Laminar separation of light-evoked K+ flux and field potentials in frog retina.

Light-evoked changes in [K+] 0 and field potentials were recorded from the retinas of grass frogs. In the proximal retina, light induced an increase in [K+]0. This increase had components at light onset and offset, was maximal with small spot stimulation, and reached greatest amplitude at the same depth as the proximal negative response (PNR). Extracellular dye marking revealed that this depth was within the inner plexiform layer. The off-components of both the K+ increase and PNR occurred distal to the on-components, thus supporting recent proposal that "off" synapases lie distal to "on" synapses. Since a well-developed M-wave, having a time course nearly identical to the K+ increase, was also seen in the proximal retina, this field potential appears to be a normal component of the intraretinal electroretinogram.