Nitric oxide regulates oxygen uptake and hydrogen peroxide release by the isolated beating rat heart

Isolated rat heart perfused with 1.5-7.5 mu M NO solutions or bradykinin, which activates endothelial NO synthase, showed a dose-dependent decrease in myocardial O-2 uptake from 3.2 +/- 0.3 to 1.6 +/- 0.1 (7.5 mu M NO, n = 18, P < 0.05) and to 1.2 +/- 0.1 mu M O-2 . min(-1). g tissue(-1)(10 mu M bradykinin, n = 10, P < 0.05). Perfused NO concentrations correlated with an induced release of hydrogen peroxide (H2O2) in the effluent (r = 0.99, P < 0.01). NO markedly decreased the O-2 uptake of isolated rat heart mitochondria (50% inhibition at 0.4 mu M NO, r = 0.99, P < 0.001). Cytochrome spectra in NO-treated submitochondrial particles showed a double inhibition of electron transfer at cytochrome oxidase and between cytochrome b and cytochrome c, which accounts for the effects in Oa uptake and H2O2 release. Most NO was bound to myoglobin; this fact is consistent with NO steady-state concentrations of 0.1-0.3 mu M, which affect mitochondria. In the intact heart, finely adjusted NO concentrations regulate mitochondrial O-2 uptake and superoxide anion production (reflected by H2O2), which in turn contributes to the physiological clearance of NO through peroxynitrite formation.