracted chloroplasts (stroma) suspended in acetone containing 30% water. During this exposure, stroma lose destructive ability, but it is restored by mercaptoacetate and other reducing agents. Stroma can therefore be used repeatedly. This catalytic process is activated by removing intrinsic inhibitors, predominantly calcium, by extraction at pHs less than 4, or by alum. The objective is to find inhibitors which would be acceptable in a food. That restricts choice. Citrate, tartarate and phosphate are among the more attractive possibilities.
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    URL: http://dx.doi.org/10.1007/BF01091227
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    Role of calcium in the inhibition of nitrogenase activity by Methylparathion and Benthiocarb in the cyanobacterium Nostoc muscorum (1994)
    Springer
    World journal of microbiology and biotechnology 10 (1994), S. 303-307 
    Details
    ISSN: 1573-0972
    Keywords: Calcium ; cyanobacterium ; herbicide ; nitrogenase ; insecticide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Methylparathion and Benthiocarb inhibition of N2 fixation in the cyanobacterium Nostoc muscorum was reversed by Ca2+ at 1 mm but not at 0.1 mm. The concentration of intracellular Ca2+ was relatively high in the presence of these pesticides when 1 mm Ca2+ was also present, indicating that intracellular Ca2+ may participate in protecting nitrogenase activity against Methylparathion and Benthiocarb.
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    URL: http://dx.doi.org/10.1007/BF00414869
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  • 21
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    Polyanion-mediated mineralization — assembly and reorganization of acidic polysaccharides in the Golgi system of a coccolithophorid alga during mineral deposition (1994)
    Springer
    Protoplasma 177 (1994), S. 108-122 
    Details
    ISSN: 1615-6102
    Keywords: Algae ; Calcium ; Coccolithophorids ; Golgi ; Mineralization ; Polyanions ; Polysaccharides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Immunolocalization of two highly acidic polysaccharides (PS-1 and PS-2) in a calcifying algaPleurochrysis carterae is described throughout the mineralization process, from before crystal nucleation through the cessation of crystal growth. This unicellular coccolithophorid alga is a useful model for mineralization because it produces calcified scales known as coccoliths in homogeneous cell culture. PS-1 and PS-2 were localized in the crystal coats of mature coccoliths and in electron dense Golgi particles. The polyanions are synthesized in medial Golgi cisternae and co-aggregate with calcium ions into discrete 25 nm particles. Particle-laden vesicles bud from cisternal margins and fuse with a coccolith-forming saccule containing an organic oval-shaped scale which forms the base of the future coccolith. The particles are localized on the base before the onset of mineral deposition and are present in the coccolith saccule throughout the period of crystal (CaCO3) nucleation and growth. During the final phase of coccolith formation, the particles disappear, and the mature crystals acquire an amorphous coat containing PS-1 and PS-2 polysaccharides which remain with the mineral phase after the coccoliths are extruded from the cell. Postulated mechanisms of polyanion-mediated mineralization are reviewed and their relevance to the calcification of coccoliths is addressed.
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    URL: http://dx.doi.org/10.1007/BF01378985
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    Pharmacological changes associated with cardiac ischaemia (1994)
    Springer
    Pharmacy world & science 16 (1994), S. 34-35 
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    ISSN: 1573-739X
    Keywords: Calcium ; Chronotropic response ; Inotropic response ; Ischemia ; Receptors, adrenergic ; Receptors, muscarinic ; Signal transduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870939
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    Distribution of the anionic sites in the cell wall of apple fruit after calcium treatment (1994)
    Springer
    Protoplasma 178 (1994), S. 156-167 
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    ISSN: 1615-6102
    Keywords: Calcium ; Cationic gold ; Cell wall ; Fruit ; Pectin ; Ripening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ripening and softening of fleshy fruits involves biochemical changes in the cell wall. These changes reduce cell wall strength and lead to cell separation and the formation of intercellular spaces. Calcium, a constituent of the cell wall, plays an important role in interacting with pectic acid polymers to form cross-bridges that influence cell wall strength. In the present study, cationic colloidal gold was used for light and electron microscopic examinations to determine whether the frequency and distribution of anionic binding sites in the walls of parenchyma cells in the apple were influenced by calcium, which was pressure infiltrated into mature fruits. Controls were designed to determine the specificity of this method for in muro labelling of the anionic sites on the pectin polymers. The results indicate that two areas of the cell wall were transformed by the calcium treatment: the primary cell walls on either side of the middle lamella and the middle lamella intersects that delineate the intercellular spaces. The data suggest that calcium ions reduce fruit softening by strengthening the cell walls, thereby preventing cell separation that results in formation of intercellular spaces.
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    URL: http://dx.doi.org/10.1007/BF01545965
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    Triggered exocytosis and endocytosis have different requirements for calcium and nucleotides in permeabilized bovine chromaffin cells (1993)
    Springer
    The journal of membrane biology 134 (1993), S. 1-13 
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    ISSN: 1432-1424
    Keywords: Endocytosis ; Exocytosis ; Calcium ; Adrenal medulla
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The intracellular requirements for membrane recapture in permeabilized chromaffin cells were compared to the requirements for exocytosis from the same cells. In permeabilized bovine chromaffin cells, calcium-driven exocytosis also triggers, with a short delay, uptake of extracellular horseradish peroxidase (HRP). This internalized HRP remains compartmentalized within the cell and migrates to a low density band on a Percoll gradient which is distinct from the heavier chromaffin granules. The amount of horseradish peroxidase internalized is similar in intact and leaky cells and is approximately equivalent to the volumes secreted. Endocytosis in both preparations is blocked by botulinum toxin, operates in a collapsed membrane potential, and is inhibited by low temperature. In permeabilized cells, exocytosis and coupled endocytosis are activated by the same concentrations of Ca2+ and MgATP. Although secretion requires Ca2+ and MgATP, once exocytosis has occurred the subsequent endocytosis can proceed in the virtual absence of Ca2+ or MgATP, and is largely unaffected by a variety of nucleotide triphosphates (including nonhydrolyzable analogues), and cyclic nucleotides. These data suggest that endocytosis can proceed, once exocytosis has been triggered, under conditions that are quite different from those necessary to support exocytosis, and that the specific requirements for Ca2+ and MgATP in secretion are for the exocytotic limb of the secretory cycle rather than for the associated endocytotic pathway.
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    Deposition of BaSO4 in the tight junctions of amphibian epithelia causes their opening; apical Ca2+ reverses this effect (1993)
    Springer
    The journal of membrane biology 134 (1993), S. 15-29 
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    ISSN: 1432-1424
    Keywords: Amphibian skin ; Amphibian urinary bladder ; Tight junction ; Paracellular path ; Calcium ; Barium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Selective deposition of BaSO4 in the tight junctions (TJs) of frog skins led to profound and reversible functional alterations of these structures, as revealed by changes of tissue conductance (G), clamping current (I), and fluxes of extracellular markers (sulfate (JSO 4) and sucrose (JSUC)). Experiments were performed with nominally Ca2+ -free simple salt solutions on the apical side (usually KCl) and Na2SO4-Ringer on the inner side of skins. The deposition of BaSO4 in the TJs was obtained by diffusion and/or migration through the paracellular path of Ba2+ from the apical solution and SO 4 2− from the inner solution. A brief presence (2 to 6 min) of apical Ba2+ (Ba2+ pulse) is followed (i.e., when Ba2+ is removed from the apical fluid) by a large increase of G, I, JSO 4 and JSUC, above pre-Ba2+ levels. These attain a steady state within 15 to 30 min (overshoot phase), characterizing a conspicuous increase of the paracellular permeability. During the overshoot phase, a second Ba2+ pulse blocks the paracellular route while apical Ba2+ is present, leading to a new and larger overshoot when the Ba2+ pulse is terminated. Addition of apical Ca2+ triggers the resealing of the TJs, resulting in a full recovery of G, I, JSO 4 and JSUC. This Ca2+ -induced recovery persists when apical Ca2+ is removed. The presence of a normal Ca2+ concentration in the inner bathing Ringer does not induce the recovery process. Tissues remain viable after being submitted to the Ba2+ treatment and the subsequent overshoot. Experiments performed in the urinary bladder of Rana catesbeiana and skins and urinary bladders of Bufo marinus indicate that Ba2+ effect can also be elicited in these tissues. The above results seem to report general properties of the TJs. Incidentally, they warn about the use of Ba2+ as an ion channel blocker in epithelial membranes in association with SO 4 2− -containing solutions on the contralateral side.
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    Ca2+ activation and pH dependence of a maxi K+ channel from rabbit distal colon epithelium (1993)
    Springer
    The journal of membrane biology 136 (1993), S. 9-21 
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    ISSN: 1432-1424
    Keywords: Maxi K+ channel ; Calcium ; pH ; Charybdotoxin ; Rabbit distal colon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract To determine if their properties are consistent with a role in regulation of transepithelial transport, Ca2+-activated K+ channels from the basolateral plasma membrane of the surface cells in the distal colon have been characterized by single channel analysis after fusion of vesicles with planar lipid bilayers. A Ca2+-activated K+ channel with a single channel conductance of 275 pS was predominant. The sensitivity to Ca2+ was strongly dependent on the membrane potential and on the pH. At a neutral pH, the K 0.5 for Ca2+ was raised from 20nm at a potential of 0 mV to 300nm at −40 mV. A decrease in pH at the cytoplasmic face of the K+ channel reduced the Ca2+ sensitivity dramatically. A loss of the high sensitivity to Ca2+ was also observed after incubation with MgCl2, possibly a result of dephosphorylation of the channels by endogenous phosphatases. Modification of the channel protein may thus explain the variation in Ca2+ sensitivity between studies on K+ channels from the same tissue. High affinity inhibition (K 0.5=10nm) by charybdotoxin of the Ca2+-activated K+ channel from the extracellular face could be lifted by an outward flux of K+ through the channel. However, at the ion gradients and potentials found in the intact epithelium, charybdotoxin should be a useful tool for examination of the role of maxi K+ channels. The high sensitivity for Ca2+ and the properties of the activator site are in agreement with an important regulatory role for the high conductance K+ channel in the epithelial cells.
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    The effects of calcium deficiency on Cucurbita pepo L. hypocotyl cells: A 31P nuclear-magnetic-resonance study (1993)
    Springer
    Planta 189 (1993), S. 306-311 
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    ISSN: 1432-2048
    Keywords: Auxin ; Calcium ; Cucurbita ; 31P nuclear magnetic resonance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Calcium deficiency in zucchini (Cucurbita pepo L.) is associated with reduced growth and a reduced ability to transport auxin (Allan and Rubery, 1991, Planta 183, 604–612). An investigation of the effects of calcium-deficiency on zucchini hypocotyl cells was made using weak-acid uptake and 31P-nuclear-magneticresonance (31P-NMR) spectroscopy in vivo and in tissue extracts. Calcium-deficient tissue had the same cytoplasmic and vacuolar pHs as normal tissue when extracellular pH was near neutral. At acidic external pH the vacuolar pH was lower in deficient tissue. Adenine nucleotides were present predominantly as ATP in both control and calcium-deficient tissues. Addition of calcium to calcium-deficient tissue, under conditions which cause recovery of auxin transport induced no changes in the 31P-NMR spectra of deficient tissue. The content of mobile, phosphorylated metabolites was reduced in calcium-deficient tissue in comparison to control tissue. However, a substantial increase in the content of phosphorylcholine occurs in calcium-deficient tissues compared with controls; this may reflect changes in lipid turnover in calcium-stressed cells.
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    Proton efflux from oat coleoptile cells and exchange with wall calcium after IAA or fusicoccin treatment (1993)
    Springer
    Planta 189 (1993), S. 377-383 
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    ISSN: 1432-2048
    Keywords: Acid-growth ; Auxin ; Avena ; Calcium ; Fusicoccin ; Ion exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Elongation growth of plant cells occurs by stretching of cell walls under turgor pressure when intermolecular bonds in the walls are temporarily loosened. The acid-growth theory predicts that wall loosening is the result of wall acidification because treatments (including IAA and fusicoccin) that cause lowered wall pH cause elongation. However, conclusive evidence that IAA primarily reduces wall pH has been lacking. Calcium has been reported to stiffen the cell walls. We have used a microelectrode ion-flux measuring technique to observe directly, and non-invasively, the net fluxes of protons and calcium from split coleoptiles of oats (Avena sativa L.) in unbuffered solution. Normal net fluxes are 10 nmol · m−2 · s−1 proton efflux and zero calcium flux. The toxin fusicoccin (1 μM) causes immediate efflux from tissue not only of protons, but also of calcium, about 110 nmol · m−2 · s−1 in each case. The data fit the “weak acid Donnan Manning” model for ion exchange in the cell wall. Thus we associate the known “acid-growth” effect of fusicoccin with the displacement of calcium from the wall by exchange for protons extruded from the cytoplasm. Application of 10 μM IAA causes proton efflux to increase transiently by about 15 nmol · m−2 · s−1 with a lag of about 10 min. The calcium influx decreases immediately to an efflux of about 20 nmol · m−2 · s−1. It appears that auxin too causes an “acid-growth” effect, with extruded protons exchanging for calcium in the cell walls.
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    Influence of calcium on blue-light-induced chloroplast movement in Lemna trisulca L. (1993)
    Springer
    Planta 189 (1993), S. 491-498 
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    ISSN: 1432-2048
    Keywords: Blue light ; Calcium ; Calcium ionophore ; Chloroplast movement ; Lemna
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The presence of calcium is essential for chloroplast movement induced by blue light in Lemna trisulca L. The regulatory role of calcium was confirmed by the inhibition of chloroplast movement by cytochalasin B and trifluoperazine. The calcium concentration in tissues was modified by ethylene glycol-bis(2-aminoethylether)-N,N,N′, N′-tetraacetic acid (EGTA), the calcium ionophore A23187 and La3+. Only a long period of incubation (12h) in EGTA or La3+ caused distrubances in chloroplast movement. This indicates that calcium influx is not essential for chloroplast movement. Those conditions that dramatically changed the internal calcium concentration, either applications of calcium ionophore A23187 and EGTA, or ionophore and La3+, markedly decreased the amplitude of response to blue-light pulses. This demonstrates that disturbances of chloroplast movement are observable only when internal stores of calcium are affected by Ca2+-antagonists. We suggest that the calcium involved in blue-light-induced chloroplast movement is derived from intracellular stores. The addition of Mg2+ to EGTA buffer counteracted its effect, indicating that Mg2+, as well as Ca2+, might possibly be involved in chloroplast movement.
