The voltage-independent B-type Ca2+ channel modulates apoptosis of cardiac myocytes

In cardiac myocytes, Ca2+ is the second messenger of various physiological processes, including the excitation-contraction coupling phenomenon. Here, we examined how Ca2+ regulates cardiac myocyte apoptosis. Using an adult rat ventricular myocyte culture model, we found that ceramide (Cer) induces an apoptotic process that is highly sensitive to calcium: it is inhibited by the Ca2+buffer BAPTA-AM and is potentiated by the Ca2+ ionophore ionomycin. Cer-treated myocytes maintained their Ca2+ homeostasis and normal activity of their voltage-dependent sarcolemmal Ca2+ entry pathways but showed enhanced activity of B-type Ca2+ channels that were stimulated by Cer in the inside-out patch clamp configuration. Pharmacological modulations of B-type Ca2+ channels modulated Cer-induced apoptosis. Mitochondria were involved in Cer-induced apoptosis, as indicated by the inhibitory effect of cyclosporine A and caspase-9 inhibitor. Both the loss of mitochondrial membrane potential and the caspase-9 activation in Cer-treated myocytes were attenuated by blocking B-type Ca2+ channels. The mitochondrial Ca2+ content was evaluated as changes in [Ca2+]i after a short application of a mitochondrial uncoupler, FCCP, was increased in Cer-treated cells. Together, these results show that Ca2+ modulates Cer-induced cardiac myocyte apoptosis through the coupling of B-type Ca2+ channels with mitochondria.