title: Structure of alpha6 beta3 delta GABA(A) receptors and their lack of ethanol sensitivity.
abstract: Delta (delta) subunit containing GABA(A) receptors are expressed extra-synaptically and mediate tonic inhibition. In cerebellar granule cells, they often form a receptor together with alpha(6) subunits. We were interested to determine the architecture of these receptors. We predefined the subunit arrangement of 24 different GABA(A) receptor pentamers by subunit concatenation. These receptors (composed of alpha(6), beta(3) and delta subunits) were expressed in Xenopus oocytes and their electrophysiological properties analyzed. Currents elicited in response to GABA were determined in presence and absence of 3alpha, 21-dihydroxy-5alpha-pregnan-20-one and to 4,5,6,7-tetrahydroisoxazolo[5,4-c]-pyridin-3-ol. alpha(6)-beta(3)-alpha(6)/delta receptors showed a substantial response to GABA alone. Three receptors, beta(3)-alpha(6)-delta/alpha(6)-beta(3), alpha(6)-beta(3)-alpha(6)/beta(3)-delta and beta(3)-delta-beta(3)/alpha(6)-beta(3), were only uncovered in the combined presence of the neurosteroid 3alpha, 21-dihydroxy-5alpha-pregnan-20-one with GABA. All four receptors were activated by 4,5,6,7-tetrahydroisoxazolo[5,4-c]-pyridin-3-ol. None of the functional receptors was modulated by physiological concentrations (up to 30 mM) of ethanol. GABA concentration response curves indicated that the delta subunit can contribute to the formation of an agonist site. We conclude from the investigated receptors that the delta subunit can assume multiple positions in a receptor pentamer composed of alpha(6), beta(3) and delta subunits.
authors.affiliation: Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland.
authors.forename: Roland
authors.initials: R
authors.lastname: Baur
authors.forename: Kuldeep H
authors.initials: KH
authors.lastname: Kaur
authors.forename: Erwin
authors.initials: E
authors.lastname: Sigel
mesh_terms: D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology; D055592:Biophysical Phenomena / Q000187:drug effects* / Q000235:genetics; D002492:Central Nervous System Depressants / Q000494:pharmacology*; D003900:Desoxycorticosterone / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D000431:Ethanol / Q000494:pharmacology*; D018755:GABA Agonists / Q000494:pharmacology; D007555:Isoxazoles / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology; D009865:Oocytes; D018408:Patch-Clamp Techniques; D021122:Protein Subunits / Q000235:genetics / Q000502:physiology; D011963:Receptors, GABA-A / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D014162:Transfection / Q000379:methods; D014981:Xenopus; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D014151:Anti-Anxiety Agents; D002492:Central Nervous System Depressants; D018755:GABA Agonists; D007555:Isoxazoles; D021122:Protein Subunits; D011963:Receptors, GABA-A; D000431:Ethanol; D003900:Desoxycorticosterone; C009413:tetrahydrodeoxycorticosterone; D005680:gamma-Aminobutyric Acid; C015542:gaboxadol