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 ac tion potential was investigated in isolated adult rat cardiac myocytes . Superfusion with H2O2 led to a decrease in the energy charge and dep letion of nonprotein thiols and elicited hypercontracture of the myocy tes. Treatment with 3-aminobenzamide (3-AB), an inhibitor of protein r ibosylation, increased the lifetime of H2O2-exposed myocytes and atten uated depletion of ATP and nonprotein thiols. H2O2-mediated DNA strand breaks were increased in the presence of 3-AB. On exposure to H2O2, m yocytes 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+ cur rents (I-K,I-ATP). The late decrease in APD was inhibited by glibencla mide (which inhibits I-K,I-ATP), but the initial prolongation of the a ction potential was exacerbated. Treatment with 3-AB or recordings wit h 10 mM ATP in the patch pipette caused an initial delay in the expres sion of H2O2-induced changes, but later caused a more pronounced and s ustained increase in APD. These interventions delayed the activation o f I-K,I-ATP Thus enhanced ribosylation (presumably due to activation o f DNA repair) appears to be a significant source of ATP depletion unde r oxidative stress that, via activation of I-K,I-ATP, mediates oxidati ve modifications in the action potential.