Sarcoplasmic Reticulum in Duchenne Muscular Dystrophy

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Abstract
Calcium accumulation by isolated sarcoplasmic reticulum (SR) is impaired in Duchenne dystrophy, possible due to a genetic abnormality. We therefore studied the protein and lipid composition of SR membranes. In electron microscopy, the isolated SR fractions appeared normal in Duchenne dystrophy and there was no biochemical or morphological evidence of significant contamination by mitochondria. Electrophoresis of SR proteins and content of major lipids were normal, but phosphatidylcholine was much decreased. However, dystrophic muscle is replaced by connective tissue. Phospholipid analysis suggests that the abnormal composition of dystrophic SR membranes could be due to contamination of the fractions by microsomes from adipose and connective tissue. This might also account for the deficient calcium binding by isolated membranes.