Potassium Homeostasis in Glia

Diverse cellular mechanisms exist in the central nervous system to counteract rapid changes in extracellular K+ concentration that occur with neuronal activity. These mechanisms of K+ buffering include net K+ uptake into glial cells and K+ spatial buffering by glia. With net K+ uptake, K+ influx into glial cells occurs via activity of the Na, K-ATPase pump and by ion flux through Na–K–Cl cotransporters. With K+ spatial buffering, regulation of local K+ changes occurs by a K+ current flow through glial cells, transferring K+ from areas of high concentration to areas of low concentration. A specialized form of K+ spatial buffering, termed K+ siphoning, occurs in the retina, where K+ currents are directed preferentially through cell end feet.