Calcium entry through L-type calcium channels causes mitochondrial disruption and chromaffin cell death

Sustained, mild K+ depolarization caused bovine chromaffin cell death through a Ca2+-dependent mechanism. During depolarization, Ca2+ entered preferentially through L-channels to induce necrotic or apoptotic cell death, depending on the duration of the cytosolic Ca2+ concentration ([Ca2+](c)) signal, as proven by the following. (i) The L-type Ca2+ channel activators Bay K 8644 and FPL64176, more than doubled the cytotoxic effects of 30 mm K+; (ii) the L-type Ca2+ channel blocker nimodipine suppressed the cytotoxic effects of K+ alone or K+ plus FPL64176; (iii) the potentiation by FPL64176 of the K+-evoked [Ca2+](c) 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 [Ca2+](c) that, in turn, increased [Ca2+](m) and caused mitochondrial membrane depolarization. Cyclosporin A, a blocker of the mitochondrial transition pore, and superoxide dismutase prevented the apoptotic cell death induced by Ca2+ overload through L-channels. These results suggest that Ca2+ 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 Ca2+ channels is not shared by other subtypes of high threshold voltage-dependent neuronal Ca2+ channels (i.e. N, P/Q) expressed by bovine chromaffin cells.