Chang J P, McCoy E E, Graeter J, Tasaka K, Catt K J
J Biol Chem. 1986 Jul 15;261(20):9105-8.
The roles of calcium ions and voltage-sensitive calcium channels in gonadotropin-releasing hormone (GnRH)-stimulated luteinizing hormone (LH) release were investigated in rat anterior pituitary cells. The calcium ionophores A23187 and ionomycin stimulated LH release from cultured pituitary cells, in which ionomycin (5 X 10(-5) M) was as effective as a maximal concentration of GnRH (10(-8) M). In addition, a concentration of the calcium channel agonist methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine- 5-carboxylate (BK 8644) (10(-8) M), which did not alter basal LH release, potentiated the ability of submaximal (10(-10) and 10(-9) M) doses of GnRH to increase LH secretion. Furthermore, concentrations of the calcium channel antagonist nitrendipine (10(-8)-10(-5) M) that did not alter basal LH release, inhibited GnRH-stimulated LH secretion by 30-40%. Nitrendipine (10(-8) M) also blocked the potentiation of GnRH-induced LH secretion by BK 8644. During column perifusion of pituitary cells, 10(-8) M nitrendipine reduced the LH response to a 2-min pulse of 10(-8) M GnRH by about 40%. In Quin-2-loaded pituitary cells, supramaximal doses (10(-6) M) of a potent GnRH agonist rapidly elevated cytoplasmic Ca2+ by 50-100 nM. Concomitant treatment with nitrendipine decreased the GnRH agonist-induced Ca2+ signal by 40-60%. These results indicate that increases in intracellular Ca2+ via voltage-sensitive calcium channels partially reproduce GnRH action, and also that GnRH causes activation of such channels. However, the increase in cytoplasmic Ca2+ concentration during GnRH action must originate in part from mobilization of internal Ca2+ stores, and its relatively small magnitude may be consistent with the concomitant activation of protein kinase C as an intermediate step in GnRH action.
在大鼠垂体前叶细胞中研究了钙离子和电压敏感性钙通道在促性腺激素释放激素（GnRH）刺激促黄体生成素（LH）释放中的作用。钙离子载体A23187和离子霉素刺激培养的垂体细胞释放LH，其中离子霉素（5×10⁻⁵M）的效果与最大浓度的GnRH（10⁻⁸M）相同。此外，钙通道激动剂1,4-二氢-2,6-二甲基-3-硝基-4-（2-三氟甲基苯基）-吡啶-5-羧酸甲酯（BK 8644）（10⁻⁸M）的浓度不改变基础LH释放，但能增强次最大剂量（10⁻¹⁰和10⁻⁹M）的GnRH增加LH分泌的能力。此外，钙通道拮抗剂尼群地平（10⁻⁸ - 10⁻⁵M）的浓度不改变基础LH释放，但能抑制GnRH刺激的LH分泌30 - 40%。尼群地平（10⁻⁸M）也能阻断BK 8644对GnRH诱导的LH分泌的增强作用。在垂体细胞的柱式灌流过程中，10⁻⁸M尼群地平使LH对10⁻⁸M GnRH的2分钟脉冲的反应降低约40%。在负载喹啉-2的垂体细胞中，超最大剂量（10⁻⁶M）的强效GnRH激动剂使细胞质Ca²⁺迅速升高50 - 100 nM。同时用尼群地平处理可使GnRH激动剂诱导的Ca²⁺信号降低40 - 60%。这些结果表明，通过电压敏感性钙通道增加细胞内Ca²⁺可部分重现GnRH的作用，并且GnRH可导致此类通道的激活。然而，GnRH作用期间细胞质Ca²⁺浓度的增加必定部分源于细胞内钙库的动员，其相对较小的幅度可能与作为GnRH作用中间步骤的蛋白激酶C的伴随激活相一致。
