GROUP-SELECTIVE REAGENT MODIFICATION OF THE BENZODIAZEPINE-GAMMA-AMINOBUTYRIC ACID RECEPTOR-IONOPHORE COMPLEX REVEALS THAT LOW-AFFINITY GAMMA-AMINOBUTYRIC ACID RECEPTORS STIMULATE BENZODIAZEPINE BINDING

  • 1 January 1983
    • journal article
    • research article
    • Vol. 23  (1) , 52-59
Abstract
The modification of membrane proteins with diethylpyrocarbonate (DEP) and diazotized sulfanilate was investigated on the binding of 3 benzodiazepine radioligands in 3 [rat] brain regions. Both of these reagents produced a dose-dependent inactivation of [3H]diazepam, [3H]flunitrazepam and [3H]propyl .beta.-carboline-3-carboxylate binding to cortex, cerebellum and hippocampus. Both DEP and diazotized sulfanilate decrease the Bmax [maximum binding] of the benzodiazepine binding sites without altering the Kd. The ability of muscimol and pentobarbital to enhance [3H]diazepam binding was not altered by DEP pretreatment in any of the 3 regions. Scatchard analysis indicated that, following the inactivation of 40-50% of [3H]diazepam binding by 1 mM DEP, pentobarbital and muscimol were still able to increase the affinity of [3H]diazepam binding in cortex, cerebellum and hippocampus. Diazotized sulfanilate pretreatment abolishes the ability of muscimol and pentobarbital to enhance [3H]diazepam binding in these 3 regions. The effects of these reagents on [3H]GABA binding revealed that sulfanilate but not DEP eliminates the low-affinity GABA receptor sites in cortex and cerebellum. While both DEP and sulfanilate inactivate benzodiazepine binding sites, only sulfanilate abolishes the low-affinity GABA binding sites and the ability of the GABA agonists to enhance [3H]diazepam binding. The stimulation of benzodiazepine binding appears to be mediated by the low-affinity GABA receptors.