Regional specialization of the membrane of retinal glial cells and its importance to K+ spatial buffering.

Electrophysiological experiments, obtained primarily from dissociated salamander cells, demonstrate that the K+ conductance of Müller cells is distributed in a highly nonuniform manner over the cell surface. A large fraction of the total cell conductance is localized to that portion of the endfoot process that faces the vitreous humor. Along the remainder of the cell, specific K+ conductance is larger in the outer plexiform layer than in neighboring regions. High-endfoot conductance directs K+ spatial buffering currents preferentially through the endfoot process, leading to an efficient form of spatial buffering termed K+ siphoning. Preliminary experiments suggest that the endfeet of astrocytes also have high K+ conductance.