Natural mutation of GABAA receptor alpha 6 subunit alters benzodiazepine affinity but not allosteric GABA effects.
The binding of the imidazobenzodiazepine, [3H]Ro 15-4513, to cerebellar granule cell-specific GABAA/benzodiazepine receptors is typically insensitive to benzodiazepine receptor agonists such as diazepam. A mutation in the alpha 6 subunit, causing replacement of the arginine at the 100 position by glutamine (Q100), has recently been found in an alcohol- and benzodiazepine-sensitive rat line. The mutant alpha 6(Q100)beta 2 gamma 2 recombinant receptors are sensitive to diazepam. The binding of [3H]Ro 15-4513 to cerebellar diazepam-insensitive receptors is enhanced by GABA, whereas binding to diazepam-sensitive receptors is inhibited. Recombinant receptors consisting of beta 2 and gamma 2 subunits together with the wildtype alpha 6 or mutant alpha 6(Q100) subunit showed positive modulation of [3H]Ro 15-4513 binding by GABA, whereas alpha 1 beta 2 gamma 2 receptors showed negative modulation. The picrotoxin-sensitive binding of a convulsant, t-butylbicyclophosphoro[35S]thionate ([35S]TBPS), was inhibited in the alpha 6 beta 2 gamma 2 and alpha 6(Q100) beta 2 gamma 2 receptors by GABA at concentrations less than one-tenth of those required in the alpha 1 beta 2 gamma 2 receptors. GABA effects on [35S]TBPS binding were only slightly affected by diazepam in the alpha 6(Q100) beta 2 gamma 2 receptors, while profound effects were seen in the alpha 1 beta 2 gamma 2 receptors in the presence of diazepam. The results with the mutant receptor suggest that the alpha 1 and alpha 6 subunits are responsible for differential allosteric actions by GABA on other binding sites, independently of the structures defining the benzodiazepine binding pharmacology.
Korpi
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ER
Biomedical Research Center, Alko Ltd., Helsinki, Finland.
Seeburg
P H
PH
D000818:Animals; D001386:Azides / Q000378:metabolism*; D001569:Benzodiazepines / Q000378:metabolism*; D001665:Binding Sites / Q000187:drug effects; D001643:Bridged Bicyclo Compounds / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002460:Cell Line; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism; D003001:Cloning, Molecular; D003292:Convulsants / Q000378:metabolism*; D003975:Diazepam / Q000494:pharmacology*; D006098:Granulocytes / Q000378:metabolism; D006801:Humans; D007668:Kidney / Q000166:cytology; D009118:Muscimol / Q000378:metabolism; D009154:Mutation; D010852:Picrotoxin / Q000494:pharmacology; D051381:Rats; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D001386:Azides; D001569:Benzodiazepines; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D003292:Convulsants; D003975:Diazepam; D009118:Muscimol; D010852:Picrotoxin; D011963:Receptors, GABA-A; D011994:Recombinant Proteins; D005680:gamma-Aminobutyric Acid; C037476:tert-butylbicyclophosphorothionate; C042957:Ro 15-4513