K+ ion regulation in retina.

During onset and offset of illumination, considerable changes in extracellular K+ concentration ([K+]c) occur within particular retinal layers. There are two ways in which glial cells may control [K+]c: (1) by space-independent processes, for example, by K+ uptake due to the Na(+)-K+ ATPase, and (2) by space-dependent processes, that is, by spatial buffering currents flowing through K+ channels. Rabbit retinal Müller (glial) cells were studied for expression of mechanisms supporting both kinds of processes. This review demonstrates that rabbit Müller cells have Na-K pumps whose distribution and properties are highly adapted to meet the needs of efficient K+ clearance. Furthermore, spatial buffering currents through specialized K+ channels of Müller cells greatly accelerate retinal K+ clearance during and after stimulation.