INTERACTIONS OF GAMMA-L-GLUTAMYLTAURINE WITH EXCITATORY AMINOACIDERGIC NEUROTRANSMISSION

The in vitro effects of gamma-L-glutamyltaurine on different stages of excitatory aminoacidergic neurotransmission were tested with gamma-D- glutamyltaurine as reference. gamma-L-Glutamyltaurine enhanced the K+- stimulated release of [H-3]glutamate from cerebral cortical slices (25 % at 0.1 mM) and slightly inhibited the uptake by crude brain synaptos omal preparations (about 10% at I mM). gamma-L-Glutamyltaurine was als o a weak displacer of glutamate and its agonists from their binding si tes in brain synaptic membrane preparations, being, however, less sele ctive to quisqualate (QA) sites than gamma-D-glutamyltaurine. The basa l influx of Ca2+ into cultured cerebellar granular cells was not affec ted by 1 mM gamma-L-glutamyltaurine, but the glutamate- and its agonis t-activated influx was significantly inhibited in low-Mg2+ (0.1 mM) an d Mg2+-free media. The glutamate-evoked increase in free intracellular Ca2+ and the kainate-activated formation of cGMP in cerebellar slices were both markedly inhibited by 0.1 mM gamma-L-glutamyltaurine. We pr opose that gamma-L-glutamyltaurine may act as endogenous modulator in excitatory aminoacidergic neurotransmission.