Regional specialization of retinal glial cell membrane

Abstract

Neural activity generates increases in extracellular K⁺ concentration, [K⁺]₀, which must be regulated in order to maintain normal brain function¹. Glial cells are thought to play an important part in this regulation through the process of K⁺ spatial buffering^2–4: K⁺-mediated current flow through glial cells redistributes extracellular K⁺ following localized [K⁺]₀ increases. As is the case in other glia, the retinal Müller cell is permeable almost exclusively to K⁺ (ref. 5). Recent experiments^6–8 have suggested that this K⁺ conductance may not be distributed uniformly over the cell surface. In the present study, two novel techniques have been used to assess the Müller cell K⁺ conductance distribution. The results demonstrate that 94% of all membrane conductance lies in the endfoot process of the cell. This strikingly asymmetric distribution has important consequences for theories concerning K⁺ buffering and should help to explain the generation of the electroretinogram.