GAMMA-AMINOBUTYRIC-ACID (A) RECEPTOR PHARMACOLOGY IN RAT CEREBRAL CORTICAL SYNAPTONEUROSOMES

Equilibrium binding interactions at the gamma-aminobutyric acid (GABA) and benzodiazepine recognition sites on the GABA(A) receptor-Cl- ionophore complex were studied using a vesicular synaptoneurosome (microsacs) preparation of rat brain in a physiological HEPES buffer similar to that applied successfully in recent GABAergic Cl-36(-) flux measurements. NO 328, a GABA reuptake inhibitor, was included in the binding assays to prevent the uptake of [H-3]muscimol. Under these conditions, the equilibrium dissociation constant (K(D)) values for [H-3]muscimol and [H-3]diazepam binding are 1.9-mu-M and 40 nM, respectively. Binding affinities for these and other GABA and benzodiazepine agonists and antagonists correlate well with the known physiological doses required to elicit functional activity. This new in vitro binding protocol coupled with Cl-36(-) flux studies should prove to be of value in reassessing the pharmacology of the GABA(A) receptor complex in a more physiological environment.