Effects of pH on bone calcium and proton fluxes in vitro

1983 ◽  
Vol 245 (2) ◽  
pp. F204-F209 ◽  
Author(s):  
D. A. Bushinsky ◽  
N. S. Krieger ◽  
D. I. Geisser ◽  
E. B. Grossman ◽  
F. L. Coe
Keyword(s):  
Alkaline Medium ◽  
Sodium Azide ◽  
Calcium Release ◽  
Calcium Influx ◽  
Calcium Flux ◽  
Metabolic Inhibitor ◽  
Calcium Efflux ◽  
Medium Ph ◽  
Proton Fluxes

Bone mineral is thought to decompose during acute and chronic metabolic acidosis and thereby contribute to buffering of the acid load. We cultured neonatal mouse calvariae for 3 h and found calcium efflux from bone when the medium pH was below 7.40, calcium influx into bone when the pH was above 7.40, and no net flux at pH 7.40. The calcium flux varied to the same extent when medium pH was altered by a primary change in the medium bicarbonate concentration or in the partial pressure of carbon dioxide. Calcium and proton fluxes were inversely correlated (r = -0.713, P less than 0.001), and the slope of the linear regression indicated that between 16 and 21 neq of proton entered the calvariae in exchange for each neq of calcium that left. In 24-h cultures, acid medium also caused net calcium efflux from bone, and alkaline medium caused net influx. PTH increased calcium efflux at acid but not at alkaline medium pH. Sodium azide resulted in net influx of calcium into bone at all values of medium pH. Calcium release by cultured calvariae in response to low medium pH is associated with proton buffering; over 3 h the stoichiometry indicates that little buffering is due to the dissolution of calcium-containing crystals. Effects of medium pH on calcium release are amplified by PTH, and calcium efflux can be prevented by the metabolic inhibitor sodium azide.

The acute hypocalcaemic effect of ethanol and its mechanism of action in the rat

1983 ◽  
Vol 61 (4) ◽  
pp. 388-394 ◽  
Author(s):  
Nateetip Krishnamra ◽  
Liangchai Limlomwongse
Keyword(s):  
Body Weight ◽  
Mechanism Of Action ◽  
Calcium Release ◽  
Calcium Influx ◽  
Plasma Calcium ◽  
In Vitro Studies ◽  
Calcium Efflux ◽  
Plasma Pool ◽  
Suppressive Action

The hypocalcaemic action of ethanol (3 g/kg body weight) was investigated in intact, thyroparathyroidectomized and antrectomized rats. It was found that ethanol administered either intraperitoneally or orally reduced plasma calcium concentrations within 30 min and that this response lasted for 8 h. Additional studies performed in antrectomized and thyroparathyroidectomized rats indicated that neither gastrin nor the hormones parathormone and calcitonin had any effect on the hypocalcaemic effect of ethanol. Investigation of the mechanism of action of ethanol-induced hypocalcaemia involved measurements of calcium efflux from and influx into the plasma pool. Ethanol did not have any effect on the disappearance from plasma of 45Ca administered intravenously at 0 min. In contrast, ethanol was found to enhance the disappearance of 45Ca administered intraperitoneally 17 h prior to the experiment. The interpretation of 45Ca studies was discussed and it was concluded that ethanol-induced hypocalcaemia resulted from a decrease in calcium influx into the plasma. Additional in vitro studies did not indicate the suppressive action of ethanol on the release of calcium from tibias. In conclusion, our results show that the mechanism of hypocalcaemia caused by ethanol is the suppression of calcium release from some tissue(s) into the plasma.

