title: γ-aminobutyric acid type A α4, β2, and δ subunits assemble to produce more than one functionally distinct receptor type.
abstract: Native γ-aminobutyric acid (GABA)A receptors consisting of α4, β1-3, and δ subunits mediate responses to the low, tonic concentration of GABA present in the extracellular milieu. Previous studies on heterologously expressed α4βδ receptors have shown a large degree of variability in functional properties, including sensitivity to the transmitter. We studied properties of α4β2δ receptors employing free subunits and concatemeric constructs, expressed in Xenopus oocytes, HEK 293 cells, and cultured hippocampal neurons. The expression system had a strong effect on the properties of receptors containing free subunits. The midpoint of GABA activation curve was 10 nM for receptors in oocytes versus 2300 nM in HEK cells. Receptors activated by the steroid alfaxalone had an estimated maximal open probability of 0.6 in oocytes and 0.01 in HEK cells. Irrespective of the expression system, receptors resulting from combining the tandem construct β2-δ and a free α4 subunit exhibited large steroid responses. We propose that free α4, β2, and δ subunits assemble in different configurations with distinct properties in oocytes and HEK cells, and that subunit linkage can overcome the expression system-dependent preferential assembly of free subunits. Hippocampal neurons transfected with α4 and the picrotoxin-resistant δ(T269Y) subunit showed large responses to alfaxalone in the presence of picrotoxin, suggesting that α4βδ receptors may assemble in a similar configuration in neurons and oocytes.
authors.affiliation: Department of Anesthesiology (M.M.E., J.B., P.L., J.H.S., G.A.), Department of Psychiatry (H.-J.S., S.M.), and Taylor Family Institute for Innovative Psychiatric Research (S.M., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Megan M
authors.initials: MM
authors.lastname: Eaton
authors.affiliation: Department of Anesthesiology (M.M.E., J.B., P.L., J.H.S., G.A.), Department of Psychiatry (H.-J.S., S.M.), and Taylor Family Institute for Innovative Psychiatric Research (S.M., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri.
authors.forename: John
authors.initials: J
authors.lastname: Bracamontes
authors.affiliation: Department of Anesthesiology (M.M.E., J.B., P.L., J.H.S., G.A.), Department of Psychiatry (H.-J.S., S.M.), and Taylor Family Institute for Innovative Psychiatric Research (S.M., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Hong-Jin
authors.initials: HJ
authors.lastname: Shu
authors.affiliation: Department of Anesthesiology (M.M.E., J.B., P.L., J.H.S., G.A.), Department of Psychiatry (H.-J.S., S.M.), and Taylor Family Institute for Innovative Psychiatric Research (S.M., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Ping
authors.initials: P
authors.lastname: Li
authors.affiliation: Department of Anesthesiology (M.M.E., J.B., P.L., J.H.S., G.A.), Department of Psychiatry (H.-J.S., S.M.), and Taylor Family Institute for Innovative Psychiatric Research (S.M., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Steven
authors.initials: S
authors.lastname: Mennerick
authors.affiliation: Department of Anesthesiology (M.M.E., J.B., P.L., J.H.S., G.A.), Department of Psychiatry (H.-J.S., S.M.), and Taylor Family Institute for Innovative Psychiatric Research (S.M., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Joe Henry
authors.initials: JH
authors.lastname: Steinbach
authors.affiliation: Department of Anesthesiology (M.M.E., J.B., P.L., J.H.S., G.A.), Department of Psychiatry (H.-J.S., S.M.), and Taylor Family Institute for Innovative Psychiatric Research (S.M., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri akk@morpheus.wustl.edu.
authors.forename: Gustav
authors.initials: G
authors.lastname: Akk
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D057809:HEK293 Cells; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology; D006801:Humans; D011277:Pregnanediones / Q000494:pharmacology; D021122:Protein Subunits; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000737:chemistry* / Q000187:drug effects / Q000502:physiology*; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D011277:Pregnanediones; D021122:Protein Subunits; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; C006477:alphaxalone