Fig. 2.

Diagram depicting the role of glial cells in [K⁺]_o homeostasis. Top: Glial cells are electrically coupled via gap junctions forming a functional syncytium. With [K⁺]_o equaling 3 mM, the glial syncytium has a membrane potential of approximately −90 mV. (A) Net K⁺ uptake mechanism. When [K⁺]_o is increased, glial cells accumulate K⁺ either by the activity of a Na,K–ATPase or by a pathway in which K⁺ is cotranported with Cl⁻. In this mechanism of [K⁺]_o regulation, the membrane potential in the glial syncytium is spatially uniform at −56 mV. (B) K⁺ spatial buffering mechanism. Local increases of [K⁺]_o produce a glial depolarization that spreads through the glial syncytium. The local difference in Vm and E_Kdrives the K⁺ uptake in regions of elevated [K⁺]_o and K⁺ outflow at distant regions. The intracellular currents are carried by K⁺ and extracellular currents are mediated by other ions such as Na⁺. [From Orkand (1986), with permission.]