Kojima I, Ogata E
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
Biochem Biophys Res Commun. 1989 Feb 15;158(3):1005-12. doi: 10.1016/0006-291x(89)92822-2.
When aequorin-loaded glomerulosa cells were incubated in isotonic Na2+-free medium containing N-methyl-D-glucamine instead of NaCl, there was an increase in cytoplasmic free calcium concentration, [Ca2+] c, which was not observed when extracellular calcium concentration was reduced to 1 microM. Upon removal of extracellular sodium, there was nearly five-fold increase in fractional efflux ratio of calcium. The reduction of extracellular sodium resulted in a stimulation of calcium influx rate, the magnitude of which was dependent on extracellular sodium concentration. Similar stimulation of calcium influx was observed when extracellular sodium was replaced with lithium. Nitrendipine did not affect the calcium influx induced by the reduction of extracellular sodium while a derivative of amiloride 3',4'-dichlorobenzamil, which inhibits Na-Ca exchange, attenuated calcium influx observed in sodium-free medium. These results indicate that removal of extracellular sodium leads to an increase in [Ca2+] c by stimulating calcium influx and that calcium enters the cell via Na-Ca exchanger.
当将装载水母发光蛋白的球状带细胞置于含有N - 甲基 - D - 葡糖胺而非氯化钠的等渗无钠培养基中培养时，细胞质游离钙浓度[Ca2+]c会升高，而当细胞外钙浓度降至1微摩尔时，并未观察到这种情况。去除细胞外钠后，钙的分数流出率增加了近五倍。细胞外钠的减少导致钙流入速率增加，其幅度取决于细胞外钠浓度。当用锂替代细胞外钠时，观察到类似的钙流入刺激。尼群地平不影响因细胞外钠减少而诱导的钙流入，而一种抑制钠 - 钙交换的阿米洛利衍生物3',4'-二氯苯甲酰胺可减弱在无钠培养基中观察到的钙流入。这些结果表明，去除细胞外钠通过刺激钙流入导致[Ca2+]c升高，并且钙通过钠 - 钙交换体进入细胞。
