Normal function in sarcoplasmic reticulum from mice with muscular dystrophy.

A rapid, gentle technique has been developed for the isolation of sarcoplasmic reticulum (SR) from small amounts of skeletal muscle from normal and dystrophic mice. Assays for mitochondrial and surface membrane marker enzymes revealed only low levels of contamination in the isolated fractions. A small amount of calcium-insensitive ("basal") ATPase in the normal preparation and a higher value in the dystrophic were shown to be due to contamination by a lighter membrane fraction of probable surface membrane origin. Isolated SR from normal and dystrophic mice were indistinguishable by thin section and freeze-fracture electron microscopy. Only small differences in calcium loading rates and capacity, and in calcium-stimulated ATPase activity, were present. These were attributable to small differences in purity. We conclude that there is no difference in SR from normal and dystrophic mice in the properties measured.