Stojilković S S, Stutzin A, Izumi S, Dufour S, Torsello A, Virmani M A, Rojas E, Catt K J
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
New Biol. 1990 Mar;2(3):272-83.
Gonadotropin-releasing hormone (GnRH) stimulates characteristic biphasic increases in cytosolic calcium concentration ([Ca2+]i) and in luteinizing hormone (LH) release in cultured gonadotrophs, with an early peak followed by a prolonged plateau in both responses. Analysis of [Ca2+]i by dual-wavelength fluorimetric assay and of LH release at 5-sec intervals in perifused pituitary cells revealed increases in both responses within a few seconds of exposure to GnRH. The maximum elevation of [Ca2+]i occurred within 20 sec, and the peak gonadotropin release in 35 sec; the total duration of the spike phase for both [Ca2+]i and LH release was 2.5 min. Under extracellular Ca2(+)-deficient conditions, the GnRH-induced peak in [Ca2+]i was reduced by about 20% and the plateau phase was abolished. Concomitantly, the magnitude of the acute phase of LH release was reduced by 40% and that of the second phase by about 90%. Recovery of the plateau phase of LH release occurred within 25 sec after addition of 1.25 mM Ca2+ to Ca2(+)-deficient medium. In a dose-dependent manner, the non-selective Ca2+ channel blockers Co2+ and Cd2+ reduced the Ca2+ current measured by whole-cell recording in pituitary gonadotrophs and abolished the extracellular Ca2(+)-dependent component of LH release. The selective calcium channel blocker, nifedipine, decreased the magnitude of the Ca2+ current and reduced the plateau phase of LH release by 50%; conversely, the dihydropyridine agonist methyl, 1,4,dihydro-2,6-dimethyl 3-nitro-4-(2-trifluorome) (Bay K 8644) consistently enhanced the amplitudes of both Ca2+ current and GnRH-induced LH release. These data reveal a close temporal correlation between changes in [Ca2+]i and LH release during GnRH action, with Ca2+ mobilization during the spike phase and Ca2+ influx through dihydropyridine-sensitive and insensitive sets of receptor-operated calcium channels during the spike and plateau phases. In addition, analysis of the magnitudes of the [Ca2+]i and LH responses to a wide range of GnRH concentrations in the presence and absence of extracellular Ca2+ is consistent with amplification of the [Ca2+]i signal in agonist-stimulated gonadotrops.
促性腺激素释放激素（GnRH）刺激培养的促性腺细胞中胞质钙浓度（[Ca2+]i）和促黄体生成素（LH）释放出现典型的双相增加，两种反应均先有一个早期峰值，随后是一个延长的平台期。通过双波长荧光测定法分析[Ca2+]i，并在灌流垂体细胞中每隔5秒分析一次LH释放，结果显示在暴露于GnRH后的几秒钟内，两种反应均增加。[Ca2+]i的最大升高在20秒内出现，促性腺激素释放峰值在35秒内出现；[Ca2+]i和LH释放的尖峰期总持续时间为2.5分钟。在细胞外缺钙条件下，GnRH诱导的[Ca2+]i峰值降低约20%，平台期消失。与此同时，LH释放急性期的幅度降低40%，第二阶段降低约90%。在缺钙培养基中加入1.25 mM Ca2+后25秒内，LH释放的平台期恢复。非选择性钙通道阻滞剂Co2+和Cd2+以剂量依赖的方式降低了垂体促性腺细胞中通过全细胞记录测量的钙电流，并消除了LH释放的细胞外钙依赖性成分。选择性钙通道阻滞剂硝苯地平降低了钙电流的幅度，并使LH释放的平台期降低了50%；相反，二氢吡啶激动剂甲基-1,4-二氢-2,6-二甲基-3-硝基-4-(2-三氟甲基)（Bay K 8644）持续增强钙电流和GnRH诱导的LH释放的幅度。这些数据揭示了GnRH作用期间[Ca2+]i变化与LH释放之间密切的时间相关性，在尖峰期有钙动员，在尖峰期和平台期有钙通过二氢吡啶敏感和不敏感的受体操纵钙通道流入。此外，在有和没有细胞外Ca2+的情况下，分析[Ca2+]i和LH对广泛GnRH浓度的反应幅度，与激动剂刺激的促性腺细胞中[Ca2+]i信号的放大一致。