Cellular contribution to pH-mediated calcium flux in neonatal mouse calvariae

1985 ◽  
Vol 248 (6) ◽  
pp. F785-F789 ◽  
Author(s):  
D. A. Bushinsky ◽  
J. M. Goldring ◽  
F. L. Coe
Keyword(s):  
Sodium Azide ◽  
Culture Medium ◽  
Cell Function ◽  
Bone Cell ◽  
Neonatal Mouse ◽  
Calcium Flux ◽  
Calcium Efflux ◽  
Medium Ph ◽  
Freeze Thaw ◽  
Net Flux

Net calcium flux from cultured neonatal mouse calvariae into the culture medium is pH dependent, and acidified culture medium causes egress of calcium from bone. To determine whether calcium flux is mediated by pH effects on bone cell function, we cultured calvariae for 24 h with sodium azide, acetazolamide, parathyroid hormone (PTH), 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], or after three successive freeze-thaw cycles, treatments that would be expected to alter bone cell function. We recultured bones for 3 h with the respective treatment and measured calcium flux. Sodium azide and freeze-thaw cycles produced a net influx of calcium (JCa = -22 +/- 7 and -23 +/- 6 nmol X bone-1 X 3 h-1, respectively) compared with net efflux of control bones (JCa = 35 +/- 6) at a similar initial medium pH. Acetazolamide reduced net flux to 0 (JCa = 7 +/- 6). PTH and 1,25(OH)2D3 increased net calcium efflux from bone (JCa = 78 +/- 7 and 74 +/- 10, respectively). Despite changing net flux, the slope dependence of net flux on medium pH was the same in the control group and all five treated groups of bones. The similarity of slopes indicates that the pH dependence of net flux is not a result of pH acting on bone cells but probably an effect of altered mineral equilibria. The difference in net flux at similar pH indicates that calcium efflux is partially inhibited by acetazolamide and stimulated by both PTH and 1,25(OH)2D3.

Mechanism of aluminum-induced calcium efflux from cultured neonatal mouse calvariae

1990 ◽  
Vol 258 (3) ◽  
pp. F583-F588 ◽  
Author(s):  
S. M. Sprague ◽  
D. A. Bushinsky
Keyword(s):  
Bone Mineral ◽  
Calcium Influx ◽  
Neonatal Mouse ◽  
Mineral Dissolution ◽  
Calcium Flux ◽  
Calcium Efflux ◽  
Dead Bone ◽  
45Ca Efflux ◽  
Dose Dependent

Aluminum has been shown to increase unidirectional 45Ca efflux from prelabeled bones in vitro; whether aluminum affects net calcium efflux and, if so, by what mechanism has not been studied. To examine the effects of aluminum on net calcium flux from bone we cultured live and dead neonatal mouse calvariae with and without graded concentrations of aluminum (10(-8) to 10(-5) M). Aluminum induced a dose-dependent net calcium efflux from live bone after 24 h, but not 3 h, which was similar in magnitude to that produced by 10(-8) M parathyroid hormone. The normal calcium influx into dead bone was not altered by aluminum. Release of beta-glucuronidase, a lysosomal enzyme released by osteoclasts, increased after a 24-h incubation in aluminum-containing medium and was correlated with net calcium efflux. Calcitonin, an inhibitor of osteoclastic bone mineral dissolution, abolished the increase in beta-glucuronidase release and nullified the aluminum-induced net calcium efflux. Thus aluminum induces cell-mediated net calcium efflux from bone and increases beta-glucuronidase release. Calcitonin inhibits the increase in both calcium efflux and beta-glucuronidase release, suggesting that aluminum stimulates osteoclasts to release bone mineral.

Human placental lactogen release in vitro: paradoxical effects of calcium

1981 ◽  
Vol 240 (5) ◽  
pp. E550-E555
Author(s):  
S. Handwerger ◽  
P. M. Conn ◽  
J. Barrett ◽  
S. Barry ◽  
A. Golander
Keyword(s):  
Calcium Influx ◽  
Extracellular Calcium ◽  
Calcium Flux ◽  
Placental Lactogen ◽  
Human Placental Lactogen ◽  
Paradoxical Effects ◽  
Subsequent Exposure ◽  
Normal Calcium

