Relationship between mitochondrial volume density and capillarity in hamster muscles

Mitochondrial volume density and lipid droplet-volume density were stereologically determined from electron micrographs of muscle fibers from three hamster muscles: retractor, sartorius, and soleus. The number of capillaries around a fiber, length of capillary-fiber contact, and muscle fiber area were also measured. Glycolytic fibers of the retractor and sartorius had larger cross-sectional areas, lower mitochondrial-volume densities, fewer subsarcolemmal aggregates of mitochondria, and lower capillary-fiber contact length in comparison to oxidative fibers of the retractor and soleus. Values for mitochondrial volume density in the different muscles correlated well (r = 0.97) with resting O2 consumption. The mitochondrial volume densities for each muscle correlated well (r = 0.99) with O2 diffusion coefficients of these muscles. Our results indicate that an analysis of the adequacy of O2 supply to an individual muscle fiber must take into account an interplay among fiber size, percent of the muscle fiber perimeter in contact with a capillary (capillary-fiber contact), and O2 demand of the fiber estimated by mitochondrial volume density.