Differing Populations of Mitochondria Isolated from the Skeletal Muscle of Normal and Dystrophic Hamsters

Abstract

Polarographic studies of a magnesium-responsive, calcium-associated defect of oxidative phosphorylation in dystrophic hamster skeletal muscle suggested that all dystrophic mitochondria are defective. This is at variance with the typical histological picture of dystrophic muscle, which shows, besides defective muscle fibers, many apparently normal cells, with presumably normal mitochondria. This discrepancy was resolved by linear sucrose density-gradient centrifugation (39–51%, w/v), which can separate normal mitochondria from calcium-loaded organelles. Upon density-gradient centrifugation of control and dystrophic muscle mitochondria, both preparations were found to yield suspended bands of similar density. However, the dystrophic preparations also produced a pellet at the bottom (most dense region) of the tube with calcium levels 10–40 times higher than those in the suspended bands. The data show the existence in dystrophic muscle of a distinct population of mitochondria with very high calcium levels that is absent from normal preparations. During the course of oxidative phosphorylation measurements, loss of calcium from these particular organelles and its uptake by others appear to render all the mitochondria defective. This exchange can be prevented by ruthenium red. Density-gradient centrifugation allows the identification of dystrophic muscle mitochondria in early and/or mild disease stages in which polarographic testing of mitochondria isolated by conventional centrifugation fails to detect an abnormality.