Perfusion of hearts with DETA/NO partially prevents the ischemia-induced decrease in respiratory chain activity and increase in proton leak of subsequently isolated mitochondria. (A): kinetics of the respiratory chain activity, and (B): kinetics of proton leak. Rat hearts were perfused for 3 min with 50 μM of DETA/NO, then ischemia was induced for 30 min. Isolated mitochondria were placed in a vessel with incubation buffer A (see Methods) and their oxygen consumption and membrane potential were measured simultaneously. 5 mM succinate (plus 1 μM rotenone) was used as respiratory substrate. Kinetics of the respiratory chain was determined as the dependence of the mitochondrial respiration rate on the membrane potential by titrating with carboxyatractyloside (0.4–8.0 nmol/mg mitochondrial protein). The kinetics of the proton leak was measured in the presence of excess oligomycin (1 μg/mg protein), mitochondrial respiration and membrane potential were titrated with malonate (0.33–6 mM). Means ± standard errors of 5 separate experiments are presented.