Divergent syntheses of actin and myosin infused and unfused muscle cells

Hormone responsiveness of adenylate cyclase activity of cultured myogenic cells

We studied the effect of catecholamines on the adenylate cyclase activity of myogenic cells of the L6 line during the differentiation process. The enzyme of mononucleated myoblasts was found to be activated by adrenaline L, noradrenaline L, and to a small extent, by adrenaline D and dihydrocymandelic acid. The adenylate cyclase of the differentiated cells responded to adrenaline L and noradrenaline L but not to adrenaline D or dihydroxymandelic acid. This activation could be inhibited by the addition of DOPA and propranolol, a specific beta adrenergic blocker. alpha adrenergic compounds such as phentolamine did not have any effect. It is concluded that beta adrenergic receptors are present on myogenic cells before and after differentiation.

Gene expression during the differentiation of myogenic cells of the L6 line

The problem of the mechanistic relationship among the different phenotypic expressions in an established myogenic line was approached by blocking cell fusion at different developmental stages, by addition of cytochalasin B. The addition of the drug to cultures at the time when the first two myotubes appeared on the dish, blocked fusion, but did not affect DNA synthesis, expression of myosin, phosphorylase, phosphocreatine kinase, phosphorylase kinase or glycogen synthetase, nor the organization of the elements of the hexagonal lattice. It is concluded that cell fusion is not a prerequisite for the expression of the differentiated phenotype.