Rat Skeletal Muscle Cells11This work was supported by Grant No. DRG 10007 from the Damon Ruyon Memorial Fund for Cancer Research, a grant-in-aid from the Muscular Dystrophy Association of America, Inc., and a long-term fellowship from EMBO. The valuable comments and suggestions of Sara Neuman, Erika Krull, H. Dym, G. Lavie, and S. Kaufman during the preparation of this manuscript are gratefully acknowledged.