Intracellular free Ca2+, Na+, and H+ concentrations in the isolated perfused rat heart during the Ca2+ paradox.
Enzyme release from the normothermic perfused rat heart was determined to evaluate myocardial cell damage during the perfusion sequence of the Ca2+ Ca2+ paradox. In addition sarcosolic free Ca2+ and monovalent cation concentrations were measured using ion-selective microelectrodes (ISMEs). A reduction of the extracellular Ca2+ concentration, [Ca2+]e, from 1.0 mmol/l to 0.3 or 0.1 mmol/l, respectively, during the re-perfusion period markedly decreased the rate of enzyme release. Slow Ca2+ channel blockers were less (verapamil) or not at all (nifedipine) effective in providing protection. The sarcosolic free Ca2+ and Na+ concentrations, [Ca2+]i and [Na+]i, were significantly (P < 0.01) elevated during Ca(2+)-free perfusion, [H+]i was not significantly changed, while the membrane potential became continuously more positive. Addition of verapamil to the perfusion medium increased [Na+]i, but did not further increase [Ca2+]i. The critical [Ca2+]i for cell damage was between 12 and 18 mumol/l. It could be demonstrated, that Ca2+ entry during re-perfusion via Na/Ca exchange is thermodynamically unlikely to elevate [Ca2+]i to critical values. It is concluded therefore that the predisposition of the rat heart for the Ca2+ paradox is brought about by membrane leaks, which form during Ca(2+)-free perfusion and that Ca2+ influx into the sarcosol proceeds mainly through these leaks.
Diederichs
F
F
Institute of Clinical Biochemistry, Hannover Medical School, Germany.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003402:Creatine Kinase / Q000378:metabolism; D006321:Heart / Q000187:drug effects; D006859:Hydrogen / Q000378:metabolism; D066298:In Vitro Techniques; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008839:Microelectrodes; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D010477:Perfusion; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
D006859:Hydrogen; D012964:Sodium; D014700:Verapamil; D007770:L-Lactate Dehydrogenase; D003402:Creatine Kinase; D002118:Calcium