[Myosin and actin levels in poorly differentiated skeletal muscle tumors].

Mouse low-differentiated rhabdomyosarcoma (LD RMS) A7 contains 4.5 mg/cm3 of skeletal muscle type myosin and 9.7 mg/cm3 of actin. When recalculated to a volume of cytoplasm of A7 cells, the myosin concentration increases to 12.5 mg/cm3, while that of actin increases to 27.1 mg/cm3. In skeletal muscles the tissue concentrations of myosin and actin is close to the cytoplasmic concentrations. In mouse femoral muscles the tissue and cytoplasmic concentrations of myosin (approximately 102 mg/cm3) and actin (approximately 67 mg/cm3) are 8 (for myosin) and 2.5 times (for actin) higher than the cytoplasmic concentrations of these proteins in tumour cells. The molar ratio of myosin to actin concentrations is 1:26 in the tumour and 1:8 in the muscles. Possible causes of the absence of skeletal muscle type myofibrils and the manifestations of coordination and discoordination of gene expression in LD RMS cells are discussed.