Effects of insulin, methoxamine, and calcium on glycogen synthase in rat adipocytes
Lawrence, J.C.; Larner, J.
Molecular Pharmacology 14(6): 1079-1091
1978
ISSN/ISBN: 0026-895X PMID: 215895 Document Number: 137481
Inactivation of glycogen synthase by methoxamine was not associated with changes in cyclic decreased the percentage of glycogen synthase I activity in the presence of, but not the absence of calcium. When A23187 and methoxamine were added together, no further decrease in the percentage of glycogen synthase I activity was observed below that produced by either agent alone. The activation of glycogen synthase by insulin was not diminished by incubating cells in Ca-free medium plus 1 mM EGTA. An effect of insulin on glycogen synthase was observed even in the presence of A23187. The increase in the percentage of glycogen synthase I activity due to insulin is apparently independent of extracellular Ca. Adrenergic receptor stimulation may lead to a decrease in the percentage of glycogen synthase I activity by increasing the concentration of cytosolic Ca. If the activation of glycogen synthase involves Ca, presumably insulin would act by decreasing cytosolic Ca since the effects of insulin on glycogen synthase are opposite to those of methoxamine and A23187.