Control of extracellular potassium levels by retinal glial cell K ⁺ siphoning

Efflux of K⁺ from dissociated salamander Müller cells was measured with ion-selective microelectrodes. When the distal end of an isolated cell was exposed to high concentrations of extracellular K⁺, efflux occurred primarily from the endfoot, a cell process previously shown to contain most of the K⁺ conductance of the cell membrane. Computer simulations of K⁺ dynamics in the retina indicate that shunting ions through the Müller cell endfoot process is more effective in clearing local increases in extracellular K⁺ from the retina than is diffusion through extracellular space.