Effects of extracellular potassium on glycogen stores of astrocytes in vitro.

Astrocyte-enriched and meningeal cell cultures of the rat cerebral cortex were prepared, and their glycogen content was measured after 10-90 min under control (2.5 mM) concentrations of potassium after prefeeding with 20 mM glucose. No net change in glycogen level was noted in either culture over this period. Cell cultures were then exposed to increased concentrations of potassium (5, 10, and 15 mM), and their glycogen content was measured after 10-90 min. Both types of cell culture showed complex and variable changes in glycogen content. In general, increased potassium concentrations caused astrocyte glycogen stores to be reduced at physiological increases of potassium levels (from 2.5 to 5 mM and above), although a period of resynthesis was evident at all potassium concentrations. Meningeal cell glycogen levels were highly variable and only affected by high (10 and 15 mM) levels of potassium. These results are discussed with respect to the theory that changes in the external potassium concentration caused by neuronal activity might act as a signal controlling astrocyte glycogen stores.