UNCOUPLING OF MITOCHONDRIAL OXIDATIVE-PHOSPHORYLATION ALTERS LIPID PEROXIDATION-DERIVED FREE-RADICAL PRODUCTION BUT NOT RECOVERY OF POSTISCHEMIC RAT HEARTS AND POSTHYPOXIC ENDOTHELIAL-CELLS

The contribution of mitochondrial free radical production towards the initiation of lipid peroxidation (LPO) and functional injury in the po st-ischemic heart is unclear. Using the isolated rat heart model, the effects of the uncoupler of mitochondrial oxidative phosphorylation di nitrophenol (DNP, 50 mu M final) on post-ischemic lipid peroxidation-d erived free radical production and functional recovery were assessed. Hearts were subjected to 30 min total global ischemia followed by 15 m in of reperfusion in the presence of DNP. As expected, DNP enhanced ox ygen consumption before (11.3+/-0.9 mu mol/min, p < 0.001) and during reperfusion (at 10 min: 7.9+/-0.7 mu mol/min), compared to the heart w ith control treatment (8.2+/-0.5 and 6.7+/-0.3, respectively). This ef fect was only associated with a higher incidence of ventricular tachyc ardia during reperfusion (80 vs. 50% for control treatment, p < 0.05). Electron spin resonance spectroscopy (ESR) and spin trapping with alp ha-phenyl-tert-butylnitrone (PBN, 3 mM final) were used to monitor fre e radical generation during reperfusion. The vascular concentration of PBN-radical adducts (untreated: 6.4+/-1.0 nM, at 10 min) decreased in the presence of DNP (1.7+/-0.4 nM, p < 0.01). The radical concentrati on inversely correlated with myocardial oxygen consumption. Total libe ration of free radical adducts during the initial 10 min of reperfusio n was reduced by DNP (0.59+/-0.09 nmol, p < 0.01) compared to the resp ective control treatment (1.26+/-0.16 nmol). Similar effects, preventi on of PBN adduct formation and unchanged viability in the presence of DNP, were obtained with endothelial cells during post-hypoxic reoxygen ation. Since inhibition of mitochondrial phosphorylation can inhibit t he formation of LPO-derived free radicals after an ischemic/hypoxic in terval, mitochondria may represent an important source of free radical s capable of initiating lipid peroxidative injury during reperfusion/r eoxygenation.