Extracellular K+ activity changes related to electroretinogram components. II. Rabbit (E-type) retinas.

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Abstract
Electroretinogram (ERG) and extracellular K+ activity (Ko+) measurements were carried out in isolated superfused rabbit eyecup preparations under control conditions and during the application of pharmacological agents that selectively modify the light-responsive retinal network. Light-evoked Ko+ changes in the rabbit (E-type) retina resemble those previously described in amphibian (I-type) retinas. Different components of the light-evoked Ko+ changes can be distinguished on the bases of retinal depth, V vs. log I properties, and their responses to pharmacologicl agents. Two separable sources of light-evoked increases in extracellular K+ were found: a proximal source and a distal source. The properties of the distal light-evoked Ko+ increase are consistent with the hypothesis that it initiates a K+-mediated current through Mueller cells that is detected as the primary voltage of the electroretinographic b-wave. Both the corneal-positive component of c-wave and the corneal-negative slow PIII potential apparently result from K+-mediated influences on, respectively, the retinal pigment epithelium and Mueller cells.