McArdle C A, Poch A
Institute for Hormone and Fertility Research, Hamburg, Germany.
Endocrinology. 1992 Jun;130(6):3567-74. doi: 10.1210/endo.130.6.1534542.
Sustained GnRH-stimulated LH release requires extracellular Ca2+, but GnRH transiently increases LH release in Ca(2+)-free medium. Here we have tested the dependence of the transient effect on intracellular Ca2+ pools. In superfused pituitary cells three Ca(2+)-mobilizing stimuli (GnRH, A23187, and endothelin-1) all caused sustained increases in LH release in normal medium (plateau responses), but only transient increases in Ca(2+)-free medium (spike responses). In Ca(2+)-free medium, GnRH (10(-10) or 10(-9) M) increased LH release transiently and desensitized the cells to the LH-releasing effect of subsequent stimulation with 10(-7) M GnRH. This desensitization was reversed by brief exposure to Ca(2+)-containing medium between the two GnRH stimulation periods. Heterologous desensitization between GnRH and A23187 and between GnRH and endothelin-1 also occurred in Ca(2+)-free medium. Thapsigargin, which inhibits the endoplasmic reticulum Ca(2+)-ATPase and thereby elevates cytosolic Ca2+, stimulated LH release (EC50, approximately 20 microM) in static culture, an effect which, unlike those of GnRH and A23187, was not markedly reduced in Ca(2+)-free medium. Low doses of thapsigargin, which had no effect on LH release alone, inhibited both sustained GnRH-stimulated LH release from static cultures in normal medium and transient GnRH-stimulated LH release from cells superfused in Ca(2+)-free medium. These data suggest that the spike phase of GnRH-stimulated LH release is not only associated with but is also dependent upon the mobilization of a GnRH- and thapsigargin-sensitive intracellular Ca2+ pool and that the Ca2+ pool mediating this GnRH effect is identical to or substantially interchangeable with A23187- and endothelin-1-mobilizable intracellular Ca2+ pools. Inhibition of sustained GnRH-stimulated LH release by thapsigargin also suggests the involvement of an intracellular Ca2+ pool in this phase of GnRH action.
持续的促性腺激素释放激素（GnRH）刺激的促黄体生成素（LH）释放需要细胞外钙离子（Ca2+），但GnRH在无钙培养基中可短暂增加LH释放。在此，我们测试了这种短暂效应对细胞内Ca2+库的依赖性。在灌流的垂体细胞中，三种可动员Ca2+的刺激物（GnRH、A23187和内皮素-1）在正常培养基中均引起LH释放持续增加（平台反应），但在无钙培养基中仅引起短暂增加（尖峰反应）。在无钙培养基中，GnRH（10^-10或10^-9 M）短暂增加LH释放，并使细胞对随后用10^-7 M GnRH刺激的LH释放效应脱敏。在两个GnRH刺激期之间短暂暴露于含钙培养基可逆转这种脱敏。在无钙培养基中，GnRH与A23187之间以及GnRH与内皮素-1之间也发生异源脱敏。毒胡萝卜素可抑制内质网Ca2+ -ATP酶，从而升高胞质Ca2+，在静态培养中刺激LH释放（半数有效浓度[EC50]约为20 microM），与GnRH和A23187不同，这种效应在无钙培养基中并未明显降低。低剂量的毒胡萝卜素单独对LH释放无影响，但可抑制正常培养基中静态培养物中持续的GnRH刺激的LH释放以及无钙培养基中灌流细胞中短暂的GnRH刺激的LH释放。这些数据表明，GnRH刺激的LH释放的尖峰期不仅与GnRH和毒胡萝卜素敏感的细胞内Ca2+库的动员有关，而且还依赖于此，并且介导这种GnRH效应的Ca2+库与A23187和内皮素-1可动员的细胞内Ca2+库相同或基本可互换。毒胡萝卜素对持续的GnRH刺激的LH释放的抑制也表明细胞内Ca2+库参与了GnRH作用的这一阶段。
