Vergara L A, Stojilkovic S S, Rojas E
Laboratory of Cell Biology and Genetics, NIDDK, National Institutes of Health Bethesda, Maryland 20892, USA.
Biophys J. 1995 Oct;69(4):1606-14. doi: 10.1016/S0006-3495(95)80033-0.
Cultured rat pituitary gonadotrophs under whole-cell voltage clamp conditions respond to the hypothalamic hormone GnRH with synchronized oscillatory changes in both cytosolic Ca2+ concentration ([Ca2+]i) and [Ca2+]i-activated, apamin-sensitive K+ current (IK(Ca)). We found, and report here for the first time, that in GnRH-stimulated cells a brief depolarizing pulse can elicit a transient [Ca2+]i rise similar to the endogenous cycle. Furthermore, Ca2+ entry during a single depolarizing pulse was found to shift the phase of subsequent endogenous [Ca2+]i oscillations, which thereafter continue to occur at their previous frequency before the pulse. Application of two consecutive depolarizing pulses showed that the size of the [Ca2+]i rise evoked by the second pulse depended on the time lapsed between two consecutive pulses, indicating that each endogenous or evoked [Ca2+]i rise cycle leaves the Ca2+ release mechanism of the gonadotroph in a refractory state. Recovery from this condition can be described by an exponential function of the time lapsed between the pulses (time constant of ca. 1 s). We propose that the underlying mechanism in both refractoriness after endogenous cycles and phase resetting by a brief pulse of Ca2+ entry involves the InsP3 receptor-channel molecule presumed to be located on the cytosolic aspect of the endoplasmic reticulum membrane.
在全细胞膜片钳条件下培养的大鼠垂体促性腺激素细胞，对下丘脑激素促性腺激素释放激素（GnRH）产生反应，细胞溶质Ca2+浓度（[Ca2+]i）和[Ca2+]i激活的、蜂毒明肽敏感的K+电流（IK(Ca)）都会发生同步振荡变化。我们首次发现并在此报告，在GnRH刺激的细胞中，一个短暂的去极化脉冲可引发类似于内源性周期的[Ca2+]i短暂升高。此外，在单个去极化脉冲期间的Ca2+内流被发现会改变随后内源性[Ca2+]i振荡的相位，此后振荡会在脉冲之前的频率继续发生。施加两个连续的去极化脉冲表明，第二个脉冲引发的[Ca2+]i升高幅度取决于两个连续脉冲之间的时间间隔，这表明每个内源性或诱发的[Ca2+]i升高周期都会使促性腺激素细胞的Ca2+释放机制处于不应期。从这种状态恢复可以用脉冲之间的时间间隔的指数函数来描述（时间常数约为1秒）。我们提出，内源性周期后的不应期和短暂的Ca2+内流脉冲引起的相位重置的潜在机制都涉及假定位于内质网膜胞质侧的肌醇三磷酸受体通道分子。
