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Pharmacology of the human gamma-aminobutyric acidA receptor alpha 4 subunit expressed in Xenopus laevis oocytes.
Mol Pharmacol. 1996 Nov; 50(5):1364-75.MP

Abstract

The human gamma-aminobutyric acidA (GABAA) receptor alpha 4 subunit was recently cloned and characterized pharmacologically using radioligand binding techniques. These studies suggested that alpha 4 subunits confer a novel diazepam-insensitive binding site. To further investigate the pharmacology of the alpha 4 subunit, we expressed human alpha 4 beta 2 gamma 2L subunit combinations in oocytes and compared the expression and pharmacology of these receptors with alpha 1 beta 2 gamma 2L, beta 2 gamma 2L, and other possible binary subunit combinations. Apparent GABA affinity was 2-3-fold higher for alpha 4 beta 2 gamma 2L than for alpha 1 beta 2 gamma 2L receptors. Functional modulation of receptors by benzodiazepine-site ligands and other classes of allosteric modulator were assayed over a broad concentration range (0.01-100 microM) on currents that were 10% of the maximum GABA response. Diazepam (0.01-1 microM) did not modulate GABA responses at alpha 4 beta 2 gamma 2L receptors, whereas it increased alpha 1 beta 2 gamma 2L responses by approximately 110%. Bretazenil (0.01-1 microM), a benzodiazepine partial agonist, induced higher efficacy modulation of alpha 4 beta 2 gamma 2L receptors (approximately 83%) than of alpha 1 beta 2 gamma 2L (approximately 25%). The benzodiazepine antagonist flumazenil (0.1-10 microM) unexpectedly potentiated alpha 4 beta 2 gamma 2L responses up to approximately 41%, and the benzodiazepine partial inverse agonist Ro15-4513 (1 microM) potentiated alpha 4 beta 2 gamma 2L responses by approximately 63%. Two other benzodiazepine-site ligands, CGS-9895 and methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, had qualitatively similar effects at alpha 1 beta 2 gamma 2L and alpha 4 beta 2 gamma 2L. Modulators such as pentobarbital, 3 alpha-hydroxy-5 alpha-pregnan-20-one, mefenamic acid, and loreclezole also induced similar potentiation at both subtypes of receptor. The pharmacology conferred by the alpha 4 subunit was similar to that conferred by the alpha 6 subunit, to which it shows highest levels of homology, but the two subunits differ in sensitivity to the beta-carboline methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate. Properties of the alpha 4-containing receptors are consistent with diazepam-insensitive binding sites found in cerebral cortex and other forebrain structures. Characterization of these receptors should further our understanding of mechanisms underlying the behavioral effects of GABA modulators and help in the design of drugs with improved, or novel, therapeutic profiles.

Authors+Show Affiliations

CoCensys, Inc., Irvine, California 92618, USA.No affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

8913369

Citation

Whittemore, E R., et al. "Pharmacology of the Human Gamma-aminobutyric acidA Receptor Alpha 4 Subunit Expressed in Xenopus Laevis Oocytes." Molecular Pharmacology, vol. 50, no. 5, 1996, pp. 1364-75.
Whittemore ER, Yang W, Drewe JA, et al. Pharmacology of the human gamma-aminobutyric acidA receptor alpha 4 subunit expressed in Xenopus laevis oocytes. Mol Pharmacol. 1996;50(5):1364-75.
Whittemore, E. R., Yang, W., Drewe, J. A., & Woodward, R. M. (1996). Pharmacology of the human gamma-aminobutyric acidA receptor alpha 4 subunit expressed in Xenopus laevis oocytes. Molecular Pharmacology, 50(5), 1364-75.
Whittemore ER, et al. Pharmacology of the Human Gamma-aminobutyric acidA Receptor Alpha 4 Subunit Expressed in Xenopus Laevis Oocytes. Mol Pharmacol. 1996;50(5):1364-75. PubMed PMID: 8913369.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Pharmacology of the human gamma-aminobutyric acidA receptor alpha 4 subunit expressed in Xenopus laevis oocytes. AU - Whittemore,E R, AU - Yang,W, AU - Drewe,J A, AU - Woodward,R M, PY - 1996/11/1/pubmed PY - 1996/11/1/medline PY - 1996/11/1/entrez SP - 1364 EP - 75 JF - Molecular pharmacology JO - Mol Pharmacol VL - 50 IS - 5 N2 - The human gamma-aminobutyric acidA (GABAA) receptor alpha 4 subunit was recently cloned and characterized pharmacologically using radioligand binding techniques. These studies suggested that alpha 4 subunits confer a novel diazepam-insensitive binding site. To further investigate the pharmacology of the alpha 4 subunit, we expressed human alpha 4 beta 2 gamma 2L subunit combinations in oocytes and compared the expression and pharmacology of these receptors with alpha 1 beta 2 gamma 2L, beta 2 gamma 2L, and other possible binary subunit combinations. Apparent GABA affinity was 2-3-fold higher for alpha 4 beta 2 gamma 2L than for alpha 1 beta 2 gamma 2L receptors. Functional modulation of receptors by benzodiazepine-site ligands and other classes of allosteric modulator were assayed over a broad concentration range (0.01-100 microM) on currents that were 10% of the maximum GABA response. Diazepam (0.01-1 microM) did not modulate GABA responses at alpha 4 beta 2 gamma 2L receptors, whereas it increased alpha 1 beta 2 gamma 2L responses by approximately 110%. Bretazenil (0.01-1 microM), a benzodiazepine partial agonist, induced higher efficacy modulation of alpha 4 beta 2 gamma 2L receptors (approximately 83%) than of alpha 1 beta 2 gamma 2L (approximately 25%). The benzodiazepine antagonist flumazenil (0.1-10 microM) unexpectedly potentiated alpha 4 beta 2 gamma 2L responses up to approximately 41%, and the benzodiazepine partial inverse agonist Ro15-4513 (1 microM) potentiated alpha 4 beta 2 gamma 2L responses by approximately 63%. Two other benzodiazepine-site ligands, CGS-9895 and methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, had qualitatively similar effects at alpha 1 beta 2 gamma 2L and alpha 4 beta 2 gamma 2L. Modulators such as pentobarbital, 3 alpha-hydroxy-5 alpha-pregnan-20-one, mefenamic acid, and loreclezole also induced similar potentiation at both subtypes of receptor. The pharmacology conferred by the alpha 4 subunit was similar to that conferred by the alpha 6 subunit, to which it shows highest levels of homology, but the two subunits differ in sensitivity to the beta-carboline methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate. Properties of the alpha 4-containing receptors are consistent with diazepam-insensitive binding sites found in cerebral cortex and other forebrain structures. Characterization of these receptors should further our understanding of mechanisms underlying the behavioral effects of GABA modulators and help in the design of drugs with improved, or novel, therapeutic profiles. SN - 0026-895X UR - https://www.unboundmedicine.com/medline/citation/8913369/Pharmacology_of_the_human_gamma_aminobutyric_acidA_receptor_alpha_4_subunit_expressed_in_Xenopus_laevis_oocytes_ L2 - http://molpharm.aspetjournals.org/cgi/pmidlookup?view=long&pmid=8913369 DB - PRIME DP - Unbound Medicine ER -