Morphometric studies of normal muscle mitochondria.

The study describes mitochondrial morphometry in normal adult limb muscles of various mammalian species. The size, area, shape, and volume of mitochondria were compared in two regions (subsarcolemmal and intermyofibrillary) and fiber types (type 1 and type 2) of the 1) human and monkey quadriceps, 2) cat soleus and caudofemoralis-CF, and 3) rat soleus and extensor digitorum longus-EDL. The Z band width showed distinct differences between the two types of fibers in all muscles. The mitochondrial size and volume varied in different muscles but the shape remained oval throughout. The human quadriceps mitochondria were the smallest in size and volume. The monkey and rat muscles showed higher mitochondrial volume which was not significantly different between the two fiber types. The cat soleus and EDL muscles showed significant difference in the mitochondrial volume of two fiber types and also significant correlation between the Z band width and the mitochondrial volume, the soleus being pure type 1 fibers and the EDL being pure type 2B fibers. We conclude that only the shape of mitochondria, but not the size and volume, is independent of the species, the type of muscle and the region of a fiber.