HORMONAL REQUIREMENTS FOR MYOGENESIS OF STRIATED MUSCLE IN VITRO: INSULIN AND SOMATOTROPIN

Abstract

The development of muscle in vitro from embryonic presumptive myoblasts is known to have complex nutritional requirements.' One of the necessary ingredients for myogenesis in vitro, and indeed for the growth of many cell types, is serum. During the course of studies aimed at understanding the mechanisms involved in the fusion of myoblasts, it became of interest to delete serum from the medium and to determine whether myogenesis could be restored by the addition of known factors. In view of the fact that muscle is dependent upon insulin for its normal function,2 this hormone was introduced into the culture medium in the absence of serum. It was observed that myotube formation was restored, although not to the extent obtained if serum were present. When somatotropin and insulin were both added to replace serum, an even greater degree of myotube formation took place. This report is therefore concerned with the effects of insulin and somatotropin on myogenesis. Materials and Methods-Materials: Crystalline bovine insulin and bovine somatotropin (1 IU/mg) were purchased from the Sigma Chemical Company. Highly purified collagenase, free of noncollagen proteolytic activity, was purchased from the Worthington Biochemical Company. Four-times-recrystallized bovine serum albumin was purchased from the Nutritional Biochemicals Corporation. Stock solutions were prepared by dissolving insulin at a concentration of 0.5 mg/ml in 0.001 N HCl, 0.1% NaCl, and somatotropin at the same concentration in 0.02 M potassium