Protection of isolated rat heart against the Ca2+ paradox. Are gap junction channels involved?
Enzyme release from isolated Langendorff-perfused rat hearts was studied under various protective conditions against the Ca2+ paradox. In addition sarcosolic free cation concentrations and the membrane potential were measured employing ion-selective microelectrode techniques during Ca(2+)-free perfusion. Low temperature (18 degrees C), low pH (6.5 or 6.1), and polyethylene glycol (9%) during Ca(2+)-free perfusion all protected isolated hearts against the Ca2+ paradox. Protection could only be afforded if the protective agent was continuously present from the beginning of the Ca(2+)-free perfusion period. A 10 min "normal" Ca(2+)-free pre-perfusion was sufficient to abolish the protective potency of the subsequent perfusion phase in the presence of the protective agent. The gap junction channel blocker heptanol (2 mmol/l) markedly decreased enzyme release during re-perfusion, but did not afford protection. Sarcosolic free cation concentrations were measured during Ca(2+)-free acidic perfusion. [Na+]i was markedly increased to about 44 mmol/l without predisposing to cell damage under these conditions. A marked reduction of cell damage was also afforded under conditions of hypoxia during Ca(2+)- and substrate-free perfusion. Acidosis (pHe = 6.5) under these conditions prevented a lethal increase of [Ca2+]i (2 mumol/l) and partially preserved a negative membrane potential. It is concluded that the predisposition to the Ca2+ paradox is produced by a permeabilisation of gap junction channels at low [Ca2+]e and that upon re-elevation of [Ca2+]e a serious Ca2+ influx proceeds through these leaks.
Diederichs
F
F
Institute of Clinical Biochemistry, Hannover Medical School, Germany.
D000438:Alcohols / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D003080:Cold Temperature; D017629:Gap Junctions / Q000187:drug effects* / Q000378:metabolism*; D006321:Heart / Q000187:drug effects*; D019850:Heptanol; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000378:metabolism; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects* / Q000378:metabolism*; D017136:Ion Transport; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008564:Membrane Potentials; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion; D011092:Polyethylene Glycols / Q000494:pharmacology; D051381:Rats; D012508:Sarcolemma / Q000378:metabolism
D000438:Alcohols; D007473:Ion Channels; D011092:Polyethylene Glycols; D019850:Heptanol; D007770:L-Lactate Dehydrogenase; D002118:Calcium