K+ ion regulation in retina

Abstract

During onset and offset of illumination, considerable changes in extracellular K+ concentration ([K+]e) occur within particular retinal layers. There are two ways in which glial cells may control [K+]e: (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.Key words: glia, retina, potassium clearance, sodium–potassium pump, potassium channels.