Reversible suppression of skeletal myotube formation in vitro obtained by varying [CO2]

In primary cultures of chicken skeletal muscle, decreasing the [CO2] of the gaseous phase below 10(-3)% resulted in inhibition of cell proliferation and cytolysis. With 10(-3)% CO2-air, cell proliferation was slightly retarded and myotube formation was inhibited approximately 90% compared to cultures receiving 5% CO2-air. Changes in pH were not effective. Culture in low [CO2] resulted in the accumulation of lipoidal inclusions and unique cytoplasmic structures. Increasing time in culture with low [CO2] resulted in an increase in the length of G1 of the cell cycle. The inhibition was reversed by the addition of 5% CO2-air at any time in culture up to 2 wk with a minimum time of 3--6 h required. Lipoidal inclusions decreased in number and the unique cytoplasmic structures were absent. During the first 3 days in culture, myoblasts showing dependence on [CO2] for myotube formation increased in number, and the effect of elevated [CO2] on these cells was long lasting. The data suggest that some aspect of myoblast differentiation relating to cell recognition and fusion is affected by decreased [CO2].