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1.
André B. Borle Takashi Uchikawa Julius H. Anderson 《The Journal of membrane biology》1982,68(1):37-46
Summary Stimulations or inhibitions by various agents of45Ca efflux from prelabeled cells or tissues display distinct and reproducible profile patterns when the results are plotted against time as fractional efflux ratios (FER). FER is the fractional efflux of45Ca from stimulated cells divided by the fractional efflux from a control unstimulated group. These profile patterns fall into three categories: peak patterns, exponential patterns, and mixed patterns. Each category can be positive (stimulation) or negative (inhibition). The interpretation of these profiles is difficult because45Ca efflux depends on three variables: the rate of calcium transport out of the cell, the specific activity of the cell compartment from which the calcium originates, and the concentration of free calcium in this compartment. A computer model based on data obtained by kinetic analyses of45Ca desaturation curves and consisting of two distinct intracellular pools was designed to follow the concentration of the traced substance (40Ca), the tracer (45Ca), and the specific activity of each compartment before, during, and after the stimulation or the inhibition of calcium fluxes at various pool boundaries. The computer model can reproduce all the FER profiles obtained experimentally and bring information which may be helpful to the interpretation of this type of data. Some predictions of the model were tested experimentally, and the results support the views that a peak pattern may reflect a sustained change in calcium transport across the plasma membrane, that an exponential pattern arises from calcium mobilization from an internal subcellular pool, and that a mixed pattern may be caused by a simultaneous change in calcium fluxes at both compartment boundaries. 相似文献
2.
Gregory J. Barritt 《The Journal of membrane biology》1981,62(1-2):53-63
Summary The distribution of calcium between isolated rat liver mitochondria and the extramitochondrial medium at 37°C and in the presence of 2mm inorganic phosphate, 3mm ATP, 0.05 or 1.1mm free magnesium and a calcium buffer, nitrilotriacetic acid, was investigated using a45Ca exchange technique. The amounts of40Ca in the mitochondria and medium were allowed to reach equilibrium before initiation of the measurement of45Ca exchange. At 0.05mm free magnesium and initial extramitochondrial free calcium concentrations of between 0.15 and 0.5 m, the mitochondria accumulated calcium until the extramitochondrial free calcium concentration was reduced to 0.15 m. Control experiments showed that the mitochondria were stable under the incubation conditions employed. The45Ca exchange data were found to be consistent with a system in which two compartments of exchangeable calcium are associated with the mitochondria. Changes in the concentration of inorganic phosphate did not significantly affect the45Ca exchange curves, whereas an increase in the concentration of free magnesium inhibited exchange. The maximum rate of calcium outflow from the mitochondria was estimated to be 1.7 nmol/min per mg of protein, and the value ofK
0.5 for intramitochondrial exchangeable calcium to be about 1.6 nmol per mg of protein. Ruthenium Red decreased the fractional transfer rate for calcium inflow to the mitochondria while nupercaine affected principally the fractional transfer rates for the transfer of calcium between the two mitochondrial compartments. The use of the incubation conditions and45Ca exchange technique described in this report for studies of the effects of agents which may alter mitochondrial calcium uptake or release (e.g., the pre-treatment of cells with hormones) is briefly discussed. 相似文献
3.
André B. Borle 《The Journal of membrane biology》1982,66(1):183-191
Summary The influence of extracellular Na (Na
o
) on cellular Ca transport and distribution was studied in rat kidney slices. Calcium efflux from prelabeled slices was depressed when Na
o
was completely replaced by choline or tetraethylammonium (TEA) ions and it was markedly stimulated when Na was reintroduced in a Na-free medium. However, reducing Na
o
(with choline or TEA as substituting ions) did not increase the total slice40Ca, their total exchangeable Ca pool, or the40Ca or45Ca of mitochondria isolated from these slices. Kinetic analyses of steady-state45Ca desaturation curves showed that reducing Na
o
depressed the exchange of Ca across the plasma membrane, slightly decreased the cytosolic Ca pool, but did not significantly affect the mitochondrial Ca pool and Ca cycling. Ouabain (10–3
m) which should reduce the Na gradient across the plasma membrane had no effect on calcium distribution and transport. These results suggest that in kidney cells low Na
o
depresses Ca influx as well as Ca efflux; there may be an interaction between Na and Ca at a possible carrier located in the plasma membrane, but there is no Na/Ca exchange as described in several excitable tissues. 相似文献
4.
