Effects of hydrogen peroxide on action potentials and intracellular Ca2+ concentration of guinea pig heart

Oxygen free radicals and Ca2+ overload have been implicated in the genesis of reperfusion induced arrhythmia and injury. Effects of hydrogen peroxide (H2O2) on action potentials and intracellular Ca2+ concentration ([Ca2+]i) were studied using guinea pig papillary muscles and ventricular myocytes. High concentration of H2O2 (10 mmol.litre-1) caused delayed afterdepolarisations in all six papillary muscles, and induced triggered activity in 3/6 preparations. Pretreatment with ryanodine (1 mumol.litre-1) abolished delayed afterdepolarisations and triggered activity induced by H2O2. [Ca2+]i and morphological changes in isolated ventricular myocytes of guinea pig were measured using fura-2. Quiescent and rod shaped myocytes became shortened and rounded (contracture) after the application of 0.1 and 1 mmol.litre-1 H2O2. [Ca2+]i increased from the control values of 53 (SEM 4) and 62(8) nmol.litre-1 to 110(29) and 105(24) nmol.litre-1 (p less than 0.05 v control) when cells were shortened during perfusion with 0.1 and 1 mmol.litre-1 H2O2, respectively. The values were 130(26) nmol.litre-1 (p less than 0.05 v control) and 100(18) nmol.litre-1 (p less than 0.05 v control) when the cells became rounded during perfusion with 0.1 and 1 mmol.litre-1 H2O2. We suggest that the arrhythmia caused by Ca2+ overload was induced by H2O2, possibly by lipid peroxidation of cell membrane. H2O2 was also shown to shorten cells and cause cell contracture (rounding). The mechanism of cell injury is not likely to be due to the Ca2+ overload, since the increase in [Ca2+]i during perfusion with H2O2 was not large.