PT  - JOURNAL ARTICLE
AU  - Pratap Meera
AU  - Richard W. Olsen
AU  - Thomas S. Otis
AU  - Martin Wallner
TI  - Alcohol- and Alcohol Antagonist-Sensitive Human GABA<sub>A</sub> Receptors: Tracking δ Subunit Incorporation into Functional Receptors
AID  - 10.1124/mol.109.062687
DP  - 2010 Nov 01
TA  - Molecular Pharmacology
PG  - 918--924
VI  - 78
IP  - 5
4099  - http://molpharm.aspetjournals.org/content/78/5/918.short
4100  - http://molpharm.aspetjournals.org/content/78/5/918.full
SO  - Mol Pharmacol2010 Nov 01; 78
AB  - GABAA receptors (GABAARs) have long been a focus as targets for alcohol actions. Recent work suggests that tonic GABAergic inhibition mediated by extrasynaptic δ subunit-containing GABAARs is uniquely sensitive to ethanol and enhanced at concentrations relevant for human alcohol consumption. Ethanol enhancement of recombinant α4β3δ receptors is blocked by the behavioral alcohol antagonist 8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester (Ro15-4513), suggesting that EtOH/Ro15-4513-sensitive receptors mediate important behavioral alcohol actions. Here we confirm alcohol/alcohol antagonist sensitivity of α4β3δ receptors using human clones expressed in a human cell line and test the hypothesis that discrepant findings concerning the high alcohol sensitivity of these receptors are due to difficulties incorporating δ subunits into functional receptors. To track δ subunit incorporation, we used a functional tag, a single amino acid change (H68A) in a benzodiazepine binding residue in which a histidine in the δ subunit is replaced by an alanine residue found at the homologous position in γ subunits. We demonstrate that the δH68A substitution confers diazepam sensitivity to otherwise diazepam-insensitive α4β3δ receptors. The extent of enhancement of α4β3δH68A receptors by 1 μM diazepam, 30 mM EtOH, and 1 μM β-carboline-3-carboxy ethyl ester (but not 1 μM Zn2+ block) is correlated in individual recordings, suggesting that δ subunit incorporation into recombinant GABAARs varies from cell to cell and that this variation accounts for the variable pharmacological profile. These data are consistent with the notion that δ subunit-incorporation is often incomplete in recombinant systems yet is necessary for high ethanol sensitivity, one of the features of native δ subunit-containing GABAARs.