The acute effect of a hypoglycaemic dose of 0.5 U/100 g BW insulin administered intramuscularly on calcium metabolism was investigated in fasted alloxan-treated rats. It was found that the hypercalcaemic effect of insulin was evident only in thyroparathyroidectomized (TPTX) and not in parathyroidectomized (PTX) rats. A subcutaneous administration of 180 MRC mU/100 g BW calcitonin abolished the calcium raising effect of insulin in TPTX rats suggesting a protective role of calcitonin against insulin action in intact rats. In an attempt to elucidate the mechanism of the calcium raising effect of insulin 45Ca administered intravenously was used to indicate the movement of calcium from the plasma pool. Insulin administration delayed the plasma 45Ca disappearance rate but had no effect on bone 45Ca uptake within 120 min. In contrast, insulin administration resulted in a 31% reduction of urinary 45Ca excretion while the urine volume remained unchanged. However, the insulin-induced reduction of urinary calcium excretion could not totally account for the calcium raising effect of insulin in TPTX animals. 相似文献
5.
A. Herchuelz P. Lebrun A. Carpinelli N. Thonnart A. Sener W.J. Malaisse 《生物化学与生物物理学报:生物膜》1981,640(1):16-30
The effects of quinine and 9-aminoacridine, two blockers of potassium conductance in islet cells, on 45Ca efflux and insulin release from perifused islets were investigated in order to elucidate the mechanisms by which glucose initially reduces 45Ca efflux and later stimulates calcium inflow in islet cells. In the absence of glucose, 100 μM quinine stimulated 45Ca net uptake, 45Ca outflow rate and insulin release. Quinine also dramatically enhanced the cationic and the secretory response to intermediate concentrations of glucose, but had little effect on 45Ca net uptake, 45Ca fractional outflow rate and insulin release at a high glucose concentration (16.7 mM). The ability of quinine to stimulate 45Ca efflux depended on the presence of extracellular calcium, suggesting that it reflects a stimulation of calcium entry in the islet cells. In the absence of extracellular calcium, quinine provoked a sustained decrease in 45Ca efflux. Such an inhibitory effect was not additive to that of glucose, and was reduced at low extracellular Na+ concentration. At a low concentration (5 μM), quinine, although reducing 86Rb efflux from the islets to the same extent as a non-insulinotropic glucose concentration (4.4 mM), failed to inhibit 45Ca efflux. In the presence of extracellular calcium, 9-aminoacridine produced an important but transient increase in 45Ca outflow rate and insulin release from islets perifused in the absence of glucose. In the absence of extracellular calcium, 9-aminoacridine, however, failed to reduced 45Ca efflux from perifused islets. It is concluded that quinine, by reducing K+ conductance, reproduces the effect of glucose to activate voltage-sensitive calcium channels and to stimulate the entry of calcium into the B-cell. However, the glucose-induced inhibition of calcium outflow rate, which may also participate in the intracellular accumulation of calcium, does not appear to be mediated by changes in K+ conductance. 相似文献
6.
