Specific stimulating effect of glycine on 3H-dopamine efflux from substantia nigra slices of the rat.

The effect of glycine was studied on the efflux of tritium-labelled dopamine, 5-HT and GABA from small slices of rat substantia nigra in vitro. A depolarising stimulus (50 mM KCl) stimulated the efflux of 3H-5HT, 3H-dopamine and 3H-GABA in a calcium-dependent fashion. Glycine (50 and 100 micromoles) stimulated the spontaneous efflux of 3H-dopamine but not that of 3H-5HT or 3H-GABA. Taurine, GABA and beta-alanine, all at 100 micromoles, had no effect on release of radioactivity after prelabelling nigral slices with 3H-dopamine. In keeping with a transmitter role for glycine at this site, 3H-glycine was taken up by small slices of rat substantia nigra by both high affinity (Km = 2.4 micromoles) and low affinity systems (Km = 5.96 mM). However 50 mM KCl was without effect on the efflux of radioactivity from nigral slices prelabelled with 3H-glycine.