Effect of Diethyl Pyrocarbonate Modification of Benzodiazepine Receptors on [3H]Ro 15-4513 Binding

The effects of treatment of brain membranes with diethyl pyrocarbonate (DEP), a histidine-modifying reagent, on the binding of 3H-labeled Ro 15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo1,5-a]- 1,4]benzodiazepine-3-carboxylate) and 3H]diazepam were compared. DEP pretreatment produced a dose-dependent decrease in 3H]diazepam binding, whereas low DEP concentrations enhanced the binding of 3H]Ro 15-4513. These effects were reversed by incubation with hydroxylamine after the treatment. The enhancement of 3H]Ro 15-4513 binding was due to an increase in the affinity of the binding sites (KD), without any effect on binding capacity (Bmax). The enhancement was perceived in cerebral cortical, cerebellar, and hippocampal membranes. DEP treatment decreased the displacement of 3H]Ro 15-4513 binding by diazepam and FG 7142 (N-methyl-beta-carboline-3-carboxamide) but not by Ro 15-4513 and Ro 19-4603 (tert-butyl-5,6-dihydro-5-methyl-6-oxo-4H-imidazol1,5- a]thieno2,3-f]1,4]diazepine-3-carboxylate). Although the stimulating effect of gamma-aminobutyric acid (GABA) on 3H]-diazepam binding was not affected by DEP treatment, such treatment reduced the inhibitory effect of GABA on 3H]Ro 15-4513 binding. The enhancement of 3H]Ro 15-4513 binding was observed in membranes pretreated with DEP in the presence of flunitrazepam, whereas such pretreatment reduced significantly the inhibitory effect of DEP on 3H]-diazepam binding.(ABSTRACT TRUNCATED AT 250 WORDS)