To study the effects of calcium on the release of human placental lactogen (hPL), placental explants were exposed to media containing lower or higher concentrations of calcium than normally available to the placenta. Explants exposed for 2 h to calcium-poor medium or medium containing either 2 mM EDTA or 2 mM EGTA released 160, 248, and 253% more hPL, respectively, than control explants. In contrast, explants exposed to medium containing higher than normal calcium concentrations released the same amounts of hPL as the control explants. At lower than normal extracellular calcium concentrations, the increased hPL release was inversely proportional to the calcium concentration. The increased release in calcium-poor medium was inhibited by subsequent exposure of the explants to medium containing calcium and was prevented by either barium or magnesium. Changes in barium or magnesium concentrations, however, had no effects on hPL release in the presence of normal extracellular calcium concentrations. Methoxyverapamil (D 600), an inhibitor of calcium flux, stimulated hPL release. Because low extracellular calcium and methoxyverapamil both inhibit calcium influx, these experiments suggest that calcium influx inhibits hPL release. The role of calcium in the regulation of hPL release therefore appears to be different from that reported in other release systems.

Metabolic alkalosis decreases bone calcium efflux by suppressing osteoclasts and stimulating osteoblasts

1996 ◽  
Vol 271 (1) ◽  
pp. F216-F222 ◽  
Author(s):  
D. A. Bushinsky
Keyword(s):  
Bone Mineral ◽  
Metabolic Alkalosis ◽  
Collagen Synthesis ◽  
Cell Function ◽  
Urinary Calcium ◽  
Calcium Excretion ◽  
Calcium Efflux ◽  
Medium Ph ◽  
Bone Calcium

In vivo and in vitro evidence indicates that metabolic acidosis, which may occur prior to complete excretion of end products of metabolism, increases urinary calcium excretion. The additional urinary calcium is almost certainly derived from bone mineral. Neutralization of this daily acid load, through the provision of base, decreases calcium excretion, suggesting that alkali may influence bone calcium accretion. To determine whether metabolic alkalosis alters net calcium efflux (JCa+) from bone and bone cell function, we cultured neonatal mouse calvariae for 48 h in either control medium (pH approximately equal to 7.4, [HCO3-] approximately equal to 24), medium simulating mild alkalosis (pH approximately equal to 7.5, [HCO3-] approximately equal to 31), or severe alkalosis (pH approximately equal to 7.6, [HCO3-] approximately equal to 39) and measured JCa+ and the release of osteoclastic beta-glucuronidase and osteoblastic collagen synthesis. Compared with control, metabolic alkalosis caused a progressive decrease in JCa+, which was correlated inversely with initial medium pH (pHi). Alkalosis caused a decrease in osteoclastic beta-glucuronidase release, which was correlated inversely with pHi and directly with JCa+. Alkalosis also caused an increase in osteoblastic collagen synthesis, which was correlated directly with pHi and inversely with JCa+. There was a strong inverse correlation between the effects alkalosis on osteoclastic beta-glucuronidase release and osteoblastic collagen synthesis. Thus metabolic alkalosis decreases JCa+ from bone, at least in part, by decreasing osteoclastic resorption and increasing osteoblastic formation. These results suggest that the provision of base to neutralize endogenous acid production may improve bone mineral accretion.

Mechanism of proton-induced bone calcium release: calcium carbonate-dissolution

1987 ◽  
Vol 253 (5) ◽  
pp. F998-F1005 ◽  
Author(s):  
D. A. Bushinsky ◽  
R. J. Lechleider
Keyword(s):  
Metabolic Acidosis ◽  
Calcium Carbonate ◽  
Bone Mineral ◽  
Calcium Release ◽  
Calcium Efflux ◽  
Carbonate Phase ◽  
Bone Calcium ◽  
Calcium Carbonate Dissolution

