| First Author | Absalom N | Year | 2012 |
| Journal | Proc Natl Acad Sci U S A | Volume | 109 |
| Issue | 33 | Pages | 13404-9 |
| PubMed ID | 22753476 | Mgi Jnum | J:188413 |
| Mgi Id | MGI:5440525 | Doi | 10.1073/pnas.1204376109 |
| Citation | Absalom N, et al. (2012) alpha4betadelta GABA(A) receptors are high-affinity targets for gamma-hydroxybutyric acid (GHB). Proc Natl Acad Sci U S A 109(33):13404-9 |
| abstractText | 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 GABA(A) receptor subunits as possible candidates. A subsequent functional screening of various recombinant GABA(A) receptors in Xenopus laevis oocytes using the two-electrode voltage clamp technique showed GHB to be a partial agonist at alphabetadelta- but not alphabetagamma-receptors, proving that the delta-subunit is essential for potency and efficacy. GHB showed preference for alpha4 over alpha(1,2,6)-subunits and preferably activated alpha4beta1delta (EC(50) = 140 nM) over alpha4beta(2/3)delta (EC(50) = 8.41/1.03 mM). Introduction of a mutation, alpha4F71L, in alpha4beta1(delta)-receptors completely abolished GHB but not GABA function, indicating nonidentical binding sites. Radioligand binding studies using the specific GHB radioligand [(3)H](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 alpha4 KO brain tissue compared with WT controls, corroborating the direct involvement of the alpha4-subunit in high-affinity GHB binding. Our data link specific GHB forebrain binding sites with alpha4-containing GABA(A) receptors and postulate a role for extrasynaptic alpha4delta-containing GABA(A) 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. |
