Binding of the cage convulsant, [ 3H]TBOB, to sites linked to the GABA A receptor complex

Abstract

[ 3H]t-Butylbicycloorthobenzoate ([ 3H]TBOB) binds to specific sites on crude synaptic rat brain membranes. The dissociation constant, K d, determined from saturation experiments is near 8 nM and the receptor density B max is about 20 pmol/g wet tissue. Non-specific binding constitutes about 35% of the total binding at 4 nM [ 3H]TBOB. The association of [ 3H]TBOB is monophasic but its dissociation is biphasic. K d values of 8 nM (70% of the binding sites) and 20 nM (30% of the binding sites) were estimated from the kinetic data. These values differ from those previously reported. Specifically bound [ 3H]TBOB is displaced by picrotoxin and by t-butylbicyclophosphorothionate (TBPS). No simple competitive interaction of picrotoxin with [ 3H]TBOB binding was found. Micromolar quantities of the GABAergic facilitating compounds, GABA, muscimol and diazepam inhibited [ 3H]TBOB binding in an allosteric manner.