Contribution of the alpha1-GABA(A) receptor subtype to the pharmacological actions of benzodiazepine site inverse agonists.
A histidine-to-arginine point-mutation at position 101 in the alpha1-subunit of gamma-aminobutyric acid (GABA)(A) receptors has been shown to switch the in vitro efficacy of Ro 15-4513 from inverse agonism to agonism. In order to assess the consequences of this pharmacological switch in vivo, the motor and proconvulsant effects of Ro 15-4513 were analyzed in knock-in mice containing point-mutated alpha1(H101R)-GABA(A) receptors. Furthermore the influence of the alpha1(H101R) substitution on the efficacy of the beta-carboline inverse agonist DMCM was examined both in vitro and in vivo. Ro 15-4513 (10 mg/kg) increased baseline locomotion and potentiated the convulsant effect of pentylenetetrazole in wild type mice. In alpha1(H101R) mice, Ro 15-4513 decreased locomotion and, at a higher dose (30 mg/kg) it displayed an anticonvulsant action. In vitro, DMCM acted as an inverse agonist at recombinant alpha1beta2gamma2 receptors whereas it potentiated GABA-evoked chloride currents at alpha1(H101R)beta2gamma2 receptors. DMCM was inactive as a convulsant in alpha1(H101R) mice. In keeping with the major contribution of these receptors to the sedative and anticonvulsant properties of benzodiazepine site agonists, the present findings identify the alpha1-GABA(A) receptors as the molecular targets for the allosteric modulation by benzodiazepine site ligands in either direction with regard to the behavioral outputs, sedation/motor stimulation and anticonvulsion/proconvulsion.
D000818:Animals; D001386:Azides / Q000494:pharmacology; D001569:Benzodiazepines / Q000494:pharmacology; D002243:Carbolines / Q000494:pharmacology; D002460:Cell Line; D018118:Chloride Channels / Q000187:drug effects; D003292:Convulsants / Q000494:pharmacology; D004594:Electrophysiology; D018755:GABA Agonists / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D009043:Motor Activity / Q000187:drug effects; D010433:Pentylenetetrazole / Q000494:pharmacology; D017354:Point Mutation / Q000187:drug effects; D051381:Rats; D014162:Transfection; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D001386:Azides; D002243:Carbolines; D018118:Chloride Channels; D003292:Convulsants; D018755:GABA Agonists; D001569:Benzodiazepines; C034818:methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate; D005680:gamma-Aminobutyric Acid; C042957:Ro 15-4513; D010433:Pentylenetetrazole