Response properties of the toad retinal pigment epithelium.
Electrophysiologic responses were recorded in vitro from the retina of the toad, Bufo marinus. In the isolated retinal pigment epithelium (RPE)-choroid preparation, a decrease in the K+ concentration outside the apical membrane evoked a sequence of trans-epithelial (TEP) and membrane potential changes. A hyperpolarization originating at the RPE apical membrane that increased the TEP was followed by a delayed hyperpolarization originating at the basal membrane that decreased the TEP. This response sequence differed from the well-studied bullfrog RPE in exhibiting potentials generated at the basal membrane; it more closely resembled responses from the reptilian and avian RPE. The toad direct-current electroretinogram recorded from a neural retina-RPE-choroid preparation also differed from other amphibians and was more similar to responses recorded in reptiles, birds, and mammals. In this initial study, the electrophysiologic characteristics of the RPE's Na+/K+ pump were examined. Contrary to a previous report, ouabain, a specific inhibitor of the pump, depolarized the apical membrane and decreased the TEP. Ba2+ was used to block apical K+ conductance and unmasked a modulation of the Na+/K+ pump by subretinal K+. Decreasing the K+ concentration in the presence of Ba2+ depolarized the apical membrane and decreased the TEP. These responses were blocked by ouabain, indicating that the K+ concentration decrease slowed the Na+/K+ pump.
Griff
E R
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Department of Biological Sciences, University of Cincinnati, Ohio 45221-0006.
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives; D000818:Animals; D001464:Barium; D002024:Bufo marinus; D002829:Choroid / Q000187:drug effects; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D001464:Barium; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium