Study of the Mechanism of Release of [3H]GABA from a Teleost Retina In Vitro |
| |
Authors: | E. H. Jaffé ,N. Herná ndez,L. G. Holder |
| |
Affiliation: | Laboratorio de Neuroquimica, Centra de Biofisica y Bioquimica, Instituto Venezolano de Investigaciones Cientificas (IVIC), Caracas, Venezuela |
| |
Abstract: | Abstract: γ-Aminobutyric acid (GABA) is thought to be a neurotransmitter in the vetebrate retina. We studied the voltage and Ca2+ dependency of the process of release of [3H]GABA from the retina of the teleost Eugenes plumieri, using a microsuperfusion technique. Two depolarizing agents, veratridine and high potassium, produced a concentration-dependent release of [3H]GABA. The veratridine effect was inhibited in Na+-free solution, but was not affected by 1 μM tetrodotoxin. A substantial inhibition (about 75%) of the veratridine-and potassium-stimulated release of [3H] GABA occurred in Ca2+-free medium. Inhibitors of the Ca2+ channel, such as Mg2+(20 mM), La3+ (0.1 mM), and methoxy-verapamil (4 μM-0.4 mM), inhibited the veratridine-and K+-stimulated release. However, Co2+ and Cd2+ caused a potentiation and no change of the K+-and veratridine-stimulated release, respectively. This release process is apparently specific, since both depolarizing agents were unable to release [3H]methionine, a nontransmitter amino acid, under the same experimental conditions. Autoradio-graphic studies with [3H]GABA, using the same incubation conditions as for the release experiments, showed a high density of silver grains over the horizontal cells with almost no accumulation by amacrine cells and Muller cells. β-Alanine and nipecotic acid were used as two relative specific inhibitors of the glial and neuronal GABA uptake mechanisms, respectively. Only a small heteroexchange with [3H]GABA was found with β-alanine, and no inhibition of the subsequent veratridine-stimulated release. On the other hand, nipecotic acid produced a strong heteroexchange with [3H]GABA and lacked the capacity to induce the veratridine-stimulated release of [3H]GABA. These results suggest a voltage-and Ca2+-dependent neuronal release of [3H]GABA from retina. |
| |
Keywords: | γ-Aminobutyric acid Veratridine Calcium and voltage dependency Teleost retina |
|
|