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 the 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 respiration media with different free Ca2+ concentrations. Respiration was determined with palmitoylcarnitine and either ADP or ADP-Mg. With elevated free Ca2+ concentrations and ADP-Mg, the transition state III to state IV respiration did not occurred. The ADP:O ratio was reduced. The phenomenon was not observed in the other experimental conditions (low free Ca2+ concentration with either ADP- or ADP-Mg or elevated free Ca2+ concentration with ADP-). Uncoupling was allied with a constant AMP production, which maintained an elevated ADP level in the respiration medium and prevented the return to state IV respiration. It was also observed in a respiration medium devoid of free Ca2+ when the mitochondria were pre-loaded with Ca2+. Uncoupling was inhibited by cyclosporin A. Furthermore, the Krebs cycle intermediates released from 14C-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 for 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.
Sentex
E
E
INRA, Unité de Nutrition Lipidique, BV 1540, Dijon, France.
Laurent
A
A
Martine
L
L
Gregoire
S
S
Rochette
L
L
Demaison
L
L
D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002952:Citric Acid Cycle / Q000187:drug effects; D016572:Cyclosporine / Q000494:pharmacology*; D006352:Heart Ventricles; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D008297:Male; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism*; D010085:Oxidative Phosphorylation / Q000187:drug effects*; D010101:Oxygen Consumption / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D014475:Uncoupling Agents / Q000494:pharmacology*
D014475:Uncoupling Agents; D000244:Adenosine Diphosphate; D016572:Cyclosporine; D008274:Magnesium; D002118:Calcium