Interaction of allosteric ligands with GABAA receptors containing one, two, or three different subunits

The presence of allosteric binding sites on recombinant GABAA receptors formed after transfection of human embryonic kidney (HEK) 293 cells with α1-, β3-, γ2-subunits, or with various combinations of these subunits, was systematically investigated. From all possible subunit combinations, high affinity [3H]muscimol binding sites were induced in cells transfected with α1 β3- or α1 β3γ2-subunits only. GABAA receptor associated [3H]flunitrazepam binding sites were induced in cells after transfection with α1 γ2- or α1 β3γ2-subunits, and [35S]t-butylbicyclophosphorothionate (TBPS) binding sites were found in cells transfected with β3-, β3γ2-, α1 β3-, or α1 β3γ2-subunits. Binding of [35S]TBPS could be inhibited by pentobarbital, etazolate, (+)-etomidate, alphaxalone, propofol, chlormethiazole, and 4′-chlorodiazepam (Ro 5-4864) with a potency which differed in cells transfected with β3-, β3γ2-, α1 β3-, or α1 β3γ2-subunits. Results obtained indicate that receptors with different subunit composition actually can be formed in HEK cells and exhibit distinct pharmacological properties.