[Extracellular potassium in the frog retina and its light-induced changes]

Similar downhill gradients of [K]0 were revealed in the aspartate--treated dark--adapted frog retina and in the eye cup without aspartate. [K]0 in the receptor layer is 8 X 10(-3) M, while in the proximal retina it is nearly 2.7 X 10(-3) M. Illumination decreased [K]0 in the receptor layer to 2.5 X 10(-3) M. The dark level and the light-induced changes of [K]0 were practically unaltered when Ba2+ ions suppressed the slow PIII and the resting transretinal glia potential blocking up the Müller cells permeability for K+. The findings suggest that [K]0 around the receptor space is regulated by red rods with no interference from the Müller cells or pigment epithelial cells. The amplitude of [K]0 changes seems to be physiologically significant.