Light-induced potassium fluxes in the skate retina.

Changes in the extracellular concentration of potassium [K+]0 in response to photic stimulation were studied in the skate retina with the aid of ion-selective electrodes. The results confirm earlier studies in demonstrating that the light-evoked changes originate at three intraretinal sites; an efflux of K+ was recorded in the regions of the two plexiform (synaptic) layers, whereas a decrease in [K+]0 occurred in the extracellular space surrounding the photoreceptors. Prolonged illumination induced long-term alterations in the levels of [K+]0 which, depending upon the retinal depth of the recording electrode, contained contributions from the various sinks and sources of [K+]0. In addition, the marked undershoot of the baseline level of [K+]0 that followed termination of the stimulus suggested the activity of a metabolically driven process for the uptake of extracellular potassium.