GABA antagonists differentiate between recombinant GABAA/benzodiazepine receptor subtypes.
Seventeen rat GABAA receptor subtypes were transiently expressed in the human embryonic kidney 293 cell line from alpha 1, alpha 2, alpha 3, alpha 5, or alpha 6 variants with any of the three beta subunits and gamma 2S or gamma 3. We obtained fingerprints in the form of subtype characteristic concentration-response curves of 35S-TBPS binding to GABA and the GABAA antagonists SR 95531 and bicuculline. alpha 3 beta 3 gamma 2S/3 and alpha 5 beta 3 gamma 2S/3 containing receptors effectively recognized 35S-TBPS but not when beta 3 was replaced by the beta 1 or beta 2 subunit. This indicates a specific interaction of alpha and beta variants to form high-affinity 35S-TBPS binding sites. At low levels GABA allosterically increased 35S-TBPS binding to all receptors with the concentration and magnitude depending on the subunit combination. Exchange of the beta variant did not alter the concentration-response curves for alpha 1 and alpha 6 containing receptors but did so for alpha 2 containing receptors. alpha 2 beta 3 gamma 3 receptors displayed strong GABA-induced stimulation of 35S-TBPS binding, whereas binding to alpha 2 beta 3 gamma 3 receptors was marginally increased. SR 95531 and bicuculline decreased 35S-TBPS binding to all gamma 3 containing receptors. In addition, bicuculline was effective on alpha 1 beta x gamma 2 receptors. SR 95531 was threefold more potent than bicuculline in reversing GABA-induced modulation of 35S-TBPS binding in most receptor types, but was 30-fold more potent on alpha 2 beta 1 gamma 3 and alpha 6 beta 1 gamma 2S receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D001640:Bicuculline / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism; D002460:Cell Line; D004622:Embryo, Mammalian / Q000166:cytology; D018756:GABA Antagonists / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D007668:Kidney / Q000196:embryology; D011724:Pyridazines / Q000378:metabolism; D051381:Rats; D011963:Receptors, GABA-A / Q000187:drug effects*; D011995:Recombination, Genetic; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D019086:Bridged Bicyclo Compounds, Heterocyclic; D018756:GABA Antagonists; D011724:Pyridazines; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; C037476:tert-butylbicyclophosphorothionate; C049853:gabazine; D001640:Bicuculline