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    Combined treatment with calcitonin and 1,25-dihydroxyvitamin D3 for osteoporosis in women (1993)
    Springer
    Calcified tissue international 53 (1993), S. 26-28 
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    ISSN: 1432-0827
    Keywords: Calcitonin ; Calcitriol ; Calcium ; Densitometry ; Osteoporosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Twenty-two middle-aged women with severe osteoporosis were treated for 2 years with either 0.5 mg of synthetic human calcitonin subcutaneously three times per week combined with 0.5 μg of calcitriol and 0.5 g of calcium per day orally or calcium only. The treatment with calcitonin plus calcitriol (12 patients) resulted in a significantly increased calcium absorption rate. The mean values for serum phosphate did not change during the treatment period and the mean values did not differ between the treatment groups, but the serum calcium and urinary Ca/Cr ratio increased somewhat in the group given the combined treatment. There was no evidence that the combined treatment improved the bone density in this study. It is possible that calcitriol, instead of increasing the effect of calcitonin by suppression of the parathyroid, might have counteracted its effect by increasing the bone resorption.
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    Impaired duodenal response to short-term dietary calcium restriction in adolescent spontaneously hypertensive rats (1993)
    Springer
    Calcified tissue international 52 (1993), S. 310-317 
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    ISSN: 1432-0827
    Keywords: SHR-WKY rats ; Calcium ; Calcitriol ; Intestine ; Calbindin ; Alkaline phosphatase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary the response pattern of plasma calcitriol level and related intestinal adaptation to short-term moderate calcium (Ca) restriction was examined in adolescent male, spontaneously hypertensive rats (SHR) and normotensive WKY control rats. Twelve-week-old SHR and WKY fed a low (0.1%) Ca diet for 3, 6, or 12 days were compared with rats of either strain fed a normal (1.0%) Ca diet. Plasma calcitriol response was measured and duodenal adaptation to Ca restriction was investigated by evaluating active Ca transport, calbindin-D9K (CaBP9K) protein, CaBP9k mRNA, and alkaline phosphatase activity (ALP). Under the normal Ca diet, no significant difference between strains was observed for all five parameters. In response to the low Ca diet, the SHR and WKY showed a similar increase (nearly 50%) in plasma calcitrol, starting at day 3 of this diet. However, only the WKY displayed the expected duodenal adaptation: active Ca transport increased at day 6 and CaBP9K as well as ALP increased at day 3 of the low Ca diet. The stimulation of the latter three parameters was maintained until day 12 of Ca restriction. Moreover, CaBP9K mRNA was increased in WKY after 3 days of Ca restriction. In contrast, the SHR had either no or only a minor increase of duodenal parameters in response to Ca restriction. Finally, a significant and positive correlation between Ca transport and plasma calcitriol and between Ca transport and CaBP9K was found in WKY but not in SHR. In conclusion, this study showed that the adolescent SHR was able to increase calcitriol production but unlike the WKY, it failed to fully adapt at the intestinal target level during a 12-day low Ca diet. Thus, our results provide further evidence for an impairment of the vitamin D endocrine system in adolescent SHR as demonstrated by an abnormal intestinal responsiveness to circulating calcitriol during moderate, short-term Ca restriction.
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    Plasma levels of parathyroid hormone, vitamin D, calcitonin, and calcium in association with endurance exercise (1993)
    Springer
    Calcified tissue international 52 (1993), S. 205-208 
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    ISSN: 1432-0827
    Keywords: Exercise ; Parathyroid hormone ; Vitamin D ; Calcitonin ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Nine male marathon runners were investigated during habitual training (week 0), after 3 weeks of training break (week 3), and after 2 weeks (week 5) and 4 weeks (week 7) of retraining. Maximal oxygen uptake, body fat (BF), and plasma levels of 25(OH)D3, 1,25(OH)2D3, parathyroid hormone (PTH), calcitonin (CT), albumin, and albumincorrected calcium were determined throughout weeks 0–7. The maximal oxygen uptake decreased after training break and increased during retraining (P=0.002). BF did not change significantly. Plasma 1,25(OH)2D3 was elevated after training break and decreased after 2 and 4 weeks of retraining [week 0: 44.0±3.7 (SEM) pg×1-1; week 3: 52.4±6.0 pg×1-1; week 5: 42.0±2.8 pg×1-1; week 7: 36.9±2.3 pg×1-1; P=0.03]. Plasma 25(OH)D3 did not change significantly. Plasma PTH increased throughout the training break and retraining (week 0: 1.36±0.25 pmol×1-1; week 3: 2.02±0.43 pmol×1-1; week 5: 2.23±0.60 pmol×1-1; week 7: 2.63±0.34 pmol×1-1; P=0.03). Albumincorrected calcium values were transiently decreased during retraining (week 3: 2.77±0.08 mM; week 5: 2.47±0.05 mM; week 7: 2.66±0.07 mM; P=0.01). Plasma CT did not change during training break, but was transiently decreased during retraining (week 0: 9.97±0.39 pmol×1-1; week 3: 9.91±0.37 pmol×1-1; week 5: 8.19±0.50 pmol×1-1; week 7: 9.02±0.45 pmol×1-1; P=0.01). Plasma CT was correlated to albumin (r=0.46, P=0.005), albumin-corrected calcium (r=0.34, P=0.04), and maximal oxygen uptake (r=0.45, P=0.006). Plasma 1,25(OH)2D3 was correlated to 25(OH)D3 (r=0.04, P=0.02), and BF (r=0.50, P=0.002). The described endurance training induced significant changes of plasma 1,25(OH)2D3 and PTH despite only transient changes of albumin-corrected calcium and CT.
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    Interleukin-1 receptor antagonist inhibits calcium accumulation in in vivo chronic granuloma induced by potassium permanganate (1993)
    Springer
    Calcified tissue international 52 (1993), S. 300-304 
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    ISSN: 1432-0827
    Keywords: Interleukin 1 ; Calcium ; Inflammation ; Granuloma ; Potassium permanganate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Interleukin-1 (IL-1) is a monokine that exerts multiple biological activity, including immunity and inflammation. Moreover, IL-1 is involved in Ca2+ release causing hypercalcemia and bone resorption. Recently, a 22 kDa natural inhibitor to IL-1 called interleukin-1 receptor antagonist (IL-1ra) has been described in human fluids, which specifically binds IL-1α or IL-1β receptors. In this study, we found that experimental granuloma induced by subcutaneous injections (0.2 ml) of potassium permanganate (KMnO4) 1:40 saturated crystal solution, after 7 days was strongly inhibited in size, weight and calcium content (measured as dry ash weight by incineration of granuloma tissue) compared with untreated controls, in mice treated intraperitoneally with IL-1ra (20 μg/bolus) given twice; the first at the same time of the induction of the granuloma and the second 24 hours later. In addition, leukotriene B4 and prostaglandin E2 were also inhibited in fresh granuloma of mice treated with IL-1ra. Taken together, these findings conclude for the first time, that the accumulation of calcium in chronic inflammatory states is strongly inhibited by IL-1ra, which decreases tissue calcergy and can potentially be useful for the treatment of calcium-related inflammatory diseases and malignancy-associated hypercalcemia.
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    The effects of liposome-encapsulated and free clodronate on the growth of macrophage-like cellsin vitro: The role of calcium and iron (1993)
    Springer
    Calcified tissue international 53 (1993), S. 139-146 
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    ISSN: 1432-0827
    Keywords: Clodronate ; Liposomes ; Macrophages ; Calcium ; Iron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Clodronate (dichloromethylene bisphosphonate) inhibits the activity of osteoclasts, thereby preventing bone resorption in disorders characterized by excessive bone loss. Intravenously injected clodronate encapsulated in liposomes is also known to inactivate phagocytic cells in spleen and liverin vivo. The macrophage suppressive effect of clodronate is of interest in autoimmune diseases, like rheumatoid arthritis, in which phagocytic cells are involved in inflammatory processes, but knowledge of the interaction of clodronate with phagocytic cells is scarce. We have studied the uptake of clodronate, both free and encapsulated in negatively charged liposomes, by the macrophage-like cell line RAW 264 and by other types of cell lines. The uptake was assessed by a growth inhibition assay. The liposome-encapsulated lodronate was 50 and 350 times more potent than free drug for RAW 264 and CVI-P, respectively. Cell lines with a lower endocytotic capacity were insensitive to liposome-mediated delivery of the drug. The action of free clodronate seemed to be extracellular in all cell lines studied. Calcium and/or iron have been suggested to be involved in the intracellular uptake and action of clodronate in phagocytic cells. We found that the uptake of free clodronate by RAW 264 cells was indeed mediated by calcium and iron, while the uptake of liposomal drugs was only slightly affected by calcium. The increased intracellular calcium concentration in macrophages did not significantly affect the growth-inhibitory properties of clodronate, whereas iron loading of the cells partially restored the cell growth. The data do not support the role of calcium chelation as a mechanism of action of clodronate, but suggest that intracellular iron is, at least partially involved.
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    Fluoride increases net45Ca uptake by SaOS-2 cells: The effect is phosphate dependent (1993)
    Springer
    Calcified tissue international 53 (1993), S. 187-192 
    Details
    ISSN: 1432-0827
    Keywords: Fluoride ; Osteosarcoma cells ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Previousin vitro studies have shown that the effect of fluoride to increase avian osteoblast-like cell proliferation was dependent on the phosphate concentration.In vitro studies have further revealed that fluoride could also have direct effects on osteoblast-like cells to increase phosphate uptake and transiently increase cytosolic calcium. The current studies were intended to determine whether fluoride could increase net45Ca uptake by human osteosarcoma (SaOS-2) cells and, if so, whether those effects would also be phosphate dependent. The results of these studies indicate that fluoride increased net45Ca uptake by SaOS-2 cells, with biphasic dose and time dependencies. After 30 minutes of exposure, net45Ca uptake was increased to a greater extent by 50 μM fluoride (217 ± 16% of control,P 〈 0.001) than by 200 μM fluoride; and the stimulatory effect of 100 μM fluoride on net45Ca uptake was greater after 20 minutes (187 ±22% of control,P 〈 0.001) than after 60 minutes (122 ± 7% of control,P 〈 0.05). These effects of fluoride to increase net45Ca uptake were dependent on the phosphate concentration in the medium. Fluoride had no effect on net45Ca uptake in medium containing 0.4 mM phosphate, but increased net45Ca uptake in medium containing 1.2 or 2.0 mM phosphate (P 〈 0.005). As the phosphate concentration was increased, the biphasic fluoride dose-response curve was shifted to a lower range of fluoride concentrations. These effects of fluoride were not unique to SaOS-2 cells with very high steady-state levels of skeletal alkaline phosphatase; similar effects were seen in a subpopulation of SaOS-2 cells with much lower alkaline phosphatase levels. Further studies indicated that the effects of fluoride to increase SaOS-2 cell proliferation and skeletal alkaline phosphatase activity showed a similar pattern of phosphate dependency. As the fluoride-dependent increases in3[H]-thymidine incorporation and net45Ca uptake were blocked by verapamil, these data are consistent with the general hypothesis that the osteogenic effects of fluoride are associated with acute effects to increase net Ca uptake.
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    URL: http://dx.doi.org/10.1007/BF01321836
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    Effect of changes in mineral composition and growth temperature on filament length and flagellation in the Archaeon Methanospirillum hungatei (1993)
    Springer
    Archives of microbiology 159 (1993), S. 512-520 
    Details
    ISSN: 1432-072X
    Keywords: Methanospirillum ; Morphology ; Flagella ; Archaea ; Growth conditions ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Methanospirillum hungatei strains GP1 and JF1 when cultivated at 37°C in JMA medium grew as motile single cells or short chains of cells (typically 10–30 μm long). When M. hungatei was grown in low Ca2+ concentrations or with the divalent cation chelator EDTA, the organism grew as long non-flagellated filaments (up to 900 μm long). The two strains had different thresholds of calcium concentrations for long filament formation (〈0.25 mM for GP1 and 〈0.15 mM for JF1) as well as different minimal Ca2+ requirements for growth. Both strains produced long, almost straight, filaments at Ca2+ concentrations near the minimum required for growth. At suboptimal growth temperatures the organisms still grew as short filaments but no longer possessed flagella. Western blot analysis indicated that flagellin monomer was present in cultures of long non-flagellated filaments and short non-flagellated cultures grown at suboptimal temperatures. The amount of flagellin present appeared to be equal in both non-flagellated and flagellated cultures. When cells were grown as long non-flagellated filaments and switched to growth conditions inducing short, flagellated forms, flagella were first observed at 2.5 h after this switch.
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    URL: http://dx.doi.org/10.1007/BF00249028
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    Purification, partial characterization, and subcellular localization of a 38 kilodalton, calcium-regulated protein of Rhizobium fredii USDA208 (1993)
    Springer
    Archives of microbiology 159 (1993), S. 250-256 
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    ISSN: 1432-072X
    Keywords: Calcium ; Nitrogen fixation ; Nodulation ; Periplasmic proteins ; Rhizobium fredii
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Calcium is essential for the growth of rhizobia and the formation of nitrogen-fixing root-nodules on legumes, but its precise role in these processes remains unknown. We have found that Rhizobium fredii USDA208 accumulates a major 38 kDa protein when grown in media supplemented with 0.3–2 μmM CaCl2. We have purified this protein and raised polyclonal antibodies against it. The protein initially is synthesized as a 40 kDa precursor which subsequently undergoes calcium-dependent processing to give rise to the mature polypeptide. Subcellular and immunocytochemical localization studies indicate that the 38 kDa protein accumulates preferentially in the periplasmic space. Its N-terminal sequence, AETIKIGVAGPMTG, shows significant homology to the N-termini of amino acid binding proteins from the periplasm, including leucine-, isoleucine-, and valine-specific binding proteins of Pseudomonas aeruginosa and Escherichia coli and a leucine-specific binding protein of E. coli. The R. fredii protein does not, however, bind [3H]-leucine. The 38 kDa protein is encoded by the bacterial chromosome. It is absent in several rhizobia other than R. fredii, but antigenically related polypeptides are present in Escherichia coli and Erwinia carotovora subsp. carotovora.
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    URL: http://dx.doi.org/10.1007/BF00248480
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    Amelioration of subsoil acidity in an Oxisol of the humid tropics (1993)
    Springer
    Biology and fertility of soils 15 (1993), S. 153-159 
    Details
    ISSN: 1432-0789
    Keywords: Calcium ; Maize ; Nitrogen ; Brazilian Amazon ; Cation leaching ; Canavalia ensiformes ; Mucuna aterrima
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary This work investigated the effectsof amendments of fertilizer N and lime on subsoil acidity and maize rooting depth in an acid soil of the central Amazon basin. A split-plot designed field experiment was conducted on a clayey Oxisol (Typic Acrudox) during a 16-month period. Main plots received 0 or 4 Mt ha-1 of lime. Subplots were four crop sequences: (1) Maize-green manure (Canavalia ensiformes); (2) maize-green manure (Mucuna aterrima); (3) maize-bare fallow, with the maize receiving 300 kg ha-1 of urea-N; and (4) bare fallow, with an application of 300 kg ha-1 of urea-N at the same time as sequence 3. Plots were periodically sampled to 1.2 m. The experimental site received 4265 mm of precipitation during 16 months; approximately 60%–90% of this rain percolated through the profile. Substantial amounts of Ca were leached from the 0–30 cm horizon during the experimental period, but only limited amounts accumulated in the subsoil. Base saturation below 45 cm was less than 50% at the end of the experiment regardless of lime treatment. Roots of maize were concentrated in the 0–30 cm layers in limed plots and the 0–20 cm layers in unlimed plots. In all treatments less than 5% of the roots was found below 50 cm. An acidity balance indicated that considerable acidity was leached below the plow layer and out of the profile.
