Bushinsky D A, Lechleider R J
Nephrology Program, Pritzker School of Medicine, University of Chicago, Illinois 60637.
Am J Physiol. 1987 Nov;253(5 Pt 2):F998-1005. doi: 10.1152/ajprenal.1987.253.5.F998.
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.
在代谢性酸中毒期间，质子被缓冲，钙由骨骼释放。将新生小鼠颅骨在酸性培养基中孵育会导致钙从骨骼净流出以及质子净流入骨骼，就如同代谢性酸中毒在体内发生的情况一样。为了确定骨矿物质的碳酸钙相是否会随着质子浓度的增加而溶解，我们在通过改变pH值、钙和磷酸盐浓度来改变饱和度的培养基中培养颅骨3小时。我们通过计算形成吉布斯自由能（DG）来确定结晶的驱动力。随着培养基pH值的改变，碳酸钙进入或从骨骼中流失与培养基碳酸钙的初始DG呈线性变化（r = -0.745，n = 41，P < 0.001），与培养基钙和磷酸盐的改变情况相同（r = -0.665，n = 118，P < 0.001）。碳酸钙会溶解到相对于碳酸钙不饱和的培养基中，在饱和度时净通量停止，并且碳酸钙会从过饱和培养基进入骨骼，这表明培养基与骨矿物质的碳酸钙相处于平衡状态。矿物相透钙磷石和磷灰石均与培养基不平衡。这些观察结果表明，在体外，急性质子诱导的钙流出是由于骨碳酸钙的溶解。
