The retinal pigment epithelium controls the potassium activity in the subretinal space.

The potassium transport of the isolated retinal pigment epithelium from bullfrogs was studied using micropuncture with double barrelled ionselective microelectrodes. Transient changes in intracellular values of electrical potential and potassium activity were monitored in response to abrupt changes in the K+ concentration on the retinal side of the tissue. It is shown, that the transport of potassium in the pigment epithelium depends on the K+ concentration on the retinal side of the tissue in such a way as to keep variations in this concentration at a minimum.