《Bone and mineral》1990,8(3):185-193
Two experiments were undertaken to study the abilities of clomiphene citrate (20 mg/kg body wt/wk s.c.) and tamoxifen citrate (20 mg/kg body wt/wk s.c.) to slow bone resorption mediated by (a) endogenous parathyroid hormone (PTH) and (b) exogenous calcitriol (1,25(OH)2D3) in vivo in rats with intact ovarian function. Groups of rats with 45Ca-labelled bones were fed a low-calcium (0.01% Ca) diet to stimulate secretion of PTH. Neither clomiphene nor tamoxifen slowed the mobilization of 45Ca from femoral bone or prevented the reduction in bone calcium induced by feeding this diet. Moreover these drugs did not depress the urinary excretion of 45Ca or hydroxyproline. These observations indicated that clomiphene and tamoxifen did not inhibit PTH-mediated bone resorption. Administering calcitriol (50 ng/day) orally for 14 days raised plasma calcium, increased urinary 45Ca and its specific activity and decreased femur 45Ca: all these responses were similar in animal, receiving calcitriol alone and calcitriol with clomiphene or tamoxifen. The femur 45Ca values (dpm × 10−3) were: (means ± SD, n = 8) placebo, 1901 ± 127; 1,25(OH)2D3, 1727 ± 967; clomiphene + 1,25(OH)2D3, 1694 ± 937; tamoxifen + 1,25(OH)2D3, 1664 ± 617. (7 = P < 0.01). Thus neither clomiphene nor tamoxifen prevented calcitriol-mediated bone resorption in vivo in the rat. 相似文献
7.
Computer simulation of calcium homeostasis in chicks predicted an oscillatory behavior of bone calcium flow and kidney 25-hydroxyvitamin D3-1 hydroxylase with a periodicity of 56 h and a 9 h phase difference between the two signals. In growing chickens subjected to a light: dark cycle of 22:2 h, and intravenously dosed with 45Ca, the temporal changes in plasma 45Ca could be described by an exponential decline with superimposed diurnal oscillations. The activity of the renal 25-hydpoxyvitamil D3-1-hydroxylase in chicks subjected to a 12:12 h light: dark cycle ALSO followed diupnal oscillations, with a ladir at the beginning of the light period and a peak 12 h later. The production of 1,25-dihydroxyvitamin D3 by primary cultures of chicken kidney cells mscillated with a periodicity of 5.6 h or shorter. It is suggested that despite the differences in phase and periodicity between the simulation predictions and actual results, the oscillations in both 1-hydroxylase and bone calcium flow could be coupled through the hormonal systems involved in regulation of plasma calcium. 相似文献
8.
《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1995,110(1):23-28
Eggshell formation and egg production in domestic fowl were studied following the administration of methyl mercury (two dose regimes: 5 mg daily for 6 consecutive days and 1 mg daily for 50 consecutive days). A daily oral dose of 5 mg of methyl mercury for 6 consecutive days induced significant eggshell thinning and deformation and inhibited egg production. Uptake of 45Ca and synthesis of prostaglandins by a homogenate of eggshell gland mucosa from methyl-mercury-treated birds were significantly reduced, as was the calcium content of blood plasma. A daily oral dose of 1 mg of methyl mercury administered for 50 consecutive days also induced eggshell deformation and thinning and reduced egg production. This dose did not, however, have significant effects on the following: 45Ca uptake and prostaglandin synthesis by a homogenate of the eggshell gland mucosa; 45Ca uptake by a homogenate of duodenal mucosa; the Ca content of the blood plasma, shell gland mucosa or shell gland lumen; the HCO3− content of the shell gland lumen or the specific gravity of tibia. Methyl mercury added in vitro to a homogenate of eggshell gland mucosa significantly stimulated the synthesis of prostaglandins PGF2α and PGE2. Addition of mercury chloride to the same type of preparation stimulated the synthesis of PGF2α at the expense of thromboxane (T × B2) synthesis. Administration of 5 mg methyl mercury for 6 consecutive days seemed to reduce the availability of calcium for eggshell formation. This effect could have been due to a direct inhibitory effect of methyl mercury on calcium uptake from the gastrointestinal tract and/or to mobilization of medullary bone. The administration of 1 mg methyl mercury for 50 consecutive days probably induced the reproductive effects by another mechanism. The effects of methyl mercury on avian eggshell formation are quite different from the effects p,p′-DDE exerts on that process. 相似文献
9.
