Portal de Periódicos da CAPES

Effects of d-aspartate on excitatory amino acid-induced release of [3H]GABA from goldfish retina

1986; Elsevier BV; Volume: 376; Issue: 1 Linguagem: Inglês

10.1016/0006-8993(86)90908-x

1872-6240

J. Jang‐Ho, Denis R. O'Brien, John E. Dowling,

Biochemical effects in animals

The rate of release of [3H]GABA from isolated intact goldfish retinas was studied. Release of [3H]GABA is markedly stimulated by the inclusion in the incubation medium of the photoreceptor neurotransmitter candidates l-glutamate (l-Glu) and l-aspartate (l-Asp), and the glutamate analogs, kainate and quisqualate. At micromolar concentrations, kainate and quisqualate are effective releasers of [3H]GABA, whereas millimolar concentrations of l-Glu and l-Asp are required to release comparable amounts of [3H]GABA. The d-isomers of aspartate (d-Asp) and glutamate (d-Glu) are able to release [3H]GABA, but only when applied at high concentrations (3–30 mM). In the presence of 5 mM d-Asp, the effect of l-Glu in releasing [3H]GABA was markedly potentiated. This dose-response curve of l-Glu was shifted to the left in the presence of d-Asp, although the maximal amount of release was unchanged. d-Asp at 5 mM only slightly increased the GABA release induced by quisqualate, and it did not increase the GABA release induced by kainate. Finally, low concentrations of l-Asp were potentiated by d-Asp, but higher concentrations of l-Asp (3–10 mM) were clearly inhibited by this agent. This biphasic effect of d-Asp on l-Asp-induced release of [3H]GABA is a possible explanation for previously conflicting reports of d-Asp's effect on l-Asp action2,8,29. Our data suggest that d-Asp has both pre- and postsynaptic sites of action.