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    URL: http://dx.doi.org/10.1007/BF00336435
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    Analysis of temperature dependence of cytoplasmic streaming using tonoplast-free cells of Characeae (1993)
    Springer
    Protoplasma 176 (1993), S. 174-177 
    Details
    ISSN: 1615-6102
    Keywords: Cytoplasmic streaming ; Nitellopsis ; Characeae ; Low temperature ; Actin ; Myosin ; Calcium ; pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The temperature dependence of cytoplasmic streaming in intact and tonoplast-free cells ofNitellopsis obtusa was studied using a cryomicroscope. The streaming velocity decreases linearly with decrease in the temperature in well-buffered tonoplast-free cells but non-linearly in some intact cells. These results suggest that low temperature causes a disturbance in the homeostasis of calcium and protons, which inhibit cytoplasmic streaming in intact cells.
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    URL: http://dx.doi.org/10.1007/BF01378954
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    Cessation of cytoplasmic streaming follows an increase of cytoplasmic Ca2+ during action potential inNitella (1993)
    Springer
    Protoplasma 174 (1993), S. 142-146 
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    ISSN: 1615-6102
    Keywords: Action potential ; Calcium ; Cytoplasmic streaming ; Nitella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Taking advantage of prolonged action potential under low temperature, we studied temporal relationship among the action potential, increase of cytoplasmic Ca2+ concentration and cessation of cytoplasmic streaming inNitella. The Ca2+ concentration began to increase at a very early stage of the action potential and the cessation of streaming followed that increase.
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    URL: http://dx.doi.org/10.1007/BF01379046
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    Membrane traffic from the endoplasmic reticulum to the Golgi apparatus is disturbed by an inhibitor of the Ca2+-ATPase in the ER (1993)
    Springer
    Protoplasma 177 (1993), S. 23-31 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Cyclopiazonic acid ; Endoplasmic reticulum ; Golgi apparatus ; Membrane traffic ; Secretory cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An electron microscopic study of cress (Lepidium sativum L.) roots treated with cyclopiazonic acid (CPA), an inhibitor of the Ca2+-ATPase in the endoplasmic reticulum (ER) has been carried out. Drastic changes in the endomembrane system of the secretory root cap cells were observed. After treatment with CPA dense spherical or elliptoidal aggregates of ER (diameter 2–4 μm) were formed in addition to the randomly distributed ER cisternae characteristic for control cells. The formation of ER aggregates indicates that in spite of an inhibition of the Ca2+ -ATPase in the ER by CPA, membrane synthesis in the ER continued. The ER aggregates are interpreted as a reservoir of ER membrane material newly synthesized during the 2 h CPA-treatment. Hypertrophied Golgi cisternae and secretory vesicles, which are characteristic for secretory cells under control conditions, were completely absent. Additionally the shape of the Golgi stacks was flat and the diameter of the cisternae was shortened by about one third. These phenomena are indicative of an inactive state of the Golgi apparatus. The cellular organization of both other cell types of the root cap, meristematic cells and statocytes, was not visibly affected by CPA, both having a relatively low secretory activity. The formation of ER aggregates as well as the reduction of Golgi compartments are indications for the existence of a unidirectional transport of membrane material from the ER to the Golgi. It is suggested that the membrane traffic from the ER to the Golgi apparatus is regulated by the cytosolic and/or luminal calcium concentration in secretory cells of the root cap.
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    URL: http://dx.doi.org/10.1007/BF01403395
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    Cytological indication of the involvement of calcium and calcium-related proteins in the early responses ofBryonia dioica to mechanical stimulus (1993)
    Springer
    Protoplasma 176 (1993), S. 133-137 
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    ISSN: 1615-6102
    Keywords: Mechanical stimulation ; Bryonia dioica ; Calcium ; Fluorescent probes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The distribution of membrane-bound calium, activated calmodulin, and callose synthesis was visualized inBryonia dioica internodes before and after mechanical stimulus, using fluorescent probes, respectively, chlorotetracycline, fluphenazine, and aniline blue. Bright chlorotetracycline fluorescence remains localized in the plasma membrane of control cells, 30 s after stimulation calcium left the plasmalemma. A delocalization of activated calmodulin was observed after wounding and deposition of callose, which could not be detected before, appeared in the same times in most cells. The callose formation and the decrease in membrane-associated calcium suggest a rapid influx of calcium in the cytosol and an intervention of this ion in the cascade of the early events underlyingBryonia dioica thigmomorphogenesis.
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    URL: http://dx.doi.org/10.1007/BF01378949
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    Effects of changes in environmental calcium on prolactin secretion in Japanese eel, Anguilla japonica (1993)
    Springer
    Journal of comparative physiology 163 (1993), S. 99-106 
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    ISSN: 1432-136X
    Keywords: Prolactin ; Growth hormone ; Calcium ; Pituitary ; Eel, Anguilla japonica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Effects of changes in environmental Ca2+ on the secretion of prolactin, a possible hypercalcemic hormone, were examined both in vivo and in vitro in the Japanese ecl, Anguilla japonica. Transfer of seawater- or freshwater-adapted fish to fresh water, fresh water containing 10 mmol Ca2+ · 1-1 sea water, Ca2+-free sea water, or deionized water was accompanied by significant changes in plasma Ca2+ levels after 7 days, except for the fish transferred from fresh water to fresh water and from sea water to sea water. Changes in external Ca2+ concentrations did not affect plasma prolactin levels, although plasma prolactin levels as well as pituitary prolactin contents were significantly greater in fish in a hypotonic environment than those in a hypertonic environment, regardless of the external Ca2+ concentration. Hypercalcemia, induced by removal of the corpuscles of Stannius, did not alter plasma prolactin levles. Incubation of the pituitary in the medium with different Ca2+ concentrations (up to 2.9 mmol·l-1) did not affect the basal release of prolactin, except at an extremely low Ca2+ concentration (less than 0.1 mmol·l-1) where prolactin release was inhibited. Addition of Ca2+ ionophore (A23187) to the medium led to a marked and significant increase in prolactin release, indicating that an increase in intracellular Ca2+ stimulates prolactin release. However, the effect was not specific to prolactin cells; a similar increase was seen in growth hormone release. These results indicate that changes in environmental Ca2+ concentration may not be the primary factor influencing prolactin secretion in the eel; changes in environmental osmolality or Na+ levels seem to be more critical for the regulation of prolactin secretion.
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    Synergid degeneration in Nicotiana: a quantitative, fluorochromatic and chlorotetracycline study (1992)
    Springer
    Sexual plant reproduction 5 (1992), S. 151-155 
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    ISSN: 1432-2145
    Keywords: Calcium ; Chlorotetracycline ; Fertilization ; Nicotiana ; Synergid degeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Synergid degeneration was examined in the isolated embryo sac and egg apparatus of Nicotiana tabacum using quantitative cytology, fluorochromatic reaction (FCR) and chlorotetracycline (CTC). Most synergid degeneration occurs after pollen tubes (PT) arrive in the ovarian chamber between 42 and 48 h after pollination; synergid degeneration was precluded when PT were prevented from entering the ovary by stylar excision indicating that the signal that triggers synergid degeneration travels only relatively short distances in this plant. There was no evidence for any preferentiality between right or left synergids with regard to cell size or degeneration pattern. FCR staining confirms that synergid degeneration involves the loss of membrane integrity and is a reliable indicator of the onset of degeneration. CTC labeling of the degenerated synergid reveals that a concentrated reserve of membrane-bound calcium is present in the receptive synergid, possibly aiding in the attraction, arrest and discharge of the PT, releasing the sperms into the receptive ES.
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    Regulation of aplanospore germination in Vaucheria (1992)
    Springer
    Planta 188 (1992), S. 279-288 
    Details
    ISSN: 1432-2048
    Keywords: Aplanospore (germination) ; Calcium ; Vaucheria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Germination of aplanospores in Vaucheria longicaulis Hoppaugh var. macounii Blum proceeds through three stages of development. Stage I begins with the initiation of germination and lasts approx. 2 h. During this stage germinating filaments grow at an accelerated rate (266 ± 12 μm · h−1). Stage II is characterized by a sharp decline in the growth rate of germinating filaments (96 ± 4 μm · h−1) and lasts 4 h. This is followed, during the next 4 h, by a recovery in the growth rate (168 ± 8 μm · h−1) of germinating filaments, stage III. Growth rates stabilize and remain unchanged during subsequent development (Oliveira and Fitch, 1988, J. Submicrosc. Cytol. Pathol. 20, 397–406). The Ca2+-influx modulators LaCl3, nifedipine and methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4 (2-trifluoromethylphenyl)-pyridine-5-carboxylate (Bay K-8644), the ionophore calcimycin (A23187), the intracellular Ca2+-release antagonist 8-N-N'-(diethylamino)-octyl-3,4, 5-trimethoxybenzoate (TMB-8), the Ca2+-uptake inhibitor ruthenium red and the phosphoinositide-cycle modulators LiCl and myo-inositol show that the events required for the initiation are distinct from those required for the completion of each stage of germination. These studies in conjunction with microinjection of germinating filaments with inositol 1,4,5-trisphosphate, the natural ligand for Ca2+ release from Ca-storing organelles (endoplasmic reticulum, vacuole), and treatment with chlorotetracycline (CTC), to visualize the distribution of membrane-bound Ca2+ reveal that both the initiation and completion of each stage of germination are controlled by Ca2+ signals which are restricted to well-defined time intervals and are modulated by the origin (source) of Ca2+.
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    Characterization of the epidermis from barley primary leaves (1992)
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    Planta 187 (1992), S. 431-437 
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    ISSN: 1432-2048
    Keywords: Calcium ; Chloride ; Epidermis (leaves) ; Ion compartmentation ; Mesophyll
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The cation and anion distribution between the epidermis and mesophyll of primary leaves of 10-d-old barley (Hordeum vulgare L.) seedlings was studied in relation to growth conditions. A new method was employed to isolate epidermal protoplasts. The following observations were made: (i) Under standard hydroponic growth conditions, K+ was the dominant cation and NO 3 3− the predominant anion, both in epidermal and mesophyll protoplasts. (ii) Levels of Cl− and particularly of Ca2+ were specifically increased in the epidermis when growth conditions stimulated uptake of these ions into the plants. (iii) Epidermal PO 4 3− was maintained at a very low level even in the presence of 50 mM phosphate in the rooting medium, whereas the phosphate concentration in the mesophyll was high, with phosphate being accumulated in the mesophyll vacuoles. (iv) Sulphate and NO 3 − accumulated to a similar degree in the mesophyll and the epidermis when K2SO4 or KNO3 in the rooting medium caused salt stress to the plants. (v) Epidermal protoplasts took up 35SO 4 2− and 36Cl− from the surrounding medium. A comparison of the uptake rates indicates that specific ion deposition into the epidermis may partially be the consequence of differential uptake of ions from the transpiration stream. The results indicate an important function of the epidermis for ion compartmentation in barley leaves.
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    The effect of variation in calcium intake on the growth of wood mice and bank voles (1992)
    Springer
    Oecologia 92 (1992), S. 130-137 
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    ISSN: 1432-1939
    Keywords: Wood mouse ; Bank vole ; Calcium ; Growth ; Body weight
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Calcium intake by wild rodents varies with season and habitat. This may have important ecological consequences; several studies have suggested that calcium availability may limit growth and reproduction. We studied the effect on growth of varying the calcium intake of captive wood mice Apodemus sylvaticus (L.) and bank voles Clethrionomys glareolus (Schreber 1780). To determine whether effects observed in the laboratory could be detected in free-living animals, we also compared the body weights and lengths of free-living animals on calcium-poor gritstone areas with those of rodents on calcium-rich limestone habitats where the dietary calcium concentration was between 2 and 5 times higher. Captive wood mice fed high calcium (0.87%) diet grew at the same rate as mice fed low calcium (0.30%) diet but continued growing for longer, thereby achieving higher asymptotic weights. In contrast, captive bank voles fed the high calcium diet grew more slowly and had lower asymptotic weights than voles fed the low calcium diet. As expected from the laboratory growth study, the higher calcium intake of free-living wood mice on the limestone was associated with greater body size compared with mice on the gritstone. However, bank voles were also larger on the limestone, even though high calcium intake impaired growth in captive animals. The contrast between wood mice and bank voles in the effects of calcium on growth, the reason why impaired growth may not be apparent in bank voles from calcium-rich habitats and the ecological significance of these results are discussed.
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    The latency of the response of Limulus photoreceptors to inositol trisphosphate lacks the calcium-sensitivity of that to light (1992)
    Springer
    Journal of comparative physiology 170 (1992), S. 311-316 
    Details
    ISSN: 1432-1351
    Keywords: Phototransduction ; Limulus polyphemus ; Inositol trisphosphate ; Calcium ; Latency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The latent period before depolarization of Limulus ventral photoreceptors by light flashes was compared with that following brief, intracellular, pressure-injection of d-myo-inositol 1,4,5 trisphosphate. At temperatures between 18 °C and 22 °C and with an extracellular calcium concentration of 10 mM, the responses of 4 cells to light and to injections of 100 μM inositol trisphosphate displayed average latencies of 71 and 56 ms, respectively. The latencies of responses to InsP3 included an estimated 20 ms dead-time inherent in the injection method. Reducing the temperature lengthened the latency of the response to light (Q10 approximately 3.2 between 7 and 22 °C) more than that to inositol trisphosphate (Q10 approximately 2.3). Bathing the photoreceptors in seawater containing no added calcium and 1 mM of the calcium chelator EGTA greatly increased the latency of the light response at all temperatures, but did not increase the latency of the response to inositol trisphosphate. We conclude that the response to inositol trisphosphate lacks the calcium- and temperature-sensitive latent period which characterizes the response to light. If inositol trisphosphate acts, via the release of stored calcium, to stimulate an intermediate in the visual cascade, then that intermediate would appear to be downstream from the latency-generating mechanism.
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    Studies on the effects of Ca2++ and Co++ on the swimming behavior of the blind Mexican cave fish (1992)
    Springer
    Journal of comparative physiology 171 (1992), S. 413-419 
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    ISSN: 1432-1351
    Keywords: Calcium ; Cobalt ; Lateral line ; Behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The hypothesis that the blind cave fish (Astyanax hubbsi) adjusts the level of stimulation to its lateral line system (LLS) by varying its own velocity was examined. When the sensitivity of the LLS sense organs was reduced by lowering the Ca2+ concentration in the water or by adding Co2+ the fish compensated for this by swimming at a higher velocity.