Primary cultures of bone cells and skin fibroblasts were examined for their Ca++ content, intracellular distribution and Ca++ fluxes. Kinetic analysis of 45Ca++ efflux curves indicated the presence of three exchangeable Ca++ compartments which turned over at different rates: a “very fast turnover” (S1), a “fast turnover” (S2), and a “slow turnover” Ca++ pool (S3). S1 was taken to represent extracellular membrane-bound Ca++, S2 represented cytosolic Ca++, and S3 was taken to represent Ca++ sequestered in some intracellular organelles, probably the mitochondria. Bone cells contained about twice the amount of Ca++ as compared with cultured fibroblasts. Most of this extra Ca++ was localized in the “slow turnover” intracellular Ca++ pool (S3). Serum activation caused the following changes in the amount, distribution, and fluxes of Ca++: (1) In both types of cells serum caused an increase in the amount of Ca++ in the “very fast turnover” Ca++ pool, and an increase in the rate constant of 45Ca++ efflux from this pool, indicating a decrease in the strength of Ca++ binding to ligands on cell membranes. (2) In fibroblasts, serum activation also caused a marked decrease in the content of Ca++ in the “slow turnover” Ca++ pool (S3), an increase in the rates of Ca++ efflux from the cells to the medium, and from S3 to S2, as well as a decrease in the rate of influx into S3. (3) In bone cells the amount of Ca++ in S3 remained high in “serum activated” cells, the rate of efflux from S3 to S2 increased, and the rate of influx into S3 also increased. The rate of efflux from the cells to the medium did not change. The results suggest specific properties of bone cells with regard to cell Ca++ presumably connected with their differentiation. Following serum activation we investigated the time course of changes in the amount of exchangeable Ca++ in bone cells and fibroblasts, in parallel with measurements of 3H-thymidine incorporation and cell numbers. Serum activation caused a rapid decrease in the content of cell Ca++ which was followed by a biphasic increase lasting until cell division. 相似文献
10.
R. I. Sha'Afi P. H. Naccache T. Alobaidi T. F. P. Molski M. Volpi 《Journal of cellular physiology》1981,106(2):215-223
A detailed examination of the effects of exogenous arachidonate on cation metabolism in rabbit neutrophils was undertaken. Arachidonic acid stimulates the movement of 45Ca into and out of the neutrophils with a net result, in the presence of extracellular calcium, of increasing the steady-state level of 45Ca. Arachidonate also increases the uptake of 22Na. These effects of arachidonate are specific to these cations, concentration-dependent, and sensitive to lipoxygenase inhibitors. At the concentrations used in this study arachidonate does not influence the permeability of human erythrocytes to 45Ca. Furthermore, both arachidonic acid and F-Met-Leu-Phe release calcium from a previously unexchangeable intracellular pool and the effect of the two stimuli are not additive. Arachidonic acid-dependent, but not F-Met-Leu-Phe-dependent, calcium release is sensitive to lipoxygenase inhibitors. These two stimuli thus appear to release is sensitive to lipoxygenase inhibitors. These two stimuli thus appear to release calcium from the same pool(s) by separate mechanisms. The results summarized above are consistent with the hypothesis that one or more arachidonate metabolites are involved in the mechanism underlying the chemotactic factor induced permeability changes in rabbit neutrophils. 相似文献
11.
Summary Calcium in the myocardial cell is highly compartmentalized and a fast, an intermediate, a slow and a nonexchangeable calcium pool have been described. The fast pool contains 66% of the total cell exchangeable calcium in cultured neonatal rat heart cells with a t
1/2 of < 1.5 sec. Though the cellular origin of this fast pool is unknown, its rapidity and its displacement by La3+ most likely places it at the sarcolemma or at least in rapid equilibrium with the sarcolemma.We isolated the sarcolemma of cultured neonatal rat heart cells using the gas-dissection technique, which yields a pure sarcolemmal preparation in less than a second, thereby precluding membrane changes which might occur during conventional plasma membrane isolation. We determined the calcium binding characteristics of these membranes, using an on-line technique to monitor 45Ca, which allows measurement of 45Ca binding characteristics in the presence of unbound 45Ca. Two classes of calcium binding sites were determined: (i) K
d
of 13 m, capacity 7 nmol/mg and (ii) K
d of 1.1 mm, capacity of 84 nmol/mg. To assess the molecular origin of the sarcolemmal calcium binding we treated the membranes with a variety of enzymes. Protease or neuraminidase treatment did not cause large changes in these parameters. Simultaneous treatment with two different phospholipases C or the extraction of the lipids with isopropanol resulted in a dramatic loss of the low-affinity binding sites.These results, in association with previously defined sarcolemmal phospholipid distribution, places the low-affinity binding sites at the cytoplasmic leaflet. The physiological implication of this localization as it pertains to cellular calcium exchange is discussed.We thank Eloise Andrews-Farley for culturing of the neonatal cells. This study is supported by U.S. Public Health Service grants HL 28539-07 and 08, the Laubisch Fund, the Castera Foundation and the American Heart Association, Greater Los Angeles Affiliate. 相似文献
12.
