Cano-Abad M F, Villarroya M, García A G, Gabilan N H, López M G
Instituto de Farmacologia Teófilo Hernando, Departamento de Farmacologia, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo 4, Madrid 28029, Spain.
J Biol Chem. 2001 Oct 26;276(43):39695-704. doi: 10.1074/jbc.M102334200. Epub 2001 Aug 10.
Sustained, mild K+ depolarization caused bovine chromaffin cell death through a Ca(2+)-dependent mechanism. During depolarization, Ca(2+) entered preferentially through L-channels to induce necrotic or apoptotic cell death, depending on the duration of the cytosolic Ca(2+) concentration (Ca(2+)) signal, as proven by the following. (i) The L-type Ca(2+) channel activators Bay K 8644 and FPL64176, more than doubled the cytotoxic effects of 30 mm K+; (ii) the L-type Ca(2+) channel blocker nimodipine suppressed the cytotoxic effects of K+ alone or K+ plus FPL64176; (iii) the potentiation by FPL64176 of the K+ -evoked Ca(2+) elevation was totally suppressed by nimodipine. Cell exposure to K+ plus the L-type calcium channel agonist FPL64176 caused an initial peak rise followed by a sustained elevation of the Ca(2+) that, in turn, increased Ca(2+) and caused mitochondrial membrane depolarization. Cyclosporin A, a blocker of the mitochondrial transition pore, and superoxide dismutase prevented the apoptotic cell death induced by Ca(2+) overload through L-channels. These results suggest that Ca(2+) entry through L-channels causes both calcium overload and mitochondrial disruption that will lead to the release of mediators responsible for the activation of the apoptotic cascade and cell death. This predominant role of L-type Ca(2+) channels is not shared by other subtypes of high threshold voltage-dependent neuronal Ca(2+) channels (i.e. N, P/Q) expressed by bovine chromaffin cells.
持续的轻度钾离子去极化通过一种依赖钙离子的机制导致牛嗜铬细胞死亡。在去极化过程中，钙离子优先通过L型通道进入细胞，根据胞质钙离子浓度（[Ca(2+)]c）信号的持续时间诱导坏死或凋亡性细胞死亡，如下所示。（i）L型钙离子通道激活剂Bay K 8644和FPL64176使30 mM钾离子的细胞毒性作用增加了一倍多；（ii）L型钙离子通道阻滞剂尼莫地平抑制了单独钾离子或钾离子加FPL64176的细胞毒性作用；（iii）尼莫地平完全抑制了FPL64176对钾离子诱发的[Ca(2+)]c升高的增强作用。细胞暴露于钾离子加L型钙通道激动剂FPL64176会导致[Ca(2+)]c先出现峰值升高，随后持续升高，进而增加[Ca(2+)]m并导致线粒体膜去极化。线粒体通透性转换孔的阻滞剂环孢素A和超氧化物歧化酶可防止由L型通道引起的钙离子过载诱导的凋亡性细胞死亡。这些结果表明，通过L型通道进入的钙离子会导致钙离子过载和线粒体破坏，进而导致负责激活凋亡级联反应和细胞死亡的介质释放。牛嗜铬细胞表达的其他高阈值电压依赖性神经元钙离子通道亚型（即N型、P/Q型）并不具有L型钙离子通道的这种主要作用。
