Factors affecting the spontaneous release of (3H)glycine from rabbit retina

The efflux of [3H]glycine was studied in superfused rabbit retina in the presence of various amino acids, ouabain, or high K+ or low Ca2+ concentrations in the superfusion medium. Unlabelled glycine evoked an accelerated efflux as did the structurally similar neutral alpha-amino acids. beta-alanine and GABA were ineffective. The results demonstrate a homoexchange of glycine, and a heteroexchange with the neutral alpha-amino acids. A low concentration of glutamic acid (10(-5) M) will release glycine from the retina. This is an ATPase dependent process which is partially blocked by a high Mg2+/Ca2+ ratio and which may be related to a retinal transmitter function of glutamic acid. A high concentration of K+ or the presence of ouabain in the superfusing medium greatly increases the rate at which glycine is lost from the retina.