Glial cell function: Active control of extracellular K⁺ concentration

To investigate the ability of the glial cell to control the extracellular K⁺ ion concentration in the CNS 3 kinds of experiment were carried out. (1) The ability of isolated cell fractions enriched in glia or neurons to reaccumulate K⁺ was measured. (2) The activation of the Na⁺K⁺-ATPase by K⁺ was measured on these isolated cell suspensions. (3) Plasma membrane fractions were prepared from neurons and glia and the Na⁺K⁺-ATPase activity was studied as a function of K⁺ ion concentration. The glial cell Na⁺K⁺-ATPase was always more active, approximately 2.5- to 4-fold, and markedly more sensitive to variations in the K⁺ ion concentration than the neuronal ATPase. These results support the idea that control of the extracellular K⁺ ion concentration in the CNS is at least in part dependent on the metabolically coupled sodium-potassium pump of the glial cell.