The Action of Serotonin on Calcium-45 Efflux from the Anterior Byssal Retractor Muscle of Mytilus edulis
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45Ca efflux was studied in resting anterior byssal retractor muscle. The data are described by a three-compartment system. The most rapidly exchanging compartment, with an average time constant of 7 min, contains about 0.9 mM Ca/liter muscle, and probably represents extracellular space. A second compartment, with a time constant of 83 ± 5 min, contains 1.2 mM Ca/liter, and may represent a membrane calcium store. The presence of a third, or more, compartments, probably representing sarcoplasmic reticulum and contractile proteins, is indicated by the fact that the final time constant is 10 times the 83 min time constant of the second compartment. Serotonin (5HT), on initial application, increases 45Ca efflux from this third compartment(s). This effect has a typical dose-response relationship with a maximum response appearing at 10-7
M5HT. In addition, removal of 5HT causes a secondary increase in 45Ca efflux which has a maximum at a 5HT concentration of 10-7
M and declines at both higher and lower doses. 相似文献
13.
The efflux kinetics of45Ca from rat brain cortex thin slices previously equilibrated with it, was studied in a superfusion system. Two first order kinetic components of efflux from the tissue were found: k2=0.0667 min–1, that was unchanged by lowering the temperature from 37°C to 15°, and k3=0.0167 min–1 at 37°C, that was reduced to 0.0897 min–1 at 15°C. This suggests that k2 represents efflux from the extracellular space, and k3 that from the cellular compartment. Addition of the mitochondrial uncoupler carbonyl cyanide,m-chlorophenylhydrazone (CCCP) (10–5 M) increased the efflux fractional rate constant of45Ca by 35%, while no change in efflux was induced by 10 mM caffeine. Veratridine (10–5M) drastically reduced45Ca efflux if superfusion was with physiological salt solution (150 mM sodium present), but not if 50 mM lithium replaced an equivalent amount of sodium in the superfusion fluid. This lithium-containing solution did not affect45Ca efflux in the absence of veratridine. These results indicate that mitochondria accumulate only a minor fraction of intracellular45Ca; that45Ca possibly turns over very rapidly in the endoplasmic reticulum, and that most of45Ca is present in a different, non-mitochondrial, non endoplasmic reticular compartment, the nature of which can be only conjectured. 相似文献
14.
《Biochimica et Biophysica Acta (BBA)/General Subjects》1986,881(3):383-390
Binding of [3H]aflatoxin B1 to rat plasma was investigated in vivo and vn vitro. Column chromatographic and polyacrylamide gel electrophoretic analysis clearly demonstrated that aflatoxin B1 bound primarily plasma albumin. Very little binding activity was shown by other plasma proteins. Spectrofluorimetric studies were undertaken to gain some insight into the nature of the aflatoxin-albumin interaction. Quenching of the lone tryptophan fluorescence intensity upon aflatoxin binding was due, at least in part, to a ligand-induced conformational change in the albumin molecule. Aflatoxin B1 binds an apolar site with an association constant of 30 mM−1 at pH 7.4 and 20°C. Neither charcoal treatment of rat albumin nor the presence of 0.15 M NaCl had many significant effect on the interaction. The association constant was pH-dependent, increasing about 1.7-fold as the pH increased from 6.1 to 8.4. This pH dependence is ascribed to a pH-induced conformational change in the albumin molecule. Thermodynamic studies indicated that the aflatoxin-albumin interaction was exothermic (ΔH = −29.3 kJ·mol−), with a ΔS value of −13.8 J·mol−1·K−1. 相似文献
15.
