Contribution of ATP to oxidative stress-induced changes in action potential of isolated cardiac myocytes.

The role of ATP in oxidative stress-mediated changes in the cardiac action potential was investigated in isolated adult rat cardiac myocytes. Superfusion with H2O2 led to a decrease in the energy charge and depletion of nonprotein thiols and elicited hypercontracture of the myocytes. Treatment with 3-aminobenzamide (3-AB), an inhibitor of protein ribosylation, increased the lifetime of H2O2-exposed myocytes and attenuated depletion of ATP and nonprotein thiols. H2O2-mediated DNA strand breaks were increased in the presence of 3-AB. On exposure to H2O2, myocytes patch clamped with 1 mM ATP in the pipette initially displayed prolonged action potential durations (APD), which were later markedly abbreviated and accompanied by the activation of ATP-sensitive K+ currents (I(K,ATP)). The late decrease in APD was inhibited by glibenclamide (which inhibits I(K,ATP)), but the initial prolongation of the action potential was exacerbated. Treatment with 3-AB or recordings with 10 mM ATP in the patch pipette caused an initial delay in the expression of H2O2-induced changes, but later caused a more pronounced and sustained increase in APD. These interventions delayed the activation of I(K,ATP). Thus enhanced ribosylation (presumably due to activation of DNA repair) appears to be a significant source of ATP depletion under oxidative stress that, via activation of I(K,ATP), mediates oxidative modifications in the action potential.