The Journal of General Physiology, Vol 70, 405-425, Copyright © 1977 by The Rockefeller University Press
Potassium and the photoreceptor-dependent pigment epithelial hyperpolarization
B Oakley 2d
Light-evoked changes in pigment epithelial cell membrane potentials and
retinal extracellular potassium ion concentration, [K+]0, were measured in
an in vitro frog retina-pigment epithelium-choroid preparation. Light
stimuli hyperpolarized the apical membrane of the pigment epithelium.
Through an electrical shunt pathway connecting the apical and basal
membranes, the basal membrane also hyperpolarized, but to a lesser degree
than the apical membrane. This differential hyperpolariation of the two
membranes increased the transepithelial potential (TEP). This increase in
TEP was shown to be the major voltage source of the c-wave of the
electroretinogram (ERG). Direct measurement of [K+]0 in the distal retina,
made with K+-specific microelectrodes, showed a light-evoked decrease in
[K+]0 having an identical time course to the apical hyperpolarization.
There was a linear relationship between the light-evoked change in TEP and
the logarithm of [K+]0. This exact relationship was also found when the
apical membrane was perfused directly with solutions of varying [K+]0. The
change in TEP associated with the ERC c-wave, therefore, was explained
solely by the response of the pigment epithelium to the light-evoked
decrease in [K+]0 in the distal retina.
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