Relationship between bisphosphonate concentration and osteoclast activity and viability 总被引:1,自引:0,他引:1
Dorothy J. Rowe Lois A. Etre Michael J. Lovdahl Donald J. Pietrzyk 《In vitro cellular & developmental biology. Animal》1999,35(7):383-388
Summary Difluoromethylidene bisphosphonate (F2MBP) is one of the many bisphosphonates known to inhibit bone resorption in vitro and in vivo. We have developed an analytical
method, employing anion exchange and postcolumn indirect fluorescence detection, by which F2MBP can be quantified in bone samples. The objective of this study was to relate the concentration of F2MBP in embryonic bones treated in organ culture to the physiological effects of the compound, such as bone resorption (i.e.,
the amount of 45Ca released into the medium from prelabeled bones) and viability of the osteoclast population (i.e., the incidence of abnormal
osteoclasts). Osteoclasts in bones treated with F2MBP exhibited morphological features of apoptosis, such as nuclear fragmentation. Both the number and percentage of these
abnormal cells increased with dose of F2MBP and duration of incubation. The decrease in normal osteoclasts was correlated with the decreased amount of 45Ca released into the medium. Bones treated with F2MBP for only the first 5 min of the 48-h incubation period had similar numbers of abnormal osteoclasts and amounts of 45Ca released, as had bones incubated with F2MBP continuously for 48 h. The uptake of F2MBP into the bone was rapid. Bones treated with F2MBP for 6 h were similar to bones treated with F2MBP for the entire 48-h incubation period, both in F2MBP concentration and the 45Ca release ratios. These relationships between concentrations of F2MBP within bone and osteoclast activity and viability implicate apoptosis in the mechanism by which this bisphosphonate inhibits
bone resorption. 相似文献
16.
J. David Malone Arnold J. Kahn Steven L. Teitelbaum 《Biochemical and biophysical research communications》1982,108(2):468-473
A prevailing concept in the literature on bone resorption suggests that the removal of calcium crystals from the bone matrix is the result of the secretion of lactic and/or citric acid. In the present study, we have reassessed this concept using an in vitro bone resorption system consisting of thioglycolate elicited rat peritoneal macrophages co-cultured, for up to 96 hours, with devitalized 45Ca-labeled bone particles. In these combined cultures, medium lactate concentration increased linearly for the first 48 hours of culture and remained at a plateau thereafter. Medium citrate concentration, on the other hand, remained constant and at very low levels throughout incubation. In contrast to both citrate and lactate, bone resorption, measured as 45Ca release, began a few hours after the onset of culture and increased at a constant rate for the balance of the 96-hour culture period. Alteration of resorptive activity by the addition of 10?6M cortisol (which stimulates 45Ca release) or the interposition of a filter between cells and bone (which inhibits resorption) was not paralleled by similar shifts in lactate or citrate concentration. These experiments indicate that mobilization of the bone mineral can occur in the absence of a concurrent, generalized release of lactic and citric acid by sesorbing cells. On the other hand, the data do not exclude a possible role for these compounds under circumstances where they are secreteo into a “closed” compartment at the cell-bone interface or, in the case of lactate, during the initial period of resorptive activity. 相似文献
17.
