Influence of simulated ischemia on apoptosis Induction by oxidative stress in adult cardiomyocytes of rats

Oxidative stress may cause apoptosis of cardiomyocytes in ischemic-reperfused myocardium. We investigated whether ischemia-reperfusion modifies the susceptibility of cardiomyocyte induction of apoptosis by oxidative stress. Ischemia was simulated by incubating isolated cardiomyocytes from adult rats in an anoxic, glucose-free medium, pH 6.4, for 3 h. Annexin V-fluorescein isothiocyanate/propidium iodide staining and the detection of DNA laddering were used as apoptotic markers. H2O2 (7.5 mu mol/l) induced apoptosis in 20.1 +/- 1.8% of cells under normoxic conditions but only 14.4 +/- 1.6% (n = 6, P < 0.05) after ischemia-reoxygenation. This partial protection of ischemic-reoxygenated cells was observed despite a reduction in their cellular glutathione content, from 11.4 +/- 1.9 in normoxic controls to 2.9 +/- 0.8 nmol/mg protein (n = 3, P < 0.05). Elevation of end-ischemic glutathione contents by pretreatment with 1 mmol/l N-acetylcysteine entirely protected ischemic-reoxygenated cells against induction of apoptosis by H2O2. In conclusion, ischemia-reperfusion can protect cardiomyocytes against induction of apoptosis by exogenous oxidative stress. This endogenous protective effect is most clearly demonstrated when control and postischemic cardiomyocytes are compared at similar glutathione levels.