Schwiening C J, Kennedy H J, Thomas R C
Department of Physiology, The School of Medical Sciences, University Walk, Bristol BS8 1TD, UK.
Proc Biol Sci. 1993 Sep 22;253(1338):285-9. doi: 10.1098/rspb.1993.0115.
The submicromolar levels of free Ca(2+) ions in animal cells are believed to be maintained in the long term by two different plasma membrane transport mechanisms. These are Na-Ca exchange, driven by the sodium gradient, and a Na-independent Ca pump, driven by ATP. There is good evidence from red blood cells, and indirect evidence from other non-neuronal preparations, that the Ca-ATPase exchanges internal Ca(2+) for external H(+). Although Ca extrusion from nerve cells is inhibited by high external pH, there as yet is no evidence for the counter-transport of H(+). We have used both pH- and calcium-sensitive microelectrodes on the cell surface, and the Ca indicator fura-2 intracellularily, to investigate how snail neurons regulate cytoplasmic free Ca(2+). We now report that in snail neurons the recovery of intracellular Ca(2+) after an increase coincides with both the expected increase in surface Ca(2+) and a decrease in surface H+. Recovery of intracellular Ca and the changes in surface pH and Ca are all blocked by intracellular vanadate. We conclude that snail neurons regulate intracellular Ca mainly by a Ca-H ATPase, and suggest that this Ca-H exchange may account for many of the reported extracellular pH changes seen with neuronal excitation.
动物细胞中游离钙离子的亚微摩尔水平被认为长期通过两种不同的质膜转运机制维持。这两种机制分别是由钠梯度驱动的钠钙交换，以及由ATP驱动的不依赖钠的钙泵。红细胞有充分证据，其他非神经元制剂也有间接证据表明，钙ATP酶将细胞内的钙离子与细胞外的氢离子进行交换。尽管高细胞外pH值会抑制神经细胞的钙排出，但尚无证据表明存在氢离子的反向转运。我们在细胞表面使用了对pH值和钙离子敏感的微电极，并在细胞内使用了钙离子指示剂fura-2，以研究蜗牛神经元如何调节细胞质中的游离钙离子。我们现在报告，蜗牛神经元中钙离子增加后细胞内钙离子的恢复与表面钙离子预期的增加以及表面氢离子的减少同时发生。细胞内钒酸盐会阻断细胞内钙离子的恢复以及表面pH值和钙离子的变化。我们得出结论，蜗牛神经元主要通过钙氢ATP酶调节细胞内钙离子，并表明这种钙氢交换可能解释了许多报道中神经元兴奋时细胞外pH值的变化。
