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 Ca2+ overload was attenuated and transient in the presence of ruthenium red, CGP-37157 and cyclosporin A.


CONCLUSIONS
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.
Ban
K
K
Department of Medicine, School of Medicine, Tokai University, Kanagawa, Japan. ban@is.icc.u-tokai.ac.jp
Handa
S
S
Chapman
R A
RA
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002478:Cells, Cultured; D002998:Clonazepam / Q000031:analogs & derivatives / Q000494:pharmacology; D016572:Cyclosporine / Q000494:pharmacology; D003864:Depression, Chemical; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D007425:Intracellular Membranes / Q000187:drug effects* / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D008297:Male; D008856:Microscopy, Fluorescence; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D012430:Ruthenium Red / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors; D013841:Thiazepines / Q000494:pharmacology
D004791:Enzyme Inhibitors; D017923:Sodium-Hydrogen Exchangers; D013841:Thiazepines; D012430:Ruthenium Red; D002998:Clonazepam; C079032:CGP 37157; D016572:Cyclosporine; D000255:Adenosine Triphosphate; D012964:Sodium; D009247:NADH, NADPH Oxidoreductases; D008274:Magnesium; D002118:Calcium