Polliotti B, Lebrun P, Robyn C, Meuris S
Research Laboratory on Reproduction, Faculty of Medicine (CP626), Free University of Brussels (ULB), Belgium.
Placenta. 1994 Jul;15(5):477-85. doi: 10.1016/s0143-4004(05)80417-5.
Isosmotical replacement of extracellular Na+ ([Na+]o) by K+, choline and to a lesser extent by saccharose stimulated the release of chorionic gonadotrophin and placental lactogen from human term placental explants. The effect of [Na+]o removal on the release of both hormones was concentration-dependent and was inhibited in the absence of extracellular Ca2+ or in the presence of 0.5 mM Co2+, a Ca2+ entry blocker. Blockers of the voltage-sensitive Ca2+ channels (20 microM nifedipine and 50 microM methoxyverapamil) or Na+ channels (5 microM tetrodotoxin) did not affect the stimulatory effects of [Na+]o omission. By contrast, Mg2+ and Sr2+ (10 mM) as well as amiloride (2 mM) and its analogue 2',4'-dimethylbenzamil (50 microns), all known to affect the Na(+)-Ca2+ exchange, markedly reduced the increase in hormone release elicited by [Na+]o removal. Lastly, the secretory responses to [Na+]o deprivation were increased in the presence of 2 mM ouabain, an inhibitor of the Na(+)-K+ ATPase. These results indicate for the first time that [Na+]o omission provokes a Ca(2+)-dependent stimulation of human chorionic gonadotrophin and placental lactogen releases. The pharmacological dissection of the secretory effects of [Na+]o removal supports the existence of a process of Na(+)-Ca2+ exchange in placental cells.
用K⁺、胆碱等渗替代细胞外Na⁺（[Na⁺]o），蔗糖在较小程度上替代，可刺激足月人胎盘外植体释放绒毛膜促性腺激素和胎盘催乳素。去除[Na⁺]o对两种激素释放的影响呈浓度依赖性，且在无细胞外Ca²⁺或存在0.5 mM Co²⁺（一种Ca²⁺进入阻滞剂）时受到抑制。电压敏感性Ca²⁺通道阻滞剂（20 μM硝苯地平、50 μM甲氧维拉帕米）或Na⁺通道阻滞剂（5 μM河豚毒素）不影响去除[Na⁺]o的刺激作用。相反，Mg²⁺和Sr²⁺（10 mM）以及氨氯地平（2 mM）及其类似物2',4'-二甲基苯甲酰胺（50 μM），这些都已知会影响Na⁺-Ca²⁺交换，显著降低了去除[Na⁺]o引起的激素释放增加。最后，在存在2 mM哇巴因（一种Na⁺-K⁺ ATP酶抑制剂）时，对[Na⁺]o剥夺的分泌反应增强。这些结果首次表明，去除[Na⁺]o会引发对人绒毛膜促性腺激素和胎盘催乳素释放的Ca²⁺依赖性刺激。对去除[Na⁺]o分泌效应的药理学剖析支持胎盘细胞中存在Na⁺-Ca²⁺交换过程。
