Changes in adenylate cyclase, cyclic AMP, and protein kinase levels in chick myoblasts, and their relationship to differentiation

Abstract Examination of components of the cAMP system in primary cultures of differentiating chick myoblasts revealed a basal intracellular cAMP level of 50–100 pmole/mg of DNA, which increased ten to fifteen-fold for approximately 1 hr between 37.5 and 39.5 hr of culture, only 5–6 hr before the initiation of myoblast fusion. Activities of the enzymes adenylate cyclase and protein kinase were examined during the initial stages of myoblast differentiation. Both the basal activity and the degree of NaF stimulation of adenylate cyclase increased during the time examined, the appearance of these changes coinciding in time of culture with the observed peak of cAMP. The protein kinase present was sensitive to cAMP, and its basal and cAMP stimulated activities increased throughout the prefusion period of culture. The results suggest a causal relationship between the increase in adenylate cyclase activities, the increase in intracellular cAMP, and the onset of fusion; and the possibility that intracellular cAMP levels control the expression of myoblast differentiation is discussed.