Glycogen metabolism in bovine adrenal medulla

Glycogen content was determined both in whole adrenal medullary tissue and in isolated adrenal chromaffin cells, in which it responds to glucose deprivation and restoration. [14C]glucose incorporation into glycogen in isolated adrenal chromaffin cells is increased by previous glucose deprivation ("fasting"). Total glycogen synthase activities are 452 +/- 66 mU/g in whole tissue and 305 +/- 108 mU/g in isolated cells. The Km of glycogen synthase for UDP-glucose is 0.67 mM with 13 mM glucose-6-phosphate and 1 mM without this effector. The in vitro inactivation process of glycogen synthase a has been found to be mainly cyclic AMP-dependent, but it also responds to Ca2+. Total glycogen phosphorylase activities are 8.69 +/- 1.26 U/g in whole tissue and 2.38 +/- 0.30 U/g in isolated cells. The requirements for interconversion in vitro of both glycogen synthase and phosphorylase suggest a system similar to that of other tissues. During incubation of isolated adrenal chromaffin cells with 5 mM-glucose, phosphorylase a activity decreases and synthase a activity increases; these changes are more marked in "fasted" cells. Glycogen content and glycogen synthase and phosphorylase activities are higher in the adrenal medulla than in the brain, suggesting a greater metabolic role of glycogen in the adrenal medulla.