EFFECT OF GAMMA-VINYL GAMMA-AMINOBUTYRIC-ACID ON THE GAMMA-AMINOBUTYRIC-ACID RECEPTOR-COUPLED CHLORIDE-ION CHANNEL IN VESICLES FROM THE BRAIN OF THE RAT

The effect of gamma-vinyl GABA on the gamma-aminobutyric acid (GABA) receptor-coupled chloride ion (Cl-) channel was studied using membrane vesicles from cerebral cortex of the rat. gamma-Vinyl GABA, an antiepileptic drug, had no effect on uptake of Cl-36-, without preincubation. However, preincubation of membrane vesicles with gamma-vinyl GABA (100-1000-mu-M) produced a concentration-dependent decrease in net uptake of Cl-36-. No alteration was observed in basal uptake of Cl-36-. This decrease in net uptake of Cl-36- was not related to desensitization induced by endogenous GABA, which might be increased by gamma-vinyl GABA through selective, irreversible inhibition of GABA-transaminase (GABA-T). Concentration-response curves for GABA showed that preincubation with gamma-vinyl GABA inhibited GABA-stimulated uptake of Cl-36- with no change in ED50. These results indicate that gamma-vinyl GABA may act directly at the GABA/benzodiazepine ionophore complex, as a non-competitive antagonist of GABA.