Ojeda S R, Negro-Vilar A
Neuroendocrinology. 1984 Nov;39(5):442-7. doi: 10.1159/000124018.
The present experiments were performed to investigate the role of extracellular Ca2+ in the process of prostaglandin E2 (PGE2) release from the median eminence (ME) of the hypothalamus. Changes in the release of LHRH were also evaluated. Incubation of ME fragments with different concentrations of K+ induced a dose-related increase in PGE2 and LHRH release. The effect of K+ depended upon the Ca2+ concentration in the incubation medium. A Ca2+ concentration of 0.1 mM was sufficient to permit a significant response in both PGE2 and LHRH release to K+. The effect of a maximal K+ concentration (56 mM) was almost completely obliterated by omitting Ca2+ from the incubation medium and by chelating the remaining Ca2+ with EDTA or EGTA. The Ca2+ ionophore A23187, tested at different concentrations (1-50 microM) significantly increased the release of both PGE2 and LHRH from the ME in a Ca2+-dependent manner. A Ca2+ concentration of 0.25 mM allowed maximal LHRH response to the ionophore, but permitted only a partial (50%) PGE2 response. Blockade of Ca2+ channels with Verapamil, a Ca2+ entry blocker, prevented the effect of K+ on both PGE2 and LHRH release in a dose-dependent manner. The results demonstrate that release of PGE2 from ME nerve terminals depends upon the concentration of extracellular Ca2+ and suggest that PGE2 release is initiated by an increase in Ca2+ influx to the terminals. In addition, the data provide further evidence that release of LHRH is, to a significant extent, a function of Ca2+ influx through Ca2+ voltage-dependent channels.
进行本实验以研究细胞外钙离子在前列腺素E2（PGE2）从下丘脑正中隆起（ME）释放过程中的作用。同时也评估了促黄体生成素释放激素（LHRH）释放的变化。用不同浓度的钾离子孵育ME片段可导致PGE2和LHRH释放呈剂量相关增加。钾离子的作用取决于孵育培养基中的钙离子浓度。0.1 mM的钙离子浓度足以使PGE2和LHRH释放对钾离子产生显著反应。通过从孵育培养基中去除钙离子以及用乙二胺四乙酸（EDTA）或乙二醇双乙醚二胺四乙酸（EGTA）螯合剩余钙离子，最大钾离子浓度（56 mM）的作用几乎完全消除。以不同浓度（1 - 50 μM）测试的钙离子载体A23187以钙离子依赖的方式显著增加了ME中PGE2和LHRH的释放。0.25 mM的钙离子浓度使LHRH对离子载体产生最大反应，但仅允许PGE2产生部分（50%）反应。用钙离子通道阻滞剂维拉帕米阻断钙离子通道，以剂量依赖的方式阻止了钾离子对PGE2和LHRH释放的作用。结果表明，ME神经末梢PGE2的释放取决于细胞外钙离子浓度，并提示PGE2的释放是由钙离子流入末梢增加所启动的。此外，数据进一步证明，LHRH的释放很大程度上是钙离子通过电压依赖性钙离子通道流入的函数。
