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[Effects of A23187 and cytochalasin B on proliferation and differentiation of the cultured myoblasts].

The effects of A23187 (a substance acting on cell membrane) and cytochalasin B (a substance acting on cell structure) on the growth and differentiation of myoblasts (L6 cell) were examined using a cultured system. The L6 cells (1 x 10(5)) were incubated for 10 days in DMEM medium containing 10% fetal calf serum (a growth medium) by exchanging the medium every 3rd day. They showed no morphological differentiation and no increase in creatine kinase activity, myoglobin content and Ca2+ concentration. However, when L6 cells were incubated in DMEM medium containing 2% horse serum and 6 micrograms/ml insulin (an incubation medium for differentiation), they were morphologically differentiated into the myotube after 6-day culture with increase in creatine kinase activity, myoglobin content and Ca2+ concentration. In the presence of 40 nM A23187, no marked morphological change was observed in the L6 cells as compared with the control, but the myoglobin level rapidly increased to 18.2 x 10(-2) ng/micrograms (4.2-fold value of the control) at 10-day culture. In the presence of 200 nM cytochalasin B, there was no morphological change in the L6 cells, and no increase in the levels of creatine kinase and myoglobin. These data suggest that the function of the cell membrane and intracellular Ca2+ concentration play important roles in differentiating the muscle cells, because A23187 promotes biochemical differentiation of L6 cells as shown by increased myoglobin content.