GABA induces down-regulation of the benzodiazepine-GABA receptor complex in the rat cultured neurons

Abstract

Cultured neurons from embryonic rat brain display central type benzodiazepine receptors characterized by high-affinity binding of [ 3H]flunitrazepam which is allosterically enhanced in the presence of γ-aminobutyric acid (GABA). A 48 h treatment of the cultured neurons with 1 μM diazepam, 0.1 μM clonazepam or 0.1 μM β-carboline ester derivatives did not change either B max or K D values of the [ 3H]flunitrazepam specific binding. A 48 h incubation in the presence of GABA (1 mM) or muscimol (0.1 mM) induced a 30% decrease of the B max value of [ 3H]flunitrazepam specific binding without change of the K D value. The down-regulation was dependent on GABA concentrations and temperature, and was partially inhibited by bicuculline but not by the benzodiazepine antagonist Ro 15–1788. The other subunits of the benzodiazepine-GABA-chloride channel receptor complex also seemed to be down-regulated by GABA since there was a decrease of the specific binding of [ 3H]muscimol and [ 35S]t-butylbicyclophosphorothionate (TBPS) to the GABA A and choride channel sites respectively. The GABA-induced down-regulation of the GABA-benzodiazepine receptor seems to be selective since the specific binding of ligands to other receptors was not affected. Our results suggests that activation of the low-affinity GABA subunit which is involved in cellular electrophysiological responses, induced the receptor down-regulation.