Seiji Ichida Naruhisa Matsuda Satori Nakazaki Hiroyuki Kishino Tetsuyuki Wada Takafumi Akimoto 《Neurochemical research》1993,18(5):625-632
The characteristics of KCl-stimulated45Ca uptake by neuroblastoma x glioma hybrid NG108-15 cells induced to differentiate with dibutyryl cAMP (Bt2cAMP) and of PC12h pheochromocytoma cells induced to differentiate with nerve growth factor (NGF) were studied. The extent and rate of KCl-stimulated45Ca uptake by differentiated NG108-15 cells induced with Bt2cAMP were significantly higher than those of the undifferentiated cells. However, differentiation of PC12h cells induced with NGF did not enhance their extent or rate of KCl-stimulated45Ca uptake. The effects of Ca agonist and antagonists indicated that the characteristics of KCl-stimulated45Ca uptake by Bt2cAMP-treated NG108-15 cells and NGF-treated PC12h cells mainly reflected those of peripheral L-type voltage-sensitive calcium channels activated by high KCl. These results suggest that differentiated neural cells did not all show an enhanced capacity for KCl-stimulated45Ca uptake, although the characteristic patterns of differentiation (extension of neurite-like processes, etc.) and that of effect by Ca agonist or antagonists on NG108-15 cells and PC12h cells were similar. 相似文献
18.
J. E. Brehe W. R. Fleming 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1976,110(2):159-169
1. | Seasonal changes in the half-times (0.5) for calcium influx and outflux in bone, skin and scales, and soft-tissue compartments ofF. kansae were measured. |
2. | The size of diffusible calcium pools in the three compartments was estimated from the ratio of the loading and unloading half-times. Both the bone and skin and scales compartments contain diffusible calcium pools which increase in size during the summer months. |
3. | The calcium in the soft-tissue compartment is all diffusible, and the kinetics indicate that this compartment receives calcium from the other two compartments. |
4. | Hypophysectomy reduced the rate of calcium turnover in summer animals to the levels measured in intact winter animals. Such treatment also affected the distribution of radiocalcium within the animal. |
5. | It is concluded that acellular bone is a metabolically active tissue. |
19.
Jean-Denis Troadec Sylvie Thirion Jean-Pierre Laugier Ghislain Nicaise 《Biology of the cell / under the auspices of the European Cell Biology Organization》1998,90(4):339-347
Digitonin-permeabilized isolated neurohypophysial nerve terminals are known to release their secretory vesicle content under calcium challenge. On this preparation, we monitored intra-organelle Ca2+ concentration using digital fluorescence microscopy of Fura-2. The superfusion of artificial intracellular solution containing 10 to 50 μM Ca2+ induced an intra-organelle [Ca2+] increase. Two major organelles are candidates for this increase: secretory vesicles and mitochondria. In an attempt to detect calcium changes in the vesicles, ruthenium red was used to impair mitochondrial calcium uptake. Part of the ruthenium red-insensitive intra-organelle [Ca2+] increase was abolished by raising sodium in the solution. Removing sodium boosted the intra-organelle [Ca2+] increase. These results taken together suggest the participation of Na/Ca exchange, known to exist in the membrane of these secretory vesicles. In addition to Na/Ca exchange, there would be at least another mechanism of vesicular calcium intake, as suggested by the partial inhibition of intra-organelle [Ca2+] increase obtained under acidic compartments: neutralization with NH4Cl. This mechanism remains to be defined. The main conclusion presented here, that an intravesicular [Ca2+] increase takes place at the rate of secretion, was predicted by the hypothesis that intravesicular Ca2+ changes would be involved in stimulus-secretion coupling. 相似文献
20.
The effects of triamcinolone acetonide on the pattern of 45calcium efflux were investigated in cultured bone cells. Efflux was measured after equilibrating the cells with 45calcium for 24 hours and a short (3 hours) or a long (24 hours) preincubation with the hormone. The results were analyzed by fitting them to a model of three exponential terms, using a computer program based on the non-linear least square method. As reported previously the results indicated the presence of three exchangeable calcium pools which differ in their rates of calcium exchange. A short preincubation with the hormone (3 hours) caused the following changes: (1) A marked increase in the amount of exchangeable calcium in the “slow turnover” calcium pool (S3) which is probably in the mitochondria. (2) A lesser but significant increase in the amount of calcium in the “fast turnover” calcium pool (S2) which is probably the calcium in the cytosol. (3) An increase in the rates of calcium exchange between S2 and the medium (?20) and between S3 and S2 (?32). All these changes were transient. After 24 hours of preincubation with triamcinolone acetonide the amounts of calcium in S2 and S3 decreased below the control levels and the fluxes were not significantly different from those of the controls. 相似文献