Endothelin-1 is a potent survival factor against myocardial cell apoptosis. While apoptotic stimuli often perturb mitochondrial function by decreasing the membrane potential as well as oxygen consumption, it is unknown whether ET-1 can rescue such perturbation by apoptotic stimuli. Administration of endothelin-1 inhibited the H(2)O(2)-induced release of cytochrome c from mitochondria to the cytosol in cardiac myocytes, indicating the involvement of the mitochondria-dependent pathway in the anti-apoptotic effect of endothelin-1. We showed here by cytofluorimetric analysis that endothelin-1 prevented the H(2)O(2)-induced decrease of membrane potential. However, endothelin-1 was unable to reverse the H(2)O(2)-mediated decrease in oxygen consumption and electron transport in the mitochondria of cardiac myocytes. Endothelin-1 was unable to rescue cardiac myocytes from apoptosis when administered after the decrease in mitochondrial membrane potential. These data suggest that endothelin-1 does not target the mitochondrial respiratory chain, but rather stabilizes the mitochondrial membrane during the protection against apoptosis.