Low-dose alcohol actions on alpha4beta3delta GABAA receptors are reversed by the behavioral alcohol antagonist Ro15-4513.
Although it is now more than two decades since it was first reported that the imidazobenzodiazepine Ro15-4513 reverses behavioral alcohol effects, the molecular target(s) of Ro15-4513 and the mechanism of alcohol antagonism remain elusive. Here, we show that Ro15-4513 blocks the alcohol enhancement on recombinant "extrasynaptic" alpha4/6beta3delta GABA(A) receptors at doses that do not reduce the GABA-induced Cl(-) current. At low ethanol concentrations (< or =30 mM), the Ro15-4513 antagonism is complete. However, at higher ethanol concentrations (> or =100 mM), there is a Ro15-4513-insensitive ethanol enhancement that is abolished in receptors containing a point mutation in the second transmembrane region of the beta3 subunit (beta3N265M). Therefore, alpha4/6beta3delta GABA receptors have two distinct alcohol modulation sites: (i) a low-dose ethanol site present in alpha4/6beta3delta receptors that is antagonized by the behavioral alcohol antagonist Ro15-4513 and (ii) a site activated at high (anesthetic) alcohol doses, defined by mutations in membrane-spanning regions. Receptors composed of alpha4beta3N265Mdelta subunits that lack the high-dose alcohol site show a saturable ethanol dose-response curve with a half-maximal enhancement at 16 mM, close to the legal blood alcohol driving limit in most U.S. states (17.4 mM). Like in behavioral experiments, the alcohol antagonist effect of Ro15-4513 on recombinant alpha4beta3delta receptors is blocked by flumazenil and beta-carboline-ethyl ester (beta-CCE). Our findings suggest that ethanol/Ro15-4513-sensitive GABA(A) receptors are important mediators of behavioral alcohol effects.
Wallner
M
M
Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA 90095-1735, USA. mwallner@mednet.ucla.edu
Hanchar
H J
HJ
Olsen
R W
RW
D000818:Animals; D001386:Azides / Q000737:chemistry / Q000494:pharmacology*; D001569:Benzodiazepines / Q000737:chemistry / Q000494:pharmacology*; D002243:Carbolines / Q000737:chemistry; D004594:Electrophysiology; D004952:Esters / Q000737:chemistry / Q000494:pharmacology; D000431:Ethanol / Q000494:pharmacology*; D005442:Flumazenil / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists; D015394:Molecular Structure; D009154:Mutation / Q000235:genetics; D009865:Oocytes / Q000187:drug effects* / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D021122:Protein Subunits / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D001386:Azides; D002243:Carbolines; D004952:Esters; D058787:GABA-A Receptor Antagonists; D021122:Protein Subunits; D011963:Receptors, GABA-A; D001569:Benzodiazepines; D000431:Ethanol; D005442:Flumazenil; D005680:gamma-Aminobutyric Acid; C042957:Ro 15-4513