Depolarization-induced release of L-glutamic acid from isolated-resealed synaptic membrane vesicles

L-Glutamic acid actively loaded into resealed brain synaptic membrane vesicles was rapidly released into the incubation medium following the introduction of KCl and CaCl2, or nigericin, or veratridine into the external medium. The KCl-induced release was enhanced by the presence of low (0.1 mM), extravesicular [Ca2+]. Neither the KCl-induced nor the veratridine-stimulated L-glutamate efflux were carrier-mediated processes. Finally, the KCl-stimulated L-glutamate efflux was dependent on the ratio of intra- to extravesicular [K+]. The observations described in this study were indicative of depolarization-induced L-glutamate release from isolated synaptic plasma membrane vesicles.