Interaction of electron leak and proton leak in respiratory chain of mitochondria — Proton leak induced by superoxide from an electron leak pathway of univalent reduction of oxygen

摘要

By incubating the isolated rat myocardial mitochondria with xanthine-xanthine oxidase, an exogenous superoxide (O_2~(.-)) generating system, and by ischemia-reperfusion procedure of isolated rat heart as an endogenous O_2~(.-) generating system, it was found that both sources of O_2~(.-) showed the same injurious effects on mitochondrial function resulting in (i) increasing proton leak rate, lowering proton pumping activity and H~+/2e ratio of respiratory chain, and (ii) decreasing transmembrane potential of energized mitochondrial inner membrane by succinate oxidation. The injurious effects of O_2~(.-) on these mitochondrial bioenergitical parameters mentioned above exhibited a dosage- or reaction time-dependent mode. O_2~(.-) has no effects on theelectron transfer activity and transmembrane potential of nonenergized mitochondria. Being a superoxide scavenger, 3, 4-dihydroxylphenyl lactate showed obvious protection effects against damage of both exogenous superoxide sources from xanthine-xanthineoxidase system and endogenous O_2~(.-) source from ischemia-reper fused heart on proton pumping activity, H~+/2e ratio and transmembrane potential of energized mitochondria. The experimental results presented here clearly showed that O_2~(.-) radicals induce an increase of proton leak in mitochondria directly related to the molecular mechanism of early phase damage of ischemia-reperfused heart, and also provide evidence to support our recent proposed hypothesis that electron leakage to oxygen to form O_2~(.-) in respiratory chain is one of the mechanical cause of proton leakage in mitochondria.