Calcium- and ADP-magnesium-induced respiratory uncoupling in isolated cardiac mitochondria: Influence of cyclosporin A

This study was designed to determine the effect of calcium and ADP-Mg on th e oxidative phosphorylation in isolated cardiac mitochondria. The influence of cyclosporin A was also evaluated. The mitochondria were extracted from rat ventricles. Their oxidative phosphorylations were determined in two res piration media with different free Ca2+ concentrations. Respiration was det ermined with palmitoylcarnitine and either ADP(-) or ADP-Mg. With elevated free Ca2+ concentrations and ADP-Mg, the transition state III to state IV r espiration did not occurred. The ADP:O ratio was reduced. The phenomenon wa s not observed in the other experimental conditions (low free Ca2+ concentr ation with either ADP(-) or ADP-Mg or elevated free Ca2+ concentration with ADP(-)). Uncoupling was allied with a constant AMP production, which maint ained an elevated ADP level in the respiration medium and prevented the ret urn to state IV respiration. It was also observed in a respiration medium d evoid of free Ca2+ when the mitochondria were pre-loaded with Ca2+. Uncoupl ing was inhibited by cyclosporin A. Furthermore, the Krebs cycle intermedia tes released from C-14-palmitoylcarnitine oxidation revealed that succinate was increased by elevated free Ca2+ and ADP-Mg. Succinate is a FAD-linked substrate with low respiration efficiency. Its accumulation could account f or the decreased ADP:O ratio. The Ca2+- and ADP-Mg-induced uncoupling might be partly responsible for the mechanical abnormalities observed during low -flow ischemia.