Light-evoked changes in extracellular potassium concentration in munpuppy retina.

Light-evoked changes in extracellular potassium concentration ([K+]0) and field potentials were recorded simultaneously in response to a wide variety of stimuli and at various depths within the retina of Necturus. At both light onset and offset, small diameter flashed stimuli elicit a large increase in [K+]0 in the proximal retina. The depth profile of this K+ increase is nearly identical to that of the proximal negative response (PNR), and both responses exhibit similar behavior to a number of other stimulus parameters. This suggests that the same neurons which generate the PNR may be the source of the observed K+ flux. Large diameter flashed stimuli elicit a slow decrease in [K+]0 in the distal retina and a small increase proximally. The K+ increase occurs at a depth where the b-wave of the electroretinogram is positive going, and where its current source lies. Increasing background light intensity decreases [K+]0 in the distal retina, and generally increases [K+]0 proximally.