Protons are buffered and calcium is released by bone during metabolic acidosis. Incubation of neonatal mouse calvariae in acid medium causes net calcium efflux from bone and net proton influx into bone, just as metabolic acidosis does in vivo. To determine whether the calcium carbonate phase of bone mineral is solubilized with increasing proton concentrations, we cultured calvariae for 3 h in medium in which the saturation was varied by changing pH or calcium and phosphate concentrations. We determined the driving force for crystallization by calculating the Gibbs free energy of formation (DG). With alteration of the medium pH, calcium carbonate entry or loss from bone varied linearly with the initial DG for medium calcium carbonate (r = -0.745, n = 41, P less than 0.001) as it did with alteration of the medium calcium and phosphate (r = -0.665, n = 118, P less than 0.001). There was dissolution of calcium carbonate into medium that was unsaturated with respect to calcium carbonate, net flux ceased at saturation, and calcium carbonate entered bone from supersaturated medium, indicating that the medium is in equilibrium with the calcium carbonate phase of bone mineral. Neither the mineral phase brushite nor apatite was in equilibrium with the medium. These observations indicate that in vitro, acute proton-induced calcium efflux is due to dissolution of bone calcium carbonate.

Glucose enhancement of transcellular calcium transport in the intestine

1988 ◽  
Vol 255 (3) ◽  
pp. G339-G345 ◽  
Author(s):  
K. M. Carroll ◽  
R. J. Wood ◽  
E. B. Chang ◽  
I. H. Rosenberg
Keyword(s):  
Calcium Transport ◽  
Calcium Uptake ◽  
Calcium Absorption ◽  
Membrane Integrity ◽  
Calcium Flux ◽  
Calcium Efflux ◽  
Cell Membrane Integrity ◽  
Active Calcium ◽  
Altered Cell

Glucose stimulates calcium transport in vitro in rat duodenal tissue and isolated enterocytes. Under short-circuited conditions, glucose increased mucosal to serosal calcium flux (JCa(m----s)) without altering serosal to mucosal calcium flux (JCa(s----m)) in the duodenum, the primary site of active calcium absorption in the rat small intestine. The half-maximal dose (ED50) of the glucose stimulatory effect was less than 1 mM, and an increase in JCa(m----s) of 80% over control was seen at a glucose concentration of 50 mM. Glucose did not increase calcium flux in the ileum where active calcium absorption is minimal. Glucose stimulated net calcium uptake by 35% in isolated duodenal enterocytes. Glucose did not alter calcium efflux from preloaded enterocytes suspended in calcium-free buffer. Glucose enhancement of net calcium uptake in enterocytes was not caused by altered cell membrane integrity or functional viability. The nonmetabolizable glucose analogue alpha-methylglucoside did not stimulate calcium transport. Our findings suggest that glucose can stimulate intestinal calcium absorption, at least partially, by enhancing transcellular calcium transport and that cellular glucose metabolism is necessary for stimulation of this route of calcium transport.

Maitotoxin stimulates hormonal release and calcium flux in rat anterior pituitary cells in vitro

1984 ◽  
Vol 247 (4) ◽  
pp. E520-E525
Author(s):  
G. Schettini ◽  
K. Koike ◽  
I. S. Login ◽  
A. M. Judd ◽  
M. J. Cronin ◽  
...  
Keyword(s):  
Calcium Channels ◽  
Anterior Pituitary ◽  
Calcium Influx ◽  
Calcium Flux ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Anterior Pituitary Cells ◽  
Lh Release ◽  
Hormonal Release

The marine dinoflagellate toxin maitotoxin (MTX), an activator of calcium channels, stimulates the release of prolactin (PRL), growth hormone (GH), thyroid-stimulating hormone (TSH), and luteinizing hormone (LH) from monolayers of anterior pituitary cells in a dose-dependent manner. Maitotoxin significantly increased PRL, GH, and LH release within 1.5 min and TSH release within 3.5 min, and the stimulation continued for at least 1 h (P less than 0.01). MTX-stimulated hormonal release was blocked by the calcium channel blocker manganese (P less than 0.01). In freshly dispersed perifused pituitary cells in columns, exposure to MTX for 10 min markedly increased PRL, GH, TSH, and LH release for at least 1 h after withdrawal of the toxin. In other experiments, MTX significantly stimulated 45Ca2+ exchange by dispersed pituitary cells within 30 s, continuing for at least 30 min. We conclude that MTX increases anterior pituitary hormonal release, possibly by activating calcium channels, thereby increasing cellular calcium influx. Thus MTX may be a useful agent for investigating the involvement of Ca2+ in hormonal secretory processes.

