Regulation of glycogen content in primary astrocyte culture: effects of glucose analogues, phenobarbital, and methionine sulfoximine.

Compounds known to affect glycogen metabolism in vivo or in cell-free preparations were used to investigate the regulation of glycogen content in intact astrocytes cultured from newborn rat cortex. Compounds were added with fresh medium to culture dishes, and astrocyte glucose and glycogen content determined 24 h later. Increasing the medium glucose concentration from 7.5 mM to 30 mM increased cell glycogen content 80%. Addition of 2-deoxyglucose or 3-O-methyl glucose (2.5-10 mM) also increased cell glycogen content, 50-100%, suggesting a regulatory rather than mass action effect of glucose on astrocyte glycogen content. The phosphorylase b inhibitors 2,2',4,4',5,5'-hexabromobiphenyl and riboflavin had no effect on astrocyte glycogen content, consistent with negligible phosphorylase b activity in normal astrocytes. Phenobarbital and L-methionine-DL-sulfoximine (MSO) are both known to induce astrocyte glycogen accumulation in vivo. The addition of phenobarbital (2 mM) had no effect on the glycogen content of cultured astrocytes, suggesting an indirect mechanism for the in vivo effect. MSO at 1 mM, however, induced a 300% increase in glycogen content. The time course of glucose and glycogen content after MSO administration suggests this increase to be the result of slowed glycogenolysis rather than accelerated glycogen synthesis.