Skeletal muscle function in hypoxia: effect of alteration of intracellular myoglobin

Enhancement of oxygen flux through myoglobin containing solutions due to myoglobin facilitated oxygen diffusion is well recognized and is most apparent under conditions of hypoxia. To examine the function of intracellular myoglobin in vivo under conditions of hypoxia, the in situ dog gastrocnemius-plantaris muscle was studied. Administration of 10% oxygen resulted in arterial PO2 values between 32 and 36 mm Hg. Muscle oxygen consumption and isometric tension generation were determined during sustained 3-Hz contractions before and after administration of hydrogen peroxide that converted functional myoglobin to forms incapable of reversible combination with oxygen. Muscle blood flow, perfusion pressure, and muscle oxygen delivery were unchanged by such treatment. Hydrogen peroxide administration resulted in oxidation of intracellular myoglobin with a resultant decrease of 37% in muscle oxygen consumption and 42% in tension generation after 20 min of stimulation. In a control group not receiving hydrogen peroxide muscle oxygen consumption and tension generation decreased by 13% and 12%, respectively. We conclude that intact functional myoglobin is important in maintaining muscle function in isometric exercise under conditions of hypoxia.