Greater unidirectional calcium efflux from bone during metabolic, compared with respiratory, acidosis

1992 ◽  
Vol 262 (3) ◽  
pp. F425-F431 ◽  
Author(s):  
D. A. Bushinsky ◽  
N. E. Sessler ◽  
N. S. Krieger
Keyword(s):  
Driving Force ◽  
Respiratory Acidosis ◽  
Mineral Dissolution ◽  
Calcium Flux ◽  
Calcium Efflux ◽  
Carbonated Apatite ◽  
Acid Base Status ◽  
45Ca Efflux ◽  
45Ca Release

There is a smaller net calcium efflux from bone in vitro during respiratory (increased PCO2) than metabolic (decreased [HCO3-] acidosis. This could be due to the elevated PCO2, which would lessen the driving force for mineral dissolution and increase the driving force for mineralization with respect to carbonated apatite in the bone mineral. To test this hypothesis, we injected neonatal mice with 45Ca and dissected the radiolabeled calvariae 24 h later. The live calvariae were then cultured for 24 h under conditions simulating respiratory acidosis (Resp, pH = 7.225 +/- 0.003, PCO2 = 87.5 +/- 0.1 mmHg), severe respiratory acidosis (SResp, pH = 7.072 +/- 0.004, PCO2 = 103.0 +/- 0.5 mmHg), metabolic acidosis (Met, pH = 7.212 +/- 0.003, HCO3- = 15.5 +/- 0.1 meq/l), or normal acid-base status (Ctl, pH = 7.452 +/- 0.003, PCO2 = 40.0 +/- 0.2 mmHg, HCO3- = 27.8 +/- 0.2 meq/l) and bidirectional net calcium flux (JCa) and unidirectional 45Ca release were determined. There was greater JCa from bone during Met than Resp, and JCa was not different from Met during SResp despite the latter having a significantly lower pH. There was greater unidirectional 45Ca release from bone during Met than Resp, SResp, or Ctl. There was a similar direct correlation between JCa and 45Ca efflux in the respiratory and metabolic groups. However, when calvarial osteoclast activity was inhibited with calcitonin,although there was again greater JCa and 45Ca release with a metabolic compared with respiratory acidosis, there was a greater proportion of 45Ca release than JCa from bone.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals What is the purpose of the large sarcolemmal calcium flux on each heartbeat?

2009 ◽  
Vol 297 (2) ◽  
pp. H493-H494 ◽  
Author(s):  
D. A. Eisner ◽  
A. W. Trafford
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Calcium Release ◽  
Calcium Influx ◽  
Calcium Content ◽  
Significant Fraction ◽  
Alternative Strategy ◽  
Calcium Flux ◽  
Rapid Changes ◽  
Inotropic Responses

In cardiac muscle, although most of the calcium that activates contraction comes from the sarcoplasmic reticulum (SR), a significant fraction (up to 30%, depending on the species) enters from outside the cell and is then pumped out at the end of systole. Although some of this calcium influx is required to trigger calcium release from the SR, the bulk serves to reload the cell (and thence the SR) with calcium to replace the calcium that is pumped out of the cell. An alternative strategy would be for the heart to have a much smaller calcium influx balancing a smaller efflux. We demonstrate that this would result in a slowing of inotropic responses due to changes of SR calcium content. We conclude that the large sarcolemmal calcium fluxes facilitate rapid changes of contractility.

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