Asymmetrical potassium permeability of the Müller cell. Field potential induced by intraretinal injection of K+-free Ringer's in frog retina.

The field potentials induced by intraretinal injection of K+-free Ringer's were studied in the isolated frog retina. The response to K+-free Ringer's was a positive potential, which was maximum near the depth of injection, and decreased in both directions, proximally and distally. The receptor side was made positive relative to the vitreal side, irrespective of the depth of injection, excepting for the innermost retinal layer bordering the inner limiting membrane. The response at the site of injection and the transretinal potential were dependent upon the depth of injection, being largest when the K+-free Ringer's was injected in or near the inner plexiform layer. Thus, the field potentials induced by K+-free Ringer's were similar in depth profile but opposite in polarity to those induced by high K+-Ringer's. The results were consistent with the previous conclusion that the proximal end region of the Müller cell is far more permeable to K+ than any other part of the cell.