Increase of muscle mitochondrial content with age in murine muscular dystrophy.

Comparison of morphological features of gastrocnemius muscle fibers in normal and dystrophic (dy2J) mice during development was undertaken to determine the time course of increased oxidative capacity in dystrophic fibers. Measurements of mitochondrial volume percent and of Z-line width were made in superficial fast-twitch fibers using electron microscopy and stereological techniques. Dystrophic fibers develop a progressively higher mitochondrial volume percent than normal fibers after 1 month of age. Z-line width is positively correlated with mitochondrial volume percent. The results support the hypothesis that progressive changes in muscle fiber properties result from abnormal neural activity (pseudomyotonia) in dystrophic animals.