CLONING OF CDNAS ENCODING THE HUMAN GAMMA-AMINOBUTYRIC-ACID TYPE-A RECEPTOR ALPHA-6 SUBUNIT AND CHARACTERIZATION OF THE PHARMACOLOGY OF ALPHA-6-CONTAINING RECEPTORS

A cDNA encoding the human gamma-aminobutyric acid(A) (GABA(A)) recepto r alpha 6 subunit has been cloned and sequenced. The deduced amino aci d sequence of this cDNA shows 91.4% identity with the published rat al pha 6 subunit. In situ hybridization histochemistry reveals the alpha 6 mRNA to be located within the granule cell layer of the human cerebe llar cortex. Recombinant human alpha 6 beta gamma 2S GABA(A) receptors have been expressed in both stably transfected cells and Xenopus oocy tes, and the pharmacology of the benzodiazepine binding site has been determined. The recombinant receptor has a diazepam-insensitive pharma cology, with negligible affinity for a number of classic benzodiazepin es. A number of compounds that bind to the benzodiazepine site potenti ated the GABA response of alpha 6 beta 2 gamma 2 receptors. Most impor tantly, the classic benzodiazepine antagonist 4H-imidazo[1,5-a][1,4]be nzodiazepine-3-carboxylate (Ro 15-1788) and the partial inverse agonis t 4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate (Ro 15-4513) both acted as agonists at the alpha 6 containing receptor. This observatio n demonstrates definitively that efficacy of benzodiazepine compounds cannot be generalized across receptor subtypes and may also help expla in some of the behavioral effects that have been reported for these co mpounds.