Myoglobin content and oxygen diffusion: Model analysis of horse and steer muscle

We test the hypothesis that myoglobin is important for O-2 supply near the oxidative capacity of muscle. This hypothesis is evaluated with a simple model that incorporates the properties of heart and skeletal muscle tissue taken from steers and horses exercising at their maximum O-2 consumption rate. These tissue samples allowed us to set the bounds on oxidative demand and O-2 flux from red blood cells to the core of the muscle fiber, to estimate the blood and tissue capacities for O-2 diffusion, and to define the capillary blood Po-2 driving this O-2 flux. A model combining blood convection with tissue diffusion indicates that O-2 diffusion alone is insufficient to achieve the measured O-2 fluxes in many samples. The myoglobin content of these fibers is significantly correlated with this O-2 diffusion limitation and provides sufficient additional O-2 flux to meet muscle O-2 demand. The presence of myoglobin maintains the Po-2 in the fiber core above anoxic levels for the majority of muscles. Thus myoglobin is critical to O-2 supply at fluxes near the maximum and prevents anoxia by maintaining Po-2 above levels needed to support mitochondrial function.