Myocyte deenergization and intracellular free calcium dynamics.
Intracellular free calcium in adult rat heart ventricular myocytes was monitored by single cell fura-2 fluorescence microscopy. The average resting free calcium in rod-shaped quiescent cells was 125 nM (range 70-200 nM). When cells were deenergized with an inhibitor (amytal) and an uncoupler (carbonyl-cyanide m-chlorophenylhydrazone) of oxidative phosphorylation, there was a small but significant increase (125-380 nM) in intracellular free calcium during the transition to a highly contracted (square) rigor form. After the onset of contracture, which occurred 5-15 min after addition of the above compounds, the increase in free calcium was slow for the first 20 min, reaching a value of only 750 nM. Thereafter, the rate of increase accelerated and 50 min after contracture, free calcium was approximately 3 microM. The increase in free calcium was absolutely dependent on extracellular calcium but was not inhibited by high concentrations of verapamil (2-7 microM), suggesting influx via the Na+-Ca2+ exchange transporter as the cause of calcium increase. However, in calcium repletion protocols the rate of increase in sodium-loaded myocytes was greatly accelerated if cells were not depleted of ATP, confirming suggestions that ATP loss partially inhibits Na+-Ca2+ exchange.
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Department of Physiological Chemistry, Ohio State University, Columbus 43210.
Altschuld
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Stokes
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D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004734:Energy Metabolism; D016257:Fura-2; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains
D001572:Benzofurans; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000255:Adenosine Triphosphate; D002118:Calcium; D016257:Fura-2