Efflux of potassium from the isolated frog retina: a study of the photic effect.

1. Illumination of the isolated frog retina reduces the efflux of (42)K (and (86)Rb).2. Perfusion with a solution containing glutamate ions does not abolish the effect, although the electroretinogram is modified and the b-wave absent in this condition.3. Perfusion with a solution with only 2.36 mM sodium abolishes the effect of light on the efflux of potassium (and rubidium).4. The amplitude of the photic effect, measured in the first 2 min of illumination, is in linear proportion with the logarithm of the concentration of extracellular sodium ions.5. A steady rate of absorption of a few quanta per rod and per second yields a just detectable effect on the efflux of potassium (and rubidium).6. Strong illuminations followed by darkness reduce the efflux of rubidium for a period of time roughly comparable to the time of dark adaptation.7. The interpretation is proposed that the photoreceptor cells (and possibly other retinal cells too) cause the effect, and that the retention of potassium induced by light is secondary to the hyperpolarization of their membrane.