Differential inhibitory action of nitric oxide and peroxynitrite on mitochondrial electron transport

Various authors have suggested that nitric oxide ((NO)-N-.) exerts cytotoxic effects through the inhibition of cellular respiration, Indeed, in intact cells (NO)-N-. inhibits glutamate-malate (complex I) as well as succinate (complex II)-supported mitochondrial electron transport, without affecting TMPD/ascorbate (complex IV)-dependent respiration. However, experiments in our lab using isolated rat heart mitochondria indicated that authentic (NO)-N-. inhibited electron transport mostly by reversible binding to the terminal oxidase, cytochrome a(3), having a less significant effect on complex II- and no effect on complex I-electron transport components. The inhibitory action of (NO)-N-. was more profound at lower oxygen tensions and resulted in a differential spectra similar to that observed in dithionite-treated mitochondria. On the other hand, continuous fluxes of (NO)-N-. plus superoxide (O-2(.-)), which lead to formation of micromolar steady-state levels of peroxynitrite anion (ONOO-), caused a strong inhibition of complex I- and complex II-dependent mitochondrial oxygen consumption and significantly inhibited the activities of succinate dehydrogenase and ATPase, without affecting complex IV-dependent respiration and cytochrome c oxidase activity. In conclusion, even though nitric oxide can directly cause a transient inhibition of electron transport, the inhibition pattern of mitochondrial respiration observed in the presence of peroxynitrite is the one that closely resembles that found secondary to (NO)-N-. interactions with intact cells and strongly points to peroxynitrite as the ultimate reactive intermediate accounting for nitric oxide-dependent inactivation of electron transport components and ATPase in living cells and tissues. (C) 1996 Academic Press, Inc.