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    Enhancement of sensitivity in photoreceptors of the honey bee drone by light and by Ca2+ (1992)
    Springer
    Journal of comparative physiology 170 (1992), S. 605-613 
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    ISSN: 1432-1351
    Keywords: Phototransduction ; Sensitivity ; Facilitation ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Deeply dark adapted (1 h) photoreceptor cells of the honey bee drone show a light-induced enhancement of sensitivity (facilitation) as an aftereffect of illumination or in the presence of dim backgrounds. The Ca2+-dependency of this effect was studied: Reduction of extracellular Ca2+ to 0.1 mM decreases the sensitivity of a dark adapted cell, and the light-induced increase in sensitivity due to repetitive, dim, 20 ms test flashes is slower than in normal saline. After a sensitizing conditioning light, the sensitivity drops faster in low-calcium saline. The light-induced enhancement of sensitivity is mimicked by pressure injections of low amounts of Ca2+ (Ca2+/EGTA-buffers; 0.15 μM free Ca2+) into a dark adapted cell. Injection of EGTA alone decreases the sensitivity. Injection of a solution containing ca1 mM free Ca2+ sequentially decreases and later increases the sensitivity transiently. These results suggest a model in which a progressive increase in intracellular Ca2+ concentration by light first increases (facilitates), and, at higher concentrations, decreases (light adapts) the sensitivity of the cells. One possible site of action for this positive and negative feedback control of cell sensitivity by Ca2+ is the endoplasmic reticulum.
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    Minimal levels of serum estradiol prevent postmenopausal bone loss (1992)
    Springer
    Calcified tissue international 51 (1992), S. 340-343 
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    ISSN: 1432-0827
    Keywords: Menopause ; Estrogens ; Bone ; Osteoporosis ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Biochemical parameters reflecting bone resorption [urinary calcium/creatinine (Ca/Cr) and hydroxyproline/ creatinine (OH/Cr)] were related to serum estrogens [estrone (E1) and estradiol (E2)] in 262 healthy women including 158 patients receiving estrogen replacement therapy (ERT) for at least 6 months, 49 eugonadal women, and 55 untreated postmenopausal women. A significant (P〈0.001) correlation exists between serum E2 and Ca/Cr: Ca/Cr (mg/dl)=-0.00044 E2 (pg/ml)+0.129 (n=262; r=-0.37), serum E2 and OH/Cr: (OH/Cr (mg/g)=-0.049 E2 (pg/ml)+18.76 (n=262; r=-0.36), serum E1 and Ca/Cr: Ca/Cr (mg/dl)=-0.0003 E1 (pg/ml)+0.127 (n=261; r=-0.28) but not between serum E1 and OH/Cr. Women with circulating levels of E2 between 60 and 90 pg/ml have a significant (P〈 0.01) reduction of Ca/Cr and OH/Cr when compared with those with lower levels of E2. Higher values of E2 do not provide additional benefit. We conclude that in postmenopausal women receiving an estrogen replacement therapy (ERT), a significant reduction of bone resorption is achieved when circulating levels of estradiol reach a value (60 pg/ml) corresponding to the one measured, in eugonadal women, during the last days of the early follicular phase of the menstrual cycle. We suggest that oral or percutaneous ERT should induce a minimal value of 60 pg/ml to prevent postmenopausal bone loss.
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    Changes in the linear attenuation coefficient of canine appendicular bone following intravenous infusion of strontium lactate, measured using gamma-ray computed tomography (1992)
    Springer
    Calcified tissue international 50 (1992), S. 350-356 
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    ISSN: 1432-0827
    Keywords: Computed tomography ; Trabecular bone density ; Strontium ; Calcium ; Atomic absorption spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Changes in the average linear attenuation coefficient (LAC) within a fixed measurement volume in the proximal end of the dog tibia, which contains trabecular bone and associated soft tissues (the trabecular bone “space”), were monitored continuously using gamma-ray computed tomography (γ-CT) prior to, during, and following intravenous infusion of strontium (Sr) lactate. An infusion of 1.3–4.7 g of Sr over a period of 110–160 minutes into 20-kg dogs resulted, within 6–8 hours, in an increase of 0.019–0.045 cm-1 (P〈0.002) in the LAC. Calibration of the γ-CT system showed that 0.44 mg/cm3 of Sr produced a change of 0.01 cm-1 in the LAC. Using this conversion factor, the Sr concentration in the trabecular bone space resulting from infusion, as measured by flame atomic absorption spectroscopy, agreed with that predicted by the change observed in the LAC. Sr present in the serum and urine was consistent with the changes observed in the LAC over the study period. Control dogs infused with mineral-free solutions showed no change in LAC. Calcium equivalents required to give the changes observed in the LAC using Sr indicate that variations in skeletal turnover in man can be monitored in the peripheral skeleton using γ-CT.
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    URL: http://dx.doi.org/10.1007/BF00301633
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    Ca2+ uptake by endoplasmic reticulum of renal cortex. II. Effects of uninephrectomy and parathyroidectomy (1992)
    Springer
    Calcified tissue international 51 (1992), S. 42-47 
    Details
    ISSN: 1432-0827
    Keywords: Kidney ; Endoplasmic reticulum ; Calcium ; In vivo
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Calcium uptake by the endoplasmic reticulum (ER) is important for cellular calcium homeostasis, yet its regulation in nonmuscle cells is poorly understood. We reported that Ca2+ uptake by a light fraction of canine renal cortical ER (LER) is stimulated by protein kinase C in vitro. Here we describe conditions in vivo that stimulated renal cortical LER Ca2+ uptake. Thirty minutes after contralateral nephrectomy in the dog, 45Ca2+ uptake into renal cortical LER was increased 42% above control LER. There was no difference in LER Ca2+ uptake 24 hours after uninephrectomy. Acute denervation did not reproduce the increase in LER 45Ca2+ uptake seen at 30 minutes after uninephrectomy, nor did prior thyroparathyroidectomy abolish it. Forty-eight hours after thyroparathyroidectomy, 45Ca2+ uptake activity into renal cortical LER was decreased ≈sevenfold. In a proximal tubular cell line (LLC-PK1), 30-minute incubation with 12-O-tetradecanoylphorbol-13-acetate doubled 45Ca2+ uptake into a nonmitochondrial pool. Pretreatment with epidermal growth factor halved ER Ca2+ uptake, whereas insulin-like growth factor and growth hormone, alone or in combination, had no effect. Our data suggest that Ca2+ uptake into renal cortical ER is stimulated acutely during compensatory renal growth, perhaps through protein kinase C, and is stimulated chronically by parathyroid hormone.
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    URL: http://dx.doi.org/10.1007/BF00296216
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    Competitive adsorption of magnesium and calcium ions onto synthetic and biological apatites (1992)
    Springer
    Calcified tissue international 51 (1992), S. 143-150 
    Details
    ISSN: 1432-0827
    Keywords: Adsorption ; Magnesium ; Calcium ; Apatite crystals ; Enamel ; Dentin ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Magnesium (Mg) is a conspicuous constituent of hard tissues but its possible role in biomineralization is poorly understood. It is possible that Mg2+ adsorbed onto bioapatites may contribute to the modulation of crystal growth as such inhibitory activity has been reported for synthetic apatites. The present study was undertaken to determine the adsorption isotherms of Mg ions onto synthetic apatites and biominerals in tooth and bone tissues in the presence of other ions of natural occurrence. Synthetic crystals used as adsorbents were hydroxyapatite and, as a better prototype for the biomineral, Mg-containing carbonatoapatite. Human enamel and dentin materials were obtained from extracted, caries-free, permanent teeth. Porcine dentin materials at two developmental stages were obtained from erupted deciduous and unerupted permanent teeth of a 6-month-old slaughtered piglet. Porcine bone was obtained from the cortical portion of the mandible of the same animal. All biomineral samples were pulverized and then treated by plasma ashing (deproteination) at about 60°C. Each of the powdered samples was equilibrated in solutions containing various initial concentrations of Mg2+, Ca2+, and Na+ (or K+) as nitrate salts. Following equilibration, concentrations (and activities) of magnesium and calcium ions in the experimental solution were determined. The pH values of the equilibrium solutions were in the range of 6.2–6.5. Experimental data of the Mg adsorption onto hydroxyapatite were interpreted on the basis of a Langmuir-type model for binary systems assuming competition of Mg2+ and Ca2+ for the same adsorption sites on the crystal surfaces of the apatites. According to this model, the adsorbed Mg is expressed as a function of the ionic activity ratio (Mg2+)/(Ca2+) in the equilibrium solution. The model contains two parameters, the adsorption selectivity constant Ks and the maximum number of adsorption sites N (μmol/g). The numerical values of Ks were similar for all adsorbents used (synthetic and biological) and indicated the preferential adsorption of Ca2+ probably due to spacial restrictions extending to the very surface of the crystals. The initial level of Mg2+ in the surface pool was different in the various biominerals, probably reflecting the composition of fluid in which the biominerals were formed. Whereas the surface pool of Mg of human enamel was marginal, only 5% of the total Mg, significant fractions of the total Mg in human and porcine dentins (about 20–30%), and porcine bone (about 40%) existed on the crystal surfaces. There were significant differences in the total Mg and the value of the parameter N between young (unerupted) and mature (erupted) dentin minerals. It was ascertained that the occupancy of adsorption sites by Mg ions became greater with maturation of the dentin tissues. The overall results suggest that the Mg-mineral interaction in tooth and bone tissues may be a highly tissue-specific process, presumably reflecting differences in fluid composition (particularly Ca and Mg activities) responsible for biomineralization.
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    URL: http://dx.doi.org/10.1007/BF00298503
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    Ca2+ uptake by endoplasmic reticulum of renal cortex. I. Ionic requirements and regulation in vitro (1992)
    Springer
    Calcified tissue international 51 (1992), S. 35-41 
    Details
    ISSN: 1432-0827
    Keywords: Kidney ; Endoplasmic reticulum ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A subcellular fraction enriched in cytochrome c reductase (7.9-fold) and relatively de-enriched (0.64-fold) in Na+/K+-ATPase was prepared from canine kidney cortex by sucrose density gradient ultracentrifugation. It was shown by electron microscopy to consist primarily of a light fraction of endoplasmic reticulum (LER). LER vesicles displayed ATP-dependent 45Ca2+ uptake that was insensitive to 10 mM KCN or NaN3, and was promptly released by 20 μM A23187 or ionomycin. Inositol-1,4,5-trisphosphate (IP3) appeared to produce a time-dependent release of 45Ca2+. Vanadate inhibited 45Ca2+ uptake with a Ki≈0.3 mM, further suggesting that the activity resided in the ER rather than the plasma membrane. 45Ca2+ uptake by LER, at 5 μM total [Ca2+], displayed a strong dependence on divalent cations (Mg2+〉Co2+〉Mn2+≫Ba2+≥Cd2+≥Sr2+, present at 2 mM) as well as on monovalent cations (Na+≥K++Na+ 〉K+〉Li+〉choline+), and anions (Cl-〉acetate-≥NO3 -≥F-〉H2PO4 -≫gluconate-≥oxalate=≫SO4 =). It had a fairly narrow pH optimum (7.25–7.50). Preincubation (10 min) of LER vesicles with 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulated LER Ca2+ uptake; this effect was enhanced in the presence of renal cytosol [5% (vol/vol)]. However, Ca2+ uptake was not affected by preincubation with dibutyryl cyclic AMP, calmodulin, or 1,25-(OH)2-vitamin D3, either in the absence or presence of renal cytosol. Thus, the Mg2+-ATP dependent 45Ca2+ uptake activity of this canine renal cortical LER fraction displays modulation by IP3, TPA, and pH that appears to be physiologically relevant.
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    Acidic phosphoproteins from bone matrix: A structural rationalization of their role in biomineralization (1992)
    Springer
    Calcified tissue international 50 (1992), S. 391-396 
    Details
    ISSN: 1432-0827
    Keywords: Bone ; Matrix ; Phosphoproteins ; Biomineralization ; Calcium ; Nucleation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Osteopontin, bone sialoprotein, and bone acidic glycoprotein-75 are three acidic phosphoproteins that are isolated from the mineralized phase of bone matrix, are synthesized by osteoblastic cells, and are generally restricted in their distribution to calcified tissues. Although each is a distinct gene product, these proteins share aspartic/glutamic acid contents of 30–36% and each contains multiple phosphoryl and sialyl groups. These properties, plus a strict relationship of acidic macromolecules with cell-controlled mineralization throughout nature, suggest functions in calcium binding and nucleation of calcium hydroxyapatite crystal formation. However, direct proof for such roles is still largely indirect in nature. The purpose of this review is to present two speculative hypotheses regarding acidic phosphoprotein function. The goal was to use new sequence information along with database comparisons to develop a structural rationalization of how these proteins may function in calcium handling by bone. For example, our analysis has identified a conserved polyacidic stretch in all three phosphoproteins which we propose mediates metal binding. Also, conserved motifs were identified that are analogous with those for casein kinase II phosphorylation sites and whose number correlates well with that of phosphoryl groups/protein. A two-state conformational model of calcium binding by bone matrix acidic phosphoproteins is described which incorporates these findings.
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    URL: http://dx.doi.org/10.1007/BF00296767
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    Endogenous production of specific antibodies does not decrease hypocalcemic response to calcitonin in young rabbits (1992)
    Springer
    Calcified tissue international 50 (1992), S. 518-520 
    Details
    ISSN: 1432-0827
    Keywords: Calcitonin ; Antibodies ; Calcium ; Osteoporosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary In order to evaluate the potential inhibition of the acute anti-osteoclastic activity of salmon calcitonin (SCT) by specific antibodies (Ab), we compared the SCT-induced hypocalcemic effect in young male rabbits with significant titers of high affinity Ab and in matched animals without Ab. Immunization of rabbits was performed by repetitive s.c. injections of SCT and Freund adjuvant. Ab were present in four-fifths of SCT-treated rabbits (Ab+). Their titer varied from 0.8×10(-9) to 30×10(-9) M/liter and their constant of affinity from 0.97×10(9) to 4.2×10(9) L/M. Intravenous injection of 1 IU/kg SCT to Ab+ rabbits induced a significant decrease (P〈0.01) of ionized serum calcium (Ca2+) after 30 minutes (mean±SD:-9±0.6%) and until the 240th minute of the test (-16.7±4.7%), with a maximum after 120 minutes (-22.6±2%). This was not significantly different from the hypocalcemic effect measured after the same procedure performed in matched animals without Ab (Ab-): significant decrease in Ca2+ (P〈0.01) after 30 minutes (-8.2±2.2%), maximal after 150 minutes (-23.2±4.9%), and lasting until 210 minutes (-14.5±3.7%). We conclude that, in the particular model of the male young rabbit, specific anti-SCT Ab do not block or reduce the acute anti-osteoclastic activity of SCT.
