The effect of cholecalciferol in vivo on proteins and lipids of skeletal muscle from rachitic chicks.

The protein and lipid constituents of skeletal muscle subcellular fractions isolated from chicks fed a vitamin D-deficient diet for 3 weeks and chicks replated with cholecalciferol (vitamin D3) were analyzed. Administration of the sterol markedly altered the protein composition of mitochondria. The changes were localized in the inner membranes and consisted of a modification of the relative amounts of proteins of approximate mol wt of 83,000, 58,000, 42,000, and 34,000. In addition, treatment with vitamin D3 modified the distribution pattern of components of the actomyosin contractile complex. An increase in actin and troponin C was particularly noticeable. No differences between rachitic and treated animals were detected in the protein composition of sarcoplasmic reticulum membranes and postmicrosomal soluble fraction. A significant increase in the phospholipid content of sarcoplasmic reticulum (P less than 0.05), and to a lesser extent of mitochondria, was observed in repleted chicks. The relative proportions of individual phospholipids, however, were not changed. Injection of an acute dose of cholecalciferol to chicks less severely depleted in vitamin D significantly stimulated the incorporation of 32PO4 in vivo to muscle homogenates, mitochondria, and sarcoplasmic reticulum (P less than 0.05). As the increases in specific activities of sarcoplasmic inorganic P and membrane lipid P were similar whereas that of serum remained unchanged, the results are compatible with the idea that vitamin D3 stimulates phosphate fluxes across muscle membranes. The sterol produced minor modifications in the fatty acid composition of sarcoplasmic reticulum (P less than 0.05).