On the mechanism of the failure of mitochondrial function in isolated guinea-pig myocytes subjected to a Ca2+ overload

Objective: The influence of agents that inhibit the movement of Ca2+ across the mitochondrial membrane or Ca2+ dependent changes to this membrane upon the response of isolated ventricular myocytes to a Ca2+ overload has been investigated. Methods: The changes of intracellular Ca2+ and Mg2+ ([Ca2+](i), [Mg2+](i)) (as reflected by cellular ATP), mitochondrial membrane potential (Psi(m)) and NADH was measured upon the response of isolated ventricular myocytes to a Ca2+ overload. Results: A slow depolarization of Psi(m) during Ca2+ depletion and its prompt recovery on Ca2+ repletion were unaffected by ruthenium red, clonazepam, CGP-37157 which is a high potent inhibitor of the mitochondrial Na+/Ca2+ antiport or cyclosporin A but a large delayed sustained depolarization was inhibited. The slow small fall in [Mg2+](i) on Ca2+ depletion and a rapid recovery on Ca2+ repletion were unaffected by ruthenium red, clonazepam, CGP-37157 or cyclosporin A. A delayed sustained larger rise in [Mg2+](i) was inhibited. The marked sustained fall in NADH autofluorescence that occurs on Gait overload was attenuated and transient in the presence of ruthenium red, CGP-37157 and cyclosporin A. Conclusion: These results are consistent with an increase in Ca2+ cycling across the mitochondrial membrane provoked by the combined Na+ and Ca2+ overload of cardiac myocytes, causing a depolarization sufficient to uncouple respiration and lead to the depletion of cellular ATP. (C) 1999 Elsevier Science B.V. All rights reserved.