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    URL: http://dx.doi.org/10.1007/BF00582165
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    Regulation of expression by divalent cations of a light-inducible gene in Arthrobacter photogonimos (1992)
    Springer
    Archives of microbiology 158 (1992), S. 85-92 
    Details
    ISSN: 1432-072X
    Keywords: Arthrobacter photogonimos ; lipA Gene ; Photoinduction ; Calcium ; Metals ; Chelation ; Gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Expression of the light-inducible (lipA) gene in Arthrobacter photogonimos is repressed by Ca2+ at a concentration greater than 0.1 μM. Expression of lipA was induced by relatively high concentrations of Zn2+ Ni2+ or Co2+ in cell suspensions, an effect that was blocked by an increase in the concentration of Ca2+ in the medium. Zn2+ and other metals apparently overcame repression by Ca2+ by competing for a cellular binding site. Expression of lipA was also induced when the amount of free Ca2+ was lowered with ethylene-bis (oxyethylenenitrilo)tetraacetic acid (EGTA). Our results show that the lipA gene does not require Zn2+ or other divalent cation for expression and that it is regulated negatively by Ca2+. Accumulation of the mature product of this gene (light-inducible protein, LIP) was minimal in the presence of EGTA. Accumulation increased 10-to 20-fold when divalent cations such as Ca2+, Mn2+, Cu2+ or Zn2+ were added to cell suspensions treated with chelator. These divalent cations, which allowed the protein to achieve a protease-resistant form on the cell surface, could be substituted by protease inhibitors such as antipain, leupeptin or 1,10-phenanthroline. Our data can be explained by a biparous mechanism in which divalent cations regulate both expression of the lipA gene and accumulation of the gene product.
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    A cytochemical study on the role of ATPases during pollen germination in Agapanthus umbelatus L'Her. (1992)
    Springer
    Sexual plant reproduction 5 (1992), S. 138-145 
    Details
    ISSN: 1432-2145
    Keywords: Pollen germination ; ATPases ; Calcium ; Magnesium ; Potassium ; Agapanthus umbelatus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cytochemical detection of ATPase activity in the pollen grain (PG) and pollen tube (PT) of Agapanthus umbelatus showed that the enzymes concerned presented specific patterns of membrane distribution according to their ionic dependencies and to the timecourse of germination and tube growth. In the pollen tubes Ca2+-ATPases were mainly localized in mitochondria and ER membranes, while Mg2+-ATPases were found especially in the tonoplast and in the membrane of the P-particles. K+-ATPases showed a high activity at the plasma membrane. In the pollen grain similar patterns of ATPase activity were observed. The highest activity of all three types was observed at the plasma membrane of the grain and at the intine and inner exine layers of the cell wall. The activity observed in the pollen grain cell wall decreased with germination time. In vivo germination studies in the presence of specific inhibitors of the ATPases showed patterns of inhibition that could be correlated with the corresponding ATPase putative role. The results are discussed in terms of the ultrastructural organization of the PG and PT, especially those correlated with (1) formation and maintenance of ionic gradients throughout the PT, (2) polarized growth and (3) hydrodynamics of PT elongation.
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    URL: http://dx.doi.org/10.1007/BF00194873
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    Changes in calcium and calmodulin levels during microsporogenesis, pollen development and germination in Gasteria verrucosa (Mill.) H. Duval (1992)
    Springer
    Sexual plant reproduction 5 (1992), S. 214-223 
    Details
    ISSN: 1432-2145
    Keywords: Calcium ; Calmodulin ; Microsporogenesis ; Pollen germination ; Gasteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The distribution of membrane calcium and calmodulin (CaM) has been fluorimetrically determined in the anther of Gasteria verrucosa with particular attention to sporogenous cells, meiocytes, microspores, pollen and stages of pollen germination and tube growth using chlortetracycline (CTC) and fluphenazine (FPZ). CTC and FPZ fluorescence in sporogenous cells is relatively higher than in the adjacent tapetal cells, indicating higher membrane calcium and CaM levels in the former cell type. However, during meiosis there is a significant increase in membrane calcium and CaM levels in the meiocytes compared to that found in the young microspores. CTC and FPZ fluorescence in the sporogenous cells, meiocytes and young microspores is punctate and slightly diffused throughout the cytoplasm. In the microspores of the tetrad and the young released microspores CTC fluorescence (CTCf) is polarized and mainly associated with the area opposite the future colporal region. FPZ fluorescence (FPZf) becomes polarized in the young microspore. Subsequently, there is a shift in the polarity, and most of the CTCf and FPZf in the old microspores and pollen is regionalized towards the colporal region, and the fluorescence is more diffused, indicating a change in the organellar-bound calcium and CaM. This final graded distribution of CTCf is maintained during pollen germination in that the growing pollen tubes invariably show a tip to base membrane-calcium gradient. In the tapetal cells a high level of Ca2+ is present during the microspore stage. During the preparation for anthesis the endothecium differentiation is marked by the presence of Ca2+. Post-treatment of labelled cells with a Ca2+ chelator such as EGTA resulted in a substantial decrease in diffuse and punctate CTCf. Alternatively, treatment of cells with non-ionic detergent Nonidet P-40 resulted in the total elimination of CTCf, suggesting that the observed CTC fluorescence was due to membrane-associated calcium. The cytological specification of CTC as a probe for calcium is discussed. From cytofluorometric measurements and atomic absorption, it became clear that the level of Ca2+ in the anther is high during the sporogenous and meiotic phases. An increase in CTCf and FPZf occurred after microspore mitosis. An interaction of Ca2+ transport from tapetum to the young pollen is postulated. These findings suggest that the level of Ca2+ in the anther during meiosis is generally relatively higher than at the sporogenous or young microspore stage. These findings are discussed in the light of available information on the role of Ca2+ and CaM-mediated processes such as cell division, callose synthesis and pollen-tube tip growth.
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    The solubility of CaMoO4(c) and an aqueous thermodynamic model for Ca2+-MoO 4 2 -ion-interactions (1992)
    Springer
    Journal of solution chemistry 21 (1992), S. 525-532 
    Details
    ISSN: 1572-8927
    Keywords: Calcium ; molybdate ; aqueous ; thermodynamic ; complexation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The solubility of powellite [CaMoO4(c)] was studied in aqueous Na2MoO4, CaCl2 and Ca(NO3)2 solutions ranging in concentrations from 1×10−4M to 1.0M and over equilibration times extending to 36 days. Our experimental data were interpreted using the aqueous ion-interaction model of Pitzer and coworkers. The Ca2+−MoO 4 2− ion-interactions were found to be analogous to Ca2+−SO 4 2− . The use of Ca2+−MoO 4 2− ion-interactions parameters (β(0)=0.2, β(1) = 3.1973 and β(2)) and a logK sp of −7.93 gave excellent predictions of all of the experimental data. Commonion ternary interaction parameters such as MoO 4 2− −Cl− or MoO 4 2− −NO 3 − were not required.
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    Effect of cereal-legumechapati diets on absorption and retention of calcium (1992)
    Springer
    Plant foods for human nutrition 42 (1992), S. 165-173 
    Details
    ISSN: 1573-9104
    Keywords: Calcium ; absorption ; wheat ; Bengal gram
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Wheatchapati, wheat+Bengal gram (80∶20 and 70∶30)chapatis and casein diets, at 10 percent protein level, were fed to rats for 12 weeks to study the effect on calcium utilization. The supplementation of Bengal gram to wheat diets significantly improved the calcium absorption. The urinary calcium excretion in wheat+Bengal gramchapati diets was significantly less than that of wheatchapati diet fed group. The in vivo45Ca absorption (CPM/100 μl serum) was also less in wheatchapati group as compared to wheat+Bengal gramchapati diets fed groups. The supplementation of legumes to cereals improved the calcium utilization and it may be concluded that there will be no risk of occurance of protein induced hypercalciuria.
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    Calcium imaging using fluorescence lifetimes and long-wavelength probes (1992)
    Springer
    Journal of fluorescence 2 (1992), S. 47-62 
    Details
    ISSN: 1573-4994
    Keywords: Calcium ; fluorescence lifetime imaging ; calcium imaging ; fluorescence microscopy ; ratiometric imaging ; long-wavelength probes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We describe imaging of calcium concentrations using the long-wavelength Ca2+ indicators, Calcium Green, Orange, and Crimson. The lifetimes of these probes were measured using the frequency-domain method and were found to increase from 50% to severalfold in response to calcium. The two-dimensional images of the calcium concentration were obtained using a new apparatus for fluorescence lifetime imaging (FLIM). We also describe procedures to correct for the position-dependent frequency response of the gain-modulated image intensifier used in the FLIM apparatus. Importantly, the FLIM method does not require the probe to display shifts in the excitation or emission spectra. Using the FLIM method, calcium imaging is possible using probes which display changes in lifetime in response to calcium. Consequently, calcium imaging is possible with excitation wavelengths ranging from 488 to as long as 620 nm, where autofluorescence and/or photochemical damage is minimal. These probes are also suitable for calcium measurements of single cells using lifetime-based flow cytometry.
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    Putative therapeutic applications of calmodulin antagonists (1992)
    Springer
    Pharmacy world & science 14 (1992), S. 161-166 
    Details
    ISSN: 1573-739X
    Keywords: Arrhythmia ; Calcium ; Calmodulin/antagonists & inhibitors ; Cardiomyopathy, congestive ; Drug therapy ; Gastrointestinal diseases ; Hypertension ; Neoplasms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Calmodulin is the most important intracellular receptor protein for the second messenger calcium. The calcium-calmodulin complex regulates a number of physiological processes. An increasing number of pharmaceutical products is reported to interfere with the calcium-calmodulin complex. Despite the fact that the precise mechanisms of action of these so-called calmodulin antagonists await further clarification, reports accumulate in the literature indicating a broadening spectrum of putative therapeutic applications of calmodulin antagonists. Some of these applications, such as in cell proliferation, hypertension, congestive heart failure, arrhythmia and gastro-intestinal disorders, are discussed in the present review.
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    Influence of aluminium and nitrogen on uptake and distribution of minerals in beech roots (Fagus sylvatica) (1992)
    Springer
    Plant ecology 101 (1992), S. 35-41 
    Details
    ISSN: 1573-5052
    Keywords: Acidification ; Calcium ; Localization ; Phosphate ; PIXE ; X-ray-microanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Beech seedlings (Fagus sylvatica L. provenance Västra Torup) were grown in nutrient solution at low pH (4.2) and exposed to AlCl3 and different concentrations of nitrogen. The effects of AlCl3 and nitrogen on uptake of Ca2+ (45Ca) and H2PO4 - (32P) in roots of intact beech were studied. Crossections of roots were analyzed with respect to element concentrations, by use of Mikro-PIXE (particle induced X-ray emission). The distribution of Al, Ca, P, Mg, K, and S was analysed. The experiments were designed to evaluate the effects of aluminium on localization of elements in plant root tissue. Aluminium reduced the concentration of Ca in plants and increased that of K. High nitrogen levels in the solution further decreased the concentration of Ca in the roots. Aluminium (1.0 mM) effectively reduced the Ca2+ (45Ca) uptake in short time experiments. Aluminium accumulated in high concentration (up to 500 μmol/g dry weight in areas of 30×30 μm2) on the root surface, epidermis and outer layers of cortex. Corresponding areas had an extremely low Ca concentration (ca 5 μmol/g dry weight) which could be harmful for regulation of mineral uptake and development of roots. It is concluded that the calcium concentration in roots was reduced by aluminium. The combination with high nitrogen levels further reduced calcium changing the mineral balance which could result in deficiency conditions of calcium in the root.
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    Hydrostatic pressure mimics gravitational pressure in characean cells (1992)
    Springer
    Protoplasma 168 (1992), S. 141-152 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Chara corallina ; Cytoplasmic streaming ; Gravity perception ; Hydrostatic pressure ; Sensory transduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Hydrostatic pressure applied to one end of a horizontalChara cell induces a polarity of cytoplasmic streaming, thus mimicking the effect of gravity. A positive hydrostatic pressure induces a more rapid streaming away from the applied pressure and a slower streaming toward the applied pressure. In contrast, a negative pressure induces a more rapid streaming toward and a slower streaming away from the applied pressure. Both the hydrostatic pressure-induced and gravity-induced polarity of cytoplasmic streaming respond identically to cell ligation, UV microbeam irradiation, external Ca2+ concentrations, osmotic pressure, neutral red, TEA Cl−, and the Ca2+ channel blockers nifedipine and LaCl3. In addition, hydrostatic pressure applied to the bottom of a vertically-oriented cell can abolish and even reverse the gravity-induced polarity of cytoplasmic streaming. These data indicate that both gravity and hydrostatic pressure act at the same point of the signal transduction chain leading to the induction of a polarity of cytoplasmic streaming and support the hypothesis that characean cells respond to gravity by sensing a gravity-induced pressure differential between the cell ends.
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    UV microirradiations elicit Ca2+-dependent apex-directed cytoplasmic contractions in hyphae (1992)
    Springer
    Protoplasma 170 (1992), S. 46-52 
    Details
    ISSN: 1615-6102
    Keywords: Cytoplasmic migration ; Tip growth ; Actin ; Calcium ; UV microirradiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Polarized tip-ward cytoplasmic contractions were induced in hyphae ofSaprolegnia ferax with ultraviolet microirradiations. These unidirectional contractions were similar in appearance and ionic requirements to those previously induced in hyphae ofBasidiobolus magnus, suggesting that the observed inherent cytoplasmic polarity is a general phenomenon. During growth the cytoplasm is continually moving forward with respect to the lateral cell wall and plasma membrane in order to maintain its position in the tip. These contractions may be an exaggerated form of this cytoplasmic migration. F-actin was most concentrated in the contracted cytoplasm, implying that it may be involved in generating the contraction. Contractions were enhanced by external Ca2+ and by irradiating the tip region which is rich in Ca2+ sequestering organelles, suggesting that flooding of the cytoplasm with Ca2+ caused the contractions. H+ did not affect contraction frequency. Neither the change in cytoplasmic consistency that preceded contraction, the contraction itself, nor the F-actin damage induced were confined to the microirradiated zone. This is in keeping with irradiation-induced damage to a network under tension or a flux of diffusible ions causing the response. Thus Ca2+ may regulate actin-myosin interactions that generate cytoplasmic migration.
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    Scale biogenesis in the green alga,Mesostigma viride (1992)
    Springer
    Protoplasma 167 (1992), S. 19-32 
    Details
    ISSN: 1615-6102
    Keywords: Scales ; Golgi apparatus ; Vacuole ; Calcium ; Vesicle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The unicellular green algal flagellate,Mesostigma viride, is characterized by an extracellular matrix of multiple layers of scales. These scales are processed within the Golgi apparatus (GA). The GA consists of 11–13 closely stacked cisternae. The cis cisternae are highly fenestrated and grow via vesicles from adjacent transition ER. Medial-trans cisternae are plate-like with swollen peripheries. The calcified basket scales are produced in the peripheries of GA cisternae, usually first observable in the medial zone of the cisternal stack. Cisternal membrane closely conforms to the precise architecture of the developing scale. Antimonate labeling reveals that a population of smooth cytoplasmic vacuoles situated near the GA contains a store of calcium, perhaps used for scale processing. Vesicles carry calcium from these vacuoles to the cisternal loci where basket scale ontogenesis is occurring. The smaller scale types are produced within the central areas of the GA. A discussion concerning membrane flow through the GA is provided.
