期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2012
卷号：109
期号：33
页码：13404-13409
DOI：10.1073/pnas.1204376109
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：{gamma}-Hydroxybutyric acid (GHB) binding to brain-specific high-affinity sites is well-established and proposed to explain both physiological and pharmacological actions. However, the mechanistic links between these lines of data are unknown. To identify molecular targets for specific GHB high-affinity binding, we undertook photolinking studies combined with proteomic analyses and identified several GABAA receptor subunits as possible candidates. A subsequent functional screening of various recombinant GABAA receptors in Xenopus laevis oocytes using the two-electrode voltage clamp technique showed GHB to be a partial agonist at {beta}{delta}- but not {beta}{gamma}-receptors, proving that the {delta}-subunit is essential for potency and efficacy. GHB showed preference for 4 over (1,2,6)-subunits and preferably activated 4{beta}1{delta} (EC50 = 140 nM) over 4{beta}(2/3){delta} (EC50 = 8.41/1.03 mM). Introduction of a mutation, 4F71L, in 4{beta}1({delta})-receptors completely abolished GHB but not GABA function, indicating nonidentical binding sites. Radioligand binding studies using the specific GHB radioligand [3H](E,RS)-(6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylidene)acetic acid showed a 39% reduction (P = 0.0056) in the number of binding sites in 4 KO brain tissue compared with WT controls, corroborating the direct involvement of the 4-subunit in high-affinity GHB binding. Our data link specific GHB forebrain binding sites with 4-containing GABAA receptors and postulate a role for extrasynaptic 4{delta}-containing GABAA receptors in GHB pharmacology and physiology. This finding will aid in elucidating the molecular mechanisms behind the proposed function of GHB as a neurotransmitter and its unique therapeutic effects in narcolepsy and alcoholism.
