Baur Roland, Kaur Kuldeep H, Sigel Erwin
Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland.
J Neurochem. 2009 Dec;111(5):1172-81. doi: 10.1111/j.1471-4159.2009.06387.x. Epub 2009 Sep 18.
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.
含δ亚基的GABA(A)受体在突触外表达并介导紧张性抑制。在小脑颗粒细胞中，它们常与α(6)亚基共同形成一种受体。我们有兴趣确定这些受体的结构。我们通过亚基连接预先定义了24种不同GABA(A)受体五聚体的亚基排列。这些受体（由α(6)、β(3)和δ亚基组成）在非洲爪蟾卵母细胞中表达，并分析其电生理特性。在存在和不存在3α,21-二羟基-5α-孕烷-20-酮以及4,5,6,7-四氢异恶唑并[5,4-c]-吡啶-3-醇的情况下，测定对GABA产生的电流。α(6)-β(3)-α(6)/δ受体对单独的GABA有显著反应。三种受体，β(3)-α(6)-δ/α(6)-β(3)、α(6)-β(3)-α(6)/β(3)-δ和β(3)-δ-β(3)/α(6)-β(3)，仅在神经甾体3α,21-二羟基-5α-孕烷-20-酮与GABA共同存在时才被发现。所有四种受体均被4,5,6,7-四氢异恶唑并[5,4-c]-吡啶-3-醇激活。没有一种功能性受体受到生理浓度（高达30 mM）乙醇的调节。GABA浓度反应曲线表明δ亚基可有助于激动剂位点的形成。从所研究的受体中我们得出结论，在由α(6)、β(3)和δ亚基组成的受体五聚体中，δ亚基可占据多个位置。