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    Activation of two types of fibres in ferret, Mustela putorius furo, cremaster muscle (1992)
    Springer
    Journal of comparative physiology 162 (1992), S. 111-118 
    Details
    ISSN: 1432-136X
    Keywords: Cremaster ; Ferret ; Skeletal muscle ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Some contractile, histochemical, morphological and electrophysiological properties of ferret, Mustela putorius furo, cremaster muscle have been estimated. Histochemical fibre typing revealed the presence of two types of fibres (type I 66.2%, type II 33.8%). Morphometry performed on ATPase-stained transverse sections showed that type I was composed of a large amount (40%) of small(〈400 μm2) cells. In mammalian Ringer two groups of fibres could be recognized on the basis of the values of resting potential (-69.7 mV and-59.1 mV) and intracellular sodium activity (8.3 mmol·l-1 and 14.1 mmol·l-1, respectively). In experiments on fibre bundles, the elevation of extracellular potassium concentration to 15–200 mmol·l-1 produced contractures that consisted of a well-defined transient or phasic tension followed by a sustained or tonic tension. Properties of activation and inactivation of the tension analysed in small bundles of cut fibres (lengths 0.5–1.0 cm) were of fast- and slow-twitch type for phasic and tonic phase, respectively. In contrast to the phasic component of K contractures, the tonic phase was abolished by Ca2+ withdrawal and inhibited by Ni2+, Cd2+, Co2+, Gd3+ and gallopamil (D600). In Ca2+-free medium the sustained tension was restored by adding Sr2+. It is concluded that in ferret cremaster muscle the presence of slow-twitch fibres would give rise to the tonic component of the K contracture in which an extracellular source of activator Ca2+ is involved. The ability of these fibres to contract with a maintained tension for prolonged periods of time might participate in the temperature regulation of the testes.
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    URL: http://dx.doi.org/10.1007/BF00398336
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    Cellular mechanisms of paired electrical stimulation in ferret ventricular myocardium: relationship between myocardial force and stimulus interval change (1992)
    Springer
    Journal of comparative physiology 162 (1992), S. 401-407 
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    ISSN: 1432-136X
    Keywords: Aequorin ; Calcium ; Sarcoplasmic reticulum ; Paired stimulation ; Ferret, Mustela putorius furo
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The subcellular mechanisms of twitch-force potentiation with paired electrical stimulation was studied in ferret ventricular myocardium using the bioluminescent calcium indicator aequorin. It is demonstrated for the first time that interpolation of an extrasystole in a train of conditioned twitches results in a beat-to-beat change in [Ca2+]i and force. Steady-state twitch force and Ca i 2+ were increased with paired stimulation. Increased [Ca2+]0 in the setting of paired stimulation resulted in an increase in the amplitude of the postextrasystole and associated Ca2+ transient. Verapamil, a Ca2+ channel antagonist, had the opposite effect of increased [Ca2+]0. Postextrasystole potentiation was still present, but diminished in amplitude. These results indicate that postextrasystole potentiation is in part due to a verapamil-depletable store (Ca2+). Postextrasystole potentiation is therefore predominantly dependent on sarcoplasmic reticulum (SR) Ca2+ loading. Ryanodine, an alkaloid which induces Ca2+ leakage from the SR, abolished postextrasystole potentiation; however, in the presence of ryanodine the extrasystole was potentiated. Caffeine, a phosphodiesterase inhibitor which induces SR Ca2+ release and impairs uptake, also abolished postextrasystole potentiation. As with ryanodine there was resultant potentiation of the extrasystole. In the case of caffeine the calcium transient consisted of a second slow component associated with extrasystole twitch potentiation. The results are consistent with sarcolemmal Ca2+ influx playing a role in potentiation of the extrasystole in the presence of an impaired SR. These data indicate that transsarcolemmal Ca2+ influx in the presence of impaired intracellular Ca2+ buffering can directly activate the myofilaments in agreement with reports on human myocardium.
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    URL: http://dx.doi.org/10.1007/BF00258961
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    Accumulation of calcium and phosphorus in pigeon (Columba livia) embryos (1992)
    Springer
    Journal of comparative physiology 162 (1992), S. 535-538 
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    ISSN: 1432-136X
    Keywords: Embryo ; Calcium ; Phosphorus ; Altricial ; Pigeon, Columba livia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Calcium and phosphorus were measured in the yolk and albumen of fertile pigeon (Columba livia) eggs incubated for 0–17 days, and in embryos and hatchlings. Shell provided most of the calcium for skeletal mineralization of the embryos, whereas phosphorus was derived from the yolk and albumen. Mobilization of calcium from the shell to the embryo commenced at approximately day 11 of incubation, accumulating both in the embryo and the yolk sac. There was 1.4 times more calcium in squab yolk sacs than that contained in newly laid egg yolks. The results suggest that whereas general patterns of calcium and phosphorus accumulation during embryogenesis in altricial birds closely resemble those of precocial birds, calcium mobilization from the shell begins later, proceeds at a slower rate and results in a less mineralized hatchling.
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    URL: http://dx.doi.org/10.1007/BF00264814
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    Ammonium and nitrate uptake rates and rhizosphere pH in non-mycorrhizal roots of Norway spruce [Picea abies (L.) Karst.] (1991)
    Springer
    Trees 5 (1991), S. 14-21 
    Details
    ISSN: 1432-2285
    Keywords: Ammonium ; Calcium ; Nitrate ; Picea abies ; Rhizosphere pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Relationships between root zone temperature, concentrations and uptake rates of NH 4 + and NO 3 − were studied in non-mycorrhizal roots of 4-year-old Norway spruce under controlled environmental conditions. Additionally, in a forest stand NH 4 + and NO 3 − uptake rates along the root axis and changes in the rhizosphere pH were measured. In the concentration (Cmin) range of 100–150 μM uptake rates of NH 4 + were 3–4 times higher than those of NO 3 − The preference for NH 4 + uptake was also reflected in the minimum concentration (Cmin) values. Supplying NH4NO3, the rate of NO 3 − uptake was very low until the NH 4 + concentrations had fallen below about 100 μM. The shift from NH 4 + to NO 3 − uptake was correlated with a corresponding shift from net H+ production to net H+ consumption in the external solution. The uptake rates of NH 4 + were correlated with equimolar net production of H+. With NO 3 − nutrition net consumption of H+ was approximately twice as high as uptake rates of NO 3 − In the forest stand the NO 3 − concentration in the soil solution was more than 10 times higher than the NH 4 + concentration (〈100 μM), and the rhizosphere pH of non-mycorrhizal roots considerably higher than the bulk soil pH. The rhizosphere pH increase was particularly evident in apical root zones where the rates of water and NO 3 − uptake and nitrate reductase activity were also higher. The results are summarized in a model of water and nutrient transport to, and uptake by, non-mycorrhizal roots of Norway spruce in a forest stand. Model calculations indicate that delivery to the roots by mass flow may meet most of the plant demand of nitrogen and calcium, and that non-mycorrhizal root tips have the potential to take up most of the delivered nitrate and calcium.
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    Receptor potential and light-induced mitochondrial activation in blowfly photoreceptor mutants (1991)
    Springer
    Journal of comparative physiology 168 (1991), S. 305-312 
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    ISSN: 1432-1351
    Keywords: Blowfly ; Photoreceptor ; Receptor potential ; Mitochondrial activation ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Simultaneous measurements of the receptor potential and the light-induced mitochondrial activation were performed in white-eyed blowflies Calliphora vicina, mutant chalky, and Lucilia cuprina, mutants w F and w'nss. The intensity dependence and the temporal dynamics were investigated. 2. The characteristic curve of the light-induced mitochondrial activation vs. log intensity has an S-like shape, which is much steeper than the characteristic curve of the receptor potential (the V/log I curve). The threshold intensity of mitochondrial activation elicits about a half-maximal receptor potential, while mitochondrial activation and photoreceptor potential saturate at about the same intensity. 3. The time course of the mitochondrial activation induced by a light flash, i.e. the pulse-response curve, is biphasic in both mutants with normal phototransduction properties, Calliphora chalky and Lucilia w F ; the shape is slightly species dependent. 4. In the phototransduction mutant Lucilia w'nss the step-responses of both the (bright) light-induced mitochondrial activation and receptor potential are quite different from the corresponding signals in Lucilia w F . The striking resemblance of the step-response of the mitochondrial activation to its pulse-response indicates that mitochondrial activation and receptor potential are intimately linked.
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    Light-induced extracellular calcium and sodium concentration changes in the retina of Calliphora: involvement in the mechanism of light adaptation (1991)
    Springer
    Journal of comparative physiology 169 (1991), S. 299-311 
    Details
    ISSN: 1432-1351
    Keywords: Fly photoreceptor ; Light adaptation ; Calcium ; Sodium ; Pigment granule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Ion-selective microelectrodes inserted into the compound eyes of Calliphora were used to monitor the changes in extracellular concentration of Ca2+ and Na+ (Cao, Nao) brought about by a 1-min exposure to white light (maximal luminous intensity ≈0.1 cd/cm2). Using Ringer solution as the reference (Ca2+ = 1 mM), the dark concentration of the calcium in the retina was found to be (1.4 ± 0.4) mM (n=12). Stimulation with light reduces Cao. At intensities near maximal the Cao signal is phasic, reaching a transient minimum about 6 s after light onset $$(\Delta {\text{Ca}}_{\text{o}} {\text{ = }} - 6.28\% \pm 1.6\% ,{\text{ }}n = 20)$$ and then rising to a nearly stable plateau below the dark level (-3.3% ± 2.6%). Cao signals measured in the white-eyed mutant (chalky), which lacks pigment granules, are comparable to those in the wild type. Conclusions: (a) There are no extracellular Ca2+ binding sites that regulate light adaptation, such as were postulated by Hochstrate and Hamdorf (1985). (b) Ca2+ influx into the photoreceptors seems to be necessary for light adaptation, (c) The pigment granules have no major function in intracellular calcium regulation. The time course of the Nao signals resembles that of the Cao signals. Because the percentage concentration change is small, light-induced extracellular Na+-depletion cannot contribute to a reduced response amplitude at light adaptation.
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    Photophysiology of turion germination in Spirodela polyrhiza (L.) Schleiden VIII. Calcium dependence and β-amylase activity (1991)
    Springer
    Planta 186 (1991), S. 81-87 
    Details
    ISSN: 1432-2048
    Keywords: β-Amylase ; Calcium ; Germination (turions) ; Phytochrome ; Signal transduction ; Turion ; Spirodela
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Red-light-induced germination (via phytochrome) of turions of Spirodela polyrhiza (L.) Schleiden, strain SJ, showed an absolute requirement for exogenously applied calcium (Appenroth et al. 1990b, Biochem. Physiol. Pflanzen 186, 209–219). With calcium step-up experiments (from 0.9 μM to 1 mM Ca2+) the influence of Ca2+ on the escape from far-red-light reversibility was investigated. Delaying the time of Ca2+ application after the red light pulse resulted in an increased reversibility. This confirmed that the calcium-requiring phase is within the phytochrome-dependent period. Ten days after a red light pulse was applied the activity of β-amylase (EC 3.2.1.2) was increased about tenfold. The starting point was similar in the germination and enzymatic responses, but half-maximal response times according to the Mitscherlich function (2.5 d and 6.9 d, respectively) and times of saturation (about 6 d and 9 d, respectively) were different. Increase of β-amylase activity was completely inhibited by irradiation with far-red light (demonstrating phytochrome as the photoreceptor), as well as by inhibitors of translation (cycloheximide, puromycin) and transcription (cordycepin). Once formed, the active enzyme protein was stable for at least 4 d after cycloheximide application. After application of cordycepin a small amount of translation activity was detected until complete inhibition was reached after 2 d. This phytochrome-modulated, de-novo synthesis of β-amylase was only slightly dependent on exogenous Ca2+. Therefore, it can be concluded that the phytochrome-mediated signal-transduction chain branches either in its reversible part or as a consequence of diversity of the primary phytochrome reaction.
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    Calcium-dependent phospholipid-binding proteins in plants (1991)
    Springer
    Planta 184 (1991), S. 67-73 
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    ISSN: 1432-2048
    Keywords: Annexin ; Calcium ; Exocytosis ; Phospholipid-binding proteins ; Zea (annexins)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract There is evidence that Ca2+ can regulate vesicle-mediated secretion in plant cells, but the mechanism for this is not known. One possibility is that Ca2+ -dependent phospholipid-binding proteins (annexins) couple the Ca2+ stimulus to the exocytotic response. Using a protocol developed for the isolation of animal annexins we have identified proteins in maize (Zea mays L.) coleoptiles that have similar characteristics to annexins. The predominant polypeptide species run as a doublet of relative molecular mass (Mr) 33000–35000 on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE); another less-abundant protein of Mr 23000 is also present. In the presence of Ca2+ these proteins bind to liposomes composed of acidic phospholipids. Calcium-sensitivity of binding differs for each protein and is also influenced by the pH of the buffer used for the liposome-binding assay. Antiserum raised to the 33 to 35-kDa doublet purified on SDS-PAGE recognises the doublet in crude extracts from maize and proteins of similar Mr in Tradescantia virginiana and tobacco Nicotiana tabacum L. The antiserum also recognises p68 (Annexin VI) from chicken gizzard extracts, indicating homology between animal annexins and the maize proteins. For the maize proteins to be involved in the regulation of exocytosis, binding to phospholipids would be expected to occur at physiological levels of Ca2+. The characteristics of the maize annexin-like proteins are described and attention drawn to the marked effect of pH in lowering the requirement for Ca2+ for phospholipid binding.
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    Complementary analysis of freeze-dried and frozen-hydrated plant tissue by electron-probe X-ray microanalysis: Spectral resolution and analysis of calcium (1991)
    Springer
    Planta 184 (1991), S. 327-333 
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    ISSN: 1432-2048
    Keywords: Calcium ; Electron-probe ; Lactuca ; Mineral elements (microanalysis) ; X-ray microanalysis for mineral elements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Automated methods of peak determination including peak location, background determination and peak deconvolution are presented. Special attention is given to the problem of severely overlapped peaks, such as the primary calcium peak (Caka) and the secondary potassium peak (Kkβ). A method, based on the principle of electronic transitional probabilities, is presented for estimating Ca in the presence of a high background of K, and limitations of resolution are discussed. Minimally detectable concentrations of elements in prepared frozen-hydrated standards are estimated empirically by analysis of the relative variance. Minimally detectable Ca is estimated in both frozen-hydrated and freeze-dried tissue standards. Using our instrumentation and procedures P, S, Cl and K are detectable down to 24 mM, while Na and Mg are only detectable down to 38 mM in frozen-hydrated tissue. In the presence of 100 mM K, detection of calcium is possible down to 22 and 2 mM in frozen-hydrated and freeze-dried tissue, respectively. As an example, total Ca is shown not to conform to the radial gradient of K across the lettuce (Lactuca sativa L.) taproot.
