Myoglobin-dependent oxidative metabolism in the hypoxic rat heart

The role of myoglobin in facilitating O2 diffusion for oxidative energy production was investigated at high (0.9 mM) and low (0.1 mM) O2 tensions in the Langendorff-perfused rat heart. 31P nuclear magnetic resonance was used to monitor the intracellular pH and concentrations of high energy phosphates. NaNO2 or phenylhydrazine was used to inactivate greater than 85% of intracellular myoglobin. During hypoxia, ATP and phosphocreatine were depleted significantly more rapidly in hearts with reduced concentrations of functional myoglobin than in control hearts. However, at 0.9 mM O2, myoglobin inactivation did not limit oxidative energy metabolism. It is concluded that facilitation of O2 diffusion by cardiac myoglobin plays a significant role in O2 delivery to the mitochondria at low O2 tensions.