[Interrelations of cyclic adenosine monophosphate and calcium in regulating glycogen synthetase in developing...

The decrease of glycogen synthetase activity under the effect of Ca++ and cAMP is observed in the skeletal muscles of chick embryos only at the later stages of embryogenesis (15-18 days). In the cardiac muscle the activity of glycogen synthetase is inhibited by Ca++ apparently prior to the 12th day of development, long before the effect of cAMP which appears, as in the skeletal muscles, on the 18th day. Under the combined effect of cAMP and Ca++ in vitro and that of Ca++ and epinephrine in vivo, no additivity was observed. The possibility of Ca++ participation in the realization of catecholamine effect on the glycogen synthetase system of muscle and their interrelations with cAMP are discussed.