Allosteric modulation of [3H]