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    The effect of habitat geology on calcium intake and calcium status of wild rodents (1991)
    Springer
    Oecologia 88 (1991), S. 539-546 
    Details
    ISSN: 1432-1939
    Keywords: Wood mouse ; Bank vole ; Calcium ; Femur ; Ash
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Calcium is essential for normal physiological function, reproduction and growth in mammals but its distribution in the natural environment is heterogeneous. Spatial variation in calcium soil content is especially marked in the Peak District, United Kingdom, where both calcium-rich limestone and calcium-poor gritstone rock types occur. Wood mice Apodemus sylvaticus (L) and bank voles Clethrionomys glareolus (Schreber 1780) from limestone areas had significantly higher calcium concentrations in stomach contents and in faeces compared with their counterparts from gritstone areas. Calcium status was assessed from serum calcium concentration, femur weight, ash content of the body, calcium concentration in the femur and body ash. There was no significant difference in serum calcium concentration, femur calcium concentration and body ash calcium concentration between animals from the limestone and the gritstone. However, on the limestone, bank voles, but not wood mice, had significantly heavier femora and a greater proportion of ash in the body compared with their gritstone counterparts.
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    Cell cycle-related fluctuations in transcellular ionic currents and plasma membrane Ca2+/Mg2+ ATPase activity during early cleavages of Lymnaea stagnalis embryos (1991)
    Springer
    Development genes and evolution 200 (1991), S. 120-131 
    Details
    ISSN: 1432-041X
    Keywords: Ionic currents ; Ca2+/Mg2+ ATPase ; Molluscan eggs ; Cell cycle ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary During the first four mitotic division cycles of Lymnaea stagnalis embryos, we have detected cell cycle-dependent changes in the pattern of transcellular ionic currents and membrane-bound Ca2+-stimulated ATPase activity. Ionic currents ranging from 0.05 to 2.50 μA/cm2 have been measured using the vibrating probe technique. Enzyme activity was detected using Ando's cytochemical method (Ando et al. 1981) which reveals Ca2+/Mg2+ ATPase localization at the ultrastructural level, and under high-stringency conditions with respect to calcium availability, it reveals Ca2+-stimulated ATPase. The ionic currents and Ca2+-stimulated ATPase localization have in common that important changes occur during the M-phase of the cell cycles. Minimal outward current at the vegetal pole coincides with metaphase/anaphase. Maximal inward current at the animal pole coincides with the onset of cytokinesis at that pole. Ca2+-stimulated ATPase is absent from one half of the embryo at metaphase/anaphase of the two- and four-cell stage, whereas it is present in all cells during the remaining part of the cell cycle. Since fluctuations of cytosolic free calcium concentrations appear to correlate with both karyokinesis and cytokinesis, we speculate that part of the cyclic pattern of Ca2+-stimulated ATPase localization and of the transcellular ionic currents reflects the elevation of cytosolic free calcium concentration during the M-phase.
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    Localized activity of Ca2+-stimulated ATPase and transcellular ionic currents during mesoderm induction in embryos ofLymnaea stagnalis (Mollusca) (1991)
    Springer
    Development genes and evolution 200 (1991), S. 320-329 
    Details
    ISSN: 1432-041X
    Keywords: Ionic currents ; Ca2−/Mg+ ATPase ; Molluscan embryo ; Mesoderm induction ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary InLymnaea stagnalis, mesoderm induction occurs at the 24-cell stage, when the apical tip of the macromere 3D establishes a close contact with a number of micromeres. Via its tip, the macromere 3D is supposed to receive an inductive signal from the micromeres, resulting in the determination of the mesodermal stem cell 4d at the next division. In view of the possibility that transcellular ionic currents might somehow be involved, either in the processes that bring about this particular configuration of blastomeres or in the induction process itself, we mapped the electric field around the embryo during the 24-cell stage, using a vibrating probe. We detected a reversal of the current direction as compared to the uncleaved egg, whilst the polarity of the field along the animal-vegetal axis was maintained. We also mapped the localization of Ca2+-stimulated AT-Pase, an enzyme that drives the Ca2+-efflux from the cell. We found that this enzyme is localized exclusively along the cytoplasmic face of the apical plasma membrane of macromere 3D, and that its presence is restricted to the period from 110 to 135 min after the fifth cleavage, when there is close contact between macormere 3D and the micromeres. Since the localization of the Ca2+-stimulated ATPase coincides both in time and space with the induction of the mesoderm-mother cell, we suggest that localized calcium fluxes may play a role in this induction process.
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    Electrotropism of pollen tubes of camellia and other plants (1991)
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    Sexual plant reproduction 4 (1991), S. 138-143 
    Details
    ISSN: 1432-2145
    Keywords: Calcium ; Camellia japonica ; Electrotropism ; Pollen tube
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Pollen tubes of Camellia japonica grew toward the cathode upon exposure to an electric field. Reversal of the field direction during the course of tube growth also reversed the direction of tube growth. These observations demonstrate the existence of the electrotropism of pollen tubes. This electro tropic response was confirmed in several kinds of pollen. The direction that the growing tube turned was found to differ with different pollen species, but it did not vary in those of the genus Camellia. The curvature in response to the electrotropic stimulus was influenced by calcium ion concentration as well as by the strength of the applied fields. The optimum condition for each was studied. The degree of tube extension decreased generally in inverse proportion to current density.
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    Calcium inhibition of efrotomycin production byNocardia lactamdurans (1991)
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    Journal of industrial microbiology and biotechnology 7 (1991), S. 41-44 
    Details
    ISSN: 1476-5535
    Keywords: Efrotomycin ; Calcium ; Nocardia lactamdurans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Efrotomycin is a modified polyketide antibiotic of the elfamycin family that has use in the area of pig husbandry. Optimization of the fermentation medium for production of efrotomycin byNocardia lactamdurans revealed that the fermentation is sensitive to hard water and certain lots of cottonseed flour used to prepare a complex fermentation medium. A limited metal ion analysis of the hard water indicated that calcium ions are present at concentrations found to be inhibitory by the addition of calcium chloride to medium prepared with distilled water. Similarly, a correlation between lots of cottonseed flour that poorly supported the fermentation and high calcium levels is presented. Further experimentation revealed that by altering the sterilization conditions of the cottonseed flour, the inhibitory effect of poor lots could be prevented.
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    Calcium-regulated appressorium formation of the entomopathogenic fungusZoophthora radicans (1991)
    Springer
    Protoplasma 160 (1991), S. 77-88 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Calmodulin ; Appressorium formation ; Zoophthora radicans ; Entomopathogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The fungusZoophthora radicans (Zygomycetes: Entomophthorales) requires external Ca2+ for appressorium formation but not for conidial germination. The number of appressoria formed depends on the Ca2+ concentration of the medium. At low [Ca2+] (100 pM) nuclear division and germ tube growth are significantly reduced compared to higher Ca2+ concentrations (10 and 1,000 μM). By contrast, neither external K+ nor external Cl− is needed for germination or appressorium formation. Treatment of conidia with a Ca2+-antagonist, Nd3+, and a Ca2+-channel blocker, nifedipine, inhibits appressorium formation, showing that a Ca2+ influx is required for appressorium formation. Furthermore, the partial yet saturating inhibition by nifedipine and complete inhibition by Nd3+ indicates that at least two kinds of Ca2+ channels are involved in appressorium formation. A contribution of intracellular Ca2+ to the signal transduction chain for the formation of appressoria is demonstrated by the inhibitory effect of the intracellular Ca2+ antagonist TMB-8. The calmodulin antagonists R24571, TFP, W-7, and W-5 inhibit appressorium formation at concentrations which have no effect on germination. The data presented in this paper are consistent with the hypothesis that a Ca2+/calmodulin system is involved in regulating appressorium formation. However, since the direct effects of the drugs were not specifically tested on their proposed binding sites, we leave room for alternative hypotheses that have yet to be formulated.
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    Alkaline earth metal content of human bones at the site of «S'Illot des Porros» (Iron age, Mallorca, Spain) (1991)
    Springer
    International journal of anthropology 6 (1991), S. 225-231 
    Details
    ISSN: 1824-3096
    Keywords: Strontium ; Barium ; Calcium ; Human Diet ; bone ; Mollusc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The aim of this study is to establish the basic diet of the people inhumed at the site of Porros by analysing some of the alkaline earth metals present in human and animal bones. The site is a Talayotic necropolis established in the small island of «S'Illot des Porros» (Mallorca, Spain) during the 6th to 2nd century B.C. In this island the only evidence of human activity to be found is the necropolis; the corresponding settlement site is unknown. The results show that the diet of these people was based on a fundamentally marine economy perhaps mollusc collecting. This outcome agrees with a coastal location for the settlement site.
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    Calcium handling in myocardium from amphibian, avian, and mammalian species: the search for two components (1991)
    Springer
    Journal of comparative physiology 161 (1991), S. 19-25 
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    ISSN: 1432-136X
    Keywords: Aequorin ; Calcium ; Sarcoplasmic reticulum ; Contraction ; Excitation-contraction coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Steps involved in excitation-contraction coupling in mammalian myocardium have been derived using a relatively limited number of animal species. However, the use of animal models for investigations into excitation-contraction coupling in normal and disease states has encompassed a wide range of animal species. We addressed the question as to whether excitation-contraction coupling as currently understood applies to intracellular calcium handling in myocardium from multiple mammalian species, amphibian, and avian myocardium. The bioluminescent calcium indicator aequorin was used to record intracellular calcium transients in both ventricular and atrial tissue. We report that in all mammalian and avian species studied the calcium transient recorded in both ventricular and atrial myocardium is monophasic and reflects calcium release and re-uptake by the sarcoplasmic reticulum. In contrast, the Ca2+ transient recorded from salamander myocardium is prolonged relative to mammalian and avian myocardium, and appears to reflect in part trans-sarcolemmal calcium entry. Only in diseased myocardium derived from human and swine myocardium was a second component detected in the calcium transient. These data indicate that sarcoplasmic reticulum calcium handling is pivotal in excitation-contraction coupling for multiple species with differing physiologies. Also, in disease states, intracellular calcium handling is often affected with resultant alterations in the time-course and/or configuration of the calcium transient.
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    URL: http://dx.doi.org/10.1007/BF00258742
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    Patterns of mobilization of calcium, magnesium, and phosphorus by embryonic yellow-headed blackbirds(Xanthocephalus xanthocephalus) (1991)
    Springer
    Journal of comparative physiology 160 (1991), S. 649-654 
    Details
    ISSN: 1432-136X
    Keywords: Aves ; Calcium ; Embryo ; Growth ; Magnesium ; Phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Embryonic blackbirds(Xanthocephalus xanthocephalus) obtain most of their calcium from the eggshell (85 90%), but all of their phosphorus comes from reserves in the yolk (80–85%) and albumen (15–20%). Approximately equal amounts of magnesium are supplied by the eggshell, the yolk, and the albumen. Yolk is depleted of magnesium and phosphorus during embryogenesis, but excess calcium absorbed from the eggeshell is stored in the yolk. Consequently reserves of calcium in the yolk actually increase 8-fold during embryonic development. Our results reveal that altricial birds manifest patterns of mobilization and deposition of calcium and other elements similar to those described for precocial species. Evolution of altriciality from precocity evidently did not entail major changes in how embryonic birds meet the challenge of obtaining the calcium, magnesium, and phosphorus required for development.
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    URL: http://dx.doi.org/10.1007/BF00571263
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  • 87
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    Calcium content and concretions of pineal glands of young and old rats (1991)
    Springer
    Cell & tissue research 263 (1991), S. 593-596 
    Details
    ISSN: 1432-0878
    Keywords: Pineal gland ; Concretions ; Calcium ; X-ray microanalysis ; Rat (Wistar)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Calcium content and pineal concretions were studied in young (2–3 months) and old (28 months) Wistar rats. Samples, deep-frozen by liquid propane/isopentane and freeze-dried were analysed by means of X-ray microanalysis in a scanning electron microscope. Total semi-quantitative measurements revealed that pineals of old rats showed a marked increase of calcium compared with the pineals of young rats. It is thus suggested that a calcium-rich environment is responsible for the growth of pineal concretions, which only appear in old rats. Pineal calcifications in rats could thus be an indicator of aging and/or of a degenerating state.
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    URL: http://dx.doi.org/10.1007/BF00327294
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  • 88
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    Seasonal variation of calcium, magnesium, potassium, and manganese contents in xylem sap of beech(Fagus sylvatica L.) in a 35-year-old limestone beech forest stand (1990)
    Springer
    Trees 4 (1990), S. 75-80 
    Details
    ISSN: 1432-2285
    Keywords: Calcium ; Fagus sylvatica ; Magnesium ; Manganese ; Mineral content ; Potassium ; Seasonalvariation ; Xylem sap
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary In a 35-year-old calcareous beech forest stand five beech trees (Fagus sylvatica L.) were felled every 2 weeks, and xylem sap was obtained by means of water displacement from the lowest trunk sections, each 100 cm in length. From mid-October 1988 to mid-October 1989 a total of 130 trees were investigated. The seasonal variations of the Ca, Mg, K and Mn contents, as well as those of pH, show four characteristic phases. Additionally, distribution of the mineral contents along the trunk was studied in four trees. The seasonal increase and decrease of xylem sap mineral contents along the trunk is shown for the characteristic phenophases. The Ca, Mg, K, and Mn contents of xylem saps were determined by means of atomicabsorptionspectrophotometry.
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    URL: http://dx.doi.org/10.1007/BF00226069
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  • 89
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    Relatively high calcium is localized in synergid cells of wheat ovaries (1990)
    Springer
    Sexual plant reproduction 3 (1990), S. 98-102 
    Details
    ISSN: 1432-2145
    Keywords: Synergids ; Calcium ; Chemotropism ; Fertilization ; Energy-dispersive X-ray microanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Using energy-dispersive X-ray microanalysis of mature, unpollinated wheat ovaries fixed by freeze-substitution, we show here that the synergid cells store a relatively high concentration of calcium. Based on our results and other indirect evidence, we suggest that supraoptimal levels of calcium in synergids may regulate: (1) correct orientation of the pollen tube, by forming a calcium gradient in the vicinity of the synergids, and (2) arrest and rupture of the pollen tube to release the sperm near the egg.
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    URL: http://dx.doi.org/10.1007/BF00198852
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  • 90
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    Effects of calcium input/output on the stability of a system for calcium-regulated viscoelastic strain fields (1990)
    Springer
    Journal of mathematical biology 28 (1990), S. 585-593 
    Details
    ISSN: 1432-1416
    Keywords: Calcium ; Viscoelasticity ; Stability ; Pattern generation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The Goodwin and Trainor model of pattern generation in calcium-regulated strain fields is studied in the case where calcium input and calcium output processes are involved. It is shown that the properties of the original model may still remain provided that the input-output processes are not unstable. In this last case, despite the eventual stabilizing effect of the calcium exchange term, perturbations of the generalized system can grow and lead to inhomogeneous solutions. Applications to cell differentiation and cell growth are discussed.
