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

Sustained, mild K+ depolarization caused bovine chromaffin cell death throu gh a Ca2+-dependent mechanism. During depolarization, Ca2+ entered preferen tially through L-channels to induce necrotic or apoptotic cell death, depen ding 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 effec ts of K+ alone or K+ plus FPL64176; (iii) the potentiation by FPL64176 of t he 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 depolarizati on. Cyclosporin A, a blocker of the mitochondrial transition pore, and supe roxide dismutase prevented the apoptotic cell death induced by Ca2+ overloa d through L-channels. These results suggest that Ca2+ entry through L-chann els causes both calcium overload and mitochondrial disruption that will lea d to the release of mediators responsible for the activation of the apoptot ic 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.