Vanecek J, Klein D C
Institute of Physiology, Czechoslovak Academy of Sciences, Prague.
Endocrinology. 1992 Aug;131(2):939-46. doi: 10.1210/endo.131.2.1322288.
Melatonin inhibits GnRH-stimulated release of LH from neonatal rat pituitary cells, probably by inhibiting GnRH-induced elevation of intracellular Ca2+. This effect of melatonin seems to involve inhibition of Ca2+ influx through voltage-sensitive channels. Accordingly, it is possible that melatonin could act by hyperpolarizing pituitary cells, which would close these channels. This issue was addressed here by determining if melatonin influences membrane potential. Membrane potential and intracellular Ca2+ were studied in neonatal rat pituitary cells in suspension, using bis-oxonol and Fluo-3 as fluorescent indicators, respectively. It was found that treatment with melatonin alone causes membrane hyperpolarization and that it has a repolarizing effect after GnRH-induced membrane depolarization. This effect on membrane potential appears to be mediated by high affinity melatonin receptors and a pertussis toxin-sensitive Na(+)-dependent mechanism; it is not dependent upon Ca2+, Cl-, or bicarbonate. This may be the molecular basis of action of melatonin in other tissues with high affinity melatonin receptors.
褪黑素抑制新生大鼠垂体细胞中促性腺激素释放激素（GnRH）刺激的促黄体生成素（LH）释放，这可能是通过抑制GnRH诱导的细胞内钙离子浓度升高来实现的。褪黑素的这种作用似乎涉及抑制通过电压敏感通道的钙离子内流。因此，褪黑素可能通过使垂体细胞超极化来发挥作用，而这会关闭这些通道。本文通过确定褪黑素是否影响膜电位来探讨这一问题。分别使用双苯甲酰羟肟酸和Fluo-3作为荧光指示剂，对悬浮的新生大鼠垂体细胞的膜电位和细胞内钙离子进行了研究。结果发现，单独使用褪黑素处理会导致膜超极化，并且在GnRH诱导的膜去极化后具有复极化作用。这种对膜电位的影响似乎是由高亲和力的褪黑素受体和百日咳毒素敏感的钠依赖性机制介导的；它不依赖于钙离子、氯离子或碳酸氢根。这可能是褪黑素在其他具有高亲和力褪黑素受体的组织中发挥作用的分子基础。