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    URL: http://dx.doi.org/10.1007/BF00164164
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  • 91
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    Calcium increases the yield of somatic embryos in carrot embryogenic suspension cultures (1990)
    Springer
    Plant cell reports 9 (1990), S. 221-223 
    Details
    ISSN: 1432-203X
    Keywords: Calcium ; Daucus carota ; Somatic embryogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An upward shift in the concentration of calcium present in the medium during somatic embryogenesis increased the number of embryos produced approximately two-fold. This was observed when embryogenic suspension cells grown in 2,4-D medium with the normal calcium concentration of 10−3 M were transferred to hormone-free medium containing 10−2 M calcium and when embryogenic suspension cells grown in 2,4-D medium containing 10−4 M calcium were transferred to hormone-free medium with 10−3 M calcium. At calcium concentrations between 6·10−3 and 10−2 M globular stage somatic embryos were found in cultures supplemented with 2·10−6 M of 2,4-D indicating that elevated calcium counteracts the inhibitory effect of 2,4-D on somatic embryogenesis. No qualitative changes were found in the pattern of extracellular polypeptides as a result of growth and embryogenesis in media with different calcium concentrations.
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    URL: http://dx.doi.org/10.1007/BF00232184
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  • 92
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    Polar localization of plasma membrane Ca2+/Mg2+ ATPase correlates with the pattern of steady ionic currents in eggs ofLymnaea stagnalis andBithynia tentaculata (Mollusca) (1990)
    Springer
    Development genes and evolution 199 (1990), S. 134-145 
    Details
    ISSN: 1432-041X
    Keywords: Ca2+/Mg2+ ATPase ; Molluscan eggs ; Ionic currents ; Polarity ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary During extrusion of the first polar body in eggs ofLymnaea stagnalis andBithynia tentaculata a localized Ca2+ /Mg2+ ATPase activity was detected, using Ando's enzyme-cytochemical method for electron microscopy [Ando et al. (1981) Acta Histochem Cytochem 14:705–726]. The enzyme activity was distributed in a polar fashion, along the cytoplasmic face of the plasma membrane. In the eggs ofLymnaea it was found only in the vegetal hemisphere, whereas inBithynia eggs it was localized both in the vegetal hemisphere and at the animal pole. This pattern of enzyme activity corresponds to the polar pattern of transcellular ionic currents measured with the vibrating probe, which we showed to be partially carried or regulated by calcium [Zivkovic and Dohmen (1989) Biol Bull (Woods Hole) 176 (Suppl):103–109]. The characteristics of the ATPase were studied using a variety of approaches such as ion and substrate depletions and substitutions, addition of specific inhibitors of ATPase activity, treatment with EDTA/EGTA and electron energy-loss spectrometry. The results indicate that, inLymnaea, there are at least two enzymatic entities. The first one is a Ca2+ /Mg2+ ATPase localized along the membrane and in the cortex of the vegetal hemisphere. The second one is a Ca2+-stimulated ATPase (calcium pump of the plasma membrane) localized in a small region of the membrane at the vegetal pole. We speculate that in the eggs ofLymnaea andBithynia a functional relationship exists between the plasma-membrane-associated ATPase activity and the transcellular ionic currents measured in the same region.
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    URL: http://dx.doi.org/10.1007/BF01681486
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  • 93
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    Influence of altered phospholipid composition of the membrane outer layer on red blood cell aggregation: relation to shape changes and glycocalyx structure (1990)
    Springer
    European biophysics journal 18 (1990), S. 93-99 
    Details
    ISSN: 1432-1017
    Keywords: Erythrocytes ; Aggregation ; Phospholipid ; Calcium ; Red cell shape
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Reversible aggregation of erythrocytes was investigated after alteration of the phospholipid content in the membrane outer leaflet either by disturbance of endogenous transmembrane lipid asymmetry through changes in cellular free calcium, or by incorporation of exogenous lyso-derivatives. It was found that both calcium loading and lyso-phosphatidylcholine (LPC) addition induce a strong increase in red cell-red cell adhesive energy, whereas lyso-phosphatidylserine (LPS), added in the same amount as LPC, does not. Red cell morphological studies show differences in the shape change efficiency of LPS, LPC and calcium loading. However, it was further demonstrated that shape change is not directly responsible for the observed adhesive energy increase, since neuraminidase or trypsin treatment abolish this increase, even though the shape changes induced by alteration of phospholipid organization are not affected. The latter experiment strongly suggests that the red cell adhesive energy increase results from an alteration of the glycocalyx structure, which could be in turn a consequence of the shape change.
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    URL: http://dx.doi.org/10.1007/BF00183268
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    The role of magnesium and calcium ions in the glucose dehydrogenase activity of Klebsiella pneumoniae NCTC 418 (1990)
    Springer
    Archives of microbiology 153 (1990), S. 502-505 
    Details
    ISSN: 1432-072X
    Keywords: Klebsiella pneumoniae ; Chemostat culture ; Glucose metabolism ; Glucose dehydrogenase ; Pyrroloquinoline quinone ; Magnesium ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Magnesium-limited chemostat cultures of Klebsiella pneumoniae NCTC 418 with 20 μM CaCl2 in the medium showed a low rate of gluconate plus 2-ketogluconate production relative to potassium- or phosphate-limited cultures. However, when the medium concentration of CaCl2 was increased to 1 mM, the glucose dehydrogenase (GDH) activities also increased and became similar to those observed in potassium- or phosphate limited cultures. It is concluded that this is due to Mg2+ and Ca2+ ions being involved in the binding of pyrroloquinoline quinone (PQQ) to the GDH apoenzyme. There seems to be an absolute requirement of divalent cations for proper enzyme functioning and in this respect Ca2+ ions could replace Mg2+ ions. The high GDH activity which has been found in cells grown under Mg2−-limited conditions in the presence of higher concentrations of Ca2+ ions, is compatible with the earlier proposal that GDH functions as an auxiliary energy generating system involved in the maintenance of high transmembrane ion gradients.
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    URL: http://dx.doi.org/10.1007/BF00248434
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    Regulation of photosynthetic sucrose synthesis: a role for calcium? (1990)
    Springer
    Planta 182 (1990), S. 236-243 
    Details
    ISSN: 1432-2048
    Keywords: Calcium ; Partitioning ; Photosynthesis ; Sucrose synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have investigated whether changes of the cytosolic free-calcium concentration could regulate photosynthetic sucrose synthesis. Partially purified enzymes from spinach (Spinacea oleracea L.) leaves were assayed using calcium-EGTA buffers to obtain defined free-calcium concentrations in the low micromolar and submicromolar ranges. These concentrations of calcium did not directly affect sucrose-phosphate synthase activity. They inhibited the cytosolic fructose-1,6-bisphosphatase, acting competitively to magnesium. The Ki for calcium (1.2 μM) was 400-fold lower than the Km for magnesium. To investigate the in-vivo significance of these observations, the Ca2+ antagonists lanthanum (La3+), trifluoperazine, and ruthenium red were supplied to barley leaves via the transpiration stream. All three antagonists selectively inhibited sucrose synthesis: they inhibited 14C incorporation into sucrose at concentrations which did not affect starch synthesis; in low light, partitioning was changed towards starch without altering the rate of photosynthesis; there was a characteristic change in the induction kinetics of photosynthesis; and there was an accumulation of phosphorylated metabolites in the leaf. The detailed changes in metabolite levels indicate that La3+ was acting via inhibition of the fructose-1,6-bisphosphatase, trifluoperazine via blockage of the turnover of inorganic pyrophosphate, and ruthenium red via changes in the activation state (phosphorylation) of sucrose-phosphate synthase. The results are discussed in terms of a possible contribution of calcium to the regulation of carbon metabolism.
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    URL: http://dx.doi.org/10.1007/BF00197117
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    Calcium-loaded 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid blocks cell-to-cell diffusion of carboxyfluorescein in staminal hairs of Setcreasea purpurea (1990)
    Springer
    Planta 182 (1990), S. 34-38 
    Details
    ISSN: 1432-2048
    Keywords: Setcreasea ; Calcium ; Cell-to-cell communication ; Plasmodesma ; Transport, intercellular
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of microinjected calcium-loaded 1,2-bis(2-aminophenoxy) ethane-N,N,N′,N′-tetraacetic acid (CaBAPTA) on cell-to-cell diffusion of carboxyfluorescein (CF) was examined in staminal hairs of S. purpurea Boom. The CaBAPTA was microinjected into the cytoplasm of the staminal hairs either with CF or prior to a subsequent microinjection of CF. The cell-to-cell diffusion of CF along the hair was monitored using enhanced-fluorescence video microscopy. Cytoplasmic streaming stopped in cells treated with CaBAPTA, indicating that intracellular Ca2+ had increased. Cell-to-cell diffusion of CF was blocked in cells treated with Ca-BAPTA. An inhibition of cytoplasmic streaming and cell-to-cell diffusion was observed in the cells adjoining the CaBAPTA-microinjected cell, indicating that the Ca-BAPTA appeared to pass through plasmodesmata. While cytoplasmic streaming resumed 5–10 min after CaBAPTA treatment, cell-to-cell diffusion did not resume until 30–120 min later. These data support an involvement of calcium in the regulation of cell-to-cell communication in plants.
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    URL: http://dx.doi.org/10.1007/BF00239980
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    Formation and disintegration of cisternae of the endoplasmic reticulum visualized in live cells by conventional fluorescence and confocal laser scanning microscopy: Evidence for the involvement of calcium and the cytoskeleton (1990)
    Springer
    Protoplasma 155 (1990), S. 166-175 
    Details
    ISSN: 1615-6102
    Keywords: Endoplasmic reticulum ; Calcium ; Actin filaments ; DiOC6 ; Onion epidermis cells ; Confocal laser scanning microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The influence of substances interfering with the cellular calcium distribution on the organization of the endoplasmic reticulum has been investigated in live epidermal cells of onion bulb scales. The endoplasmic reticulum was visualized by vital staining with the fluorochrome DiOC6(3). It constitutes in these cells an anastomosing membrane system which is composed of three forms: cisternae, short tubules forming a peripheral network, and long tubular strands deeper in the cytoplasm. In the presence of all tested calcium interfering substances, e.g. the ionophore calcimycin (5 μM), the cryptate 221 (0.5 mM), the calmodulin antagonist calmidazolium (10 μM), the tubular ER elements disappear and huge cisternae form instead. The potassium-selective cryptate 222 (1 mM) chemically very similar to the effective cryptate 221 does not cause this change in ER pattern. Actin filaments which are indispensable for ER distribution in the epidermis cells appear to fragment in the presence of the drugs indicating some similarity with the action of cytochalasin D (Quader et al. 1989). Removal of the drugs initiates a characteristic sequence of recovery. The cisternae disintegrate at their edges into tubular loops which are pulled away from this cellular site as long tubular strands. In the presence of cytochalasin D (2 μM) the disintegration of the cisternae is inhibited indicating that kinetic forces are necessary to generate and maintain the spatial distribution of at least parts of the tubular ER meshwork. For the first time the decay of cisternae is described in live cells. The effect of the calcium agents is also compared with changes in ER organization caused by other chemical or natural means.
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    URL: http://dx.doi.org/10.1007/BF01322626
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    Caffeine inhibition of cytokinesis: Ultrastructure of cell plate formation/degradation (1990)
    Springer
    Protoplasma 157 (1990), S. 182-192 
    Details
    ISSN: 1615-6102
    Keywords: Caffeine ; Cell plate ; Phragmoplast ; Endoplasmic reticulum ; Golgi vesicles ; Microtubules ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Caffeine is a potent inhibitor of cell plate formation in dividing plant cells. Previous studies living cells reveal that the drug always permits the cell plate to arise and grow normally until about 80% complete, but then causes it to break down. In the present investigation we examine this formation/degradation cycle at the ultrastructure level. Our results show that during the formation phase the caffeine treated plate is indistinguishable from untreated controls. Phragmoplast microtubules arise and align in the interzone, Golgi vesicles are produced and aggregate in a line that defines the young cell plate, and considerable fusion of these vesicles occurs to form islands of plate material. However, under the influence of caffeine these islands do not fuse to form the enlarged lamellar expanses characteristic of maturing cell plates. Instead, the partially fused material reverts to small vesicles which appear to become resorbed by the cellular membrane systems. The resorption process continues leaving no evidence of the previously developing plate, although occasionally we observe a stub of fused vesicles attached to the parent wall. Following cell plate disintegration the reformed nuclei move close together and occupy the central region of the cell. These observations focus attention on the consolidation phase of cell plate formation as the one being maximally affected by caffeine.
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    URL: http://dx.doi.org/10.1007/BF01322651
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    The effect of organic calcium channel modulators on the germination ofVaucheria longicaulis aplanospores (1990)
    Springer
    Protoplasma 158 (1990), S. 182-190 
    Details
    ISSN: 1615-6102
    Keywords: Aplanospores ; Calcium ; Ca-channels ; Germination ; Vaucheria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary InVaucheria longicaulis var.macounii aplanospore germination and filament growth are severely inhibited by the Ca2+-channel antagonists (−)202–791, diltiazem, nifedipine and verapamil, whereas the agonists (+)202–791, Bay K-8644 and CGP-28392 stimulate those processes. Both antagonist and agonist actions suggest that voltage-controlled Ca2+ influx plays a major role in the regulation of the initial events of germination and filament growth. Increases in45Ca2+ influx are observed after pretreatment of the aplanospores with low temperature shocks of brief duration or FCCP. Both agents are known to depolarize the surface membrane.45Ca2+ influx is reduced in material treated with FC, an agent known to hyperpolarize cell membranes. The results indicate that Ca2+ influx takes place through voltage-sensitive Ca-channels.
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    URL: http://dx.doi.org/10.1007/BF01323131
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    Endoplasmic reticulum, calciosomes and their possible roles in signal transduction (1990)
    Springer
    Protoplasma 154 (1990), S. 172-178 
    Details
    ISSN: 1615-6102
    Keywords: Cell motility ; Endoplasmic reticulum ; Calcium ; Calciosomes ; Acetabularia ; Inositol phosphate ; Signal transduction ; Intracellular particle motions ; Actin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Recent fluorescence, AVEC-DIC, and confocal laser scanning microscopic studies have revealed the dynamic nature and structural extent of a calcium-sequestering endoplasmic reticulum (ER) in plant cells. Various investigators have proposed different roles for the ER in cell motility. One, the ER plays a direct role in the generation of intracellular particle motions or two, the ER regulates particle motions indirectly. We show that the ER can be extruded fromAcetabularia cells, stains brightly with the fluorescent dye DiOC6(3), and small (ca. 100 nm diameter) fluorescent vesicles are observed to move in or along the ER tubules. Intracellular particle movements in the giant algal cellAcetabularia can be transiently inhibited by IP4, IP3, and IP2, compounds which in animal cells are known to cause the release of free calcium ions. A model is proposed which clarifies the possible relationships between the ER, calciosomes, calcium ions, and the microfilament-generated intracellular particle movements observed in plant cells.
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    URL: http://dx.doi.org/10.1007/BF01539845
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