The release of Leu5-enkephalin-like immunoreactivity from chicken retina is reduced by light in vitro

A superfusion system was established to examine the efflux of endogenous Leu5-enkephalin-like immunoreactivity (LE-LI) from isolated chicken retinas. Superfusion with buffer containing high concentration of K+ (60 mM KCl) increased the efflux of LE-LI by 96%. This effect was not observed when Co2+ (4 mM CoCl2) was present. Exposing the retinas to light decreased the efflux of LE-LI by 59% compared to that observed during superfusion in the dark. No effect of ambient light could be detected in the presence of Co2+. Upon reverse-phase high-performance liquid chromatography the material released by the retina comigrated with synthetic Leu5-enkephalin. These results demonstrate that the release of LE-LI from retinal neurons is increased during the dark, and it is concluded that the lighting conditions exert their effects by modifying the state of polarization of the LE-LI amacrine cells and hence the release of LE-LI from these neurons.