Light-evoked release of glycine from cat and rabbit retina

The light-evoked release of [3H]glycine from retina in cat (in vivo) after pre-retinal perfusion and in rabbit (in vitro) after intravitreal injection was studied. The site of uptake of [3H]glycine into retina was checked by autoradiography and was found to be almost exclusively in a type of amacrine cells. If the retina loaded with [3H]glycine was stimulated by light flashes the release increased significantly in both in vivo and in vitro experiments. When the flashing light was exchanged for continuous light there was not change in the spontaneous efflux of radioactivity. Chromatographic experiments showed that the main part of the radioactivity released by light was glycine. The light-evoked release of glycine from retina was dependent on temperature and Ca2+. Low temperature (+2 to +4 degrees C) abolished the increased release. If Ca2+ was ommitted from the perfusion medium and EDTA was added there was no light-inducable change in the efflux of radioactivity in retinas loaded with [3H]valine. The present results, that light stimulation will release glycine from the retina both in vivo and in vitro, are further criterion for it as neurotransmitter.