Myoglobin function and energy metabolism of isolated cardiac myocytes: effect of sodium nitrite

Inactivation of intracellular myoglobin by sodium nitrite or by carbon monoxide in isolated cardiac myocytes diminishes steady-state respiratory rate and phosphocreatine concentration (PCr) by approximately 25% at nonlimiting oxygen pressures; oxidative phosphorylation and glycolysis together are insufficient to maintain ATP, and PCr falls. At concentrations required to convert myoglobin to high-spin ferric myoglobin, nitrite does not affect the respiration of isolated aerobic heart mitochondria. The creatine phosphokinase-catalyzed equilibrium between PCr and ATP is not affected by nitrite. Myoglobin inactivation reduces PCr in cells in which glycolytic ATP production is blocked by iodoacetate. However, inhibition of electron transport by rotenone does block myoglobin-mediated oxygen uptake. These data suggest that functional myoglobin augments mitochondrial oxidative phosphorylation [myoglobin-mediated oxidative phosphorylation (30)]. Myoglobin itself does not cross mitochondrial membrane(s). At high oxygen pressures used here, myoglobin is everywhere saturated with oxygen, and facilitated oxygen diffusion vanishes. Oxidative phosphorylation must be augmented by some effector, such as NADH or a carrier of reducing or oxidizing equivalents that can transduce the effect of oxymyoglobin across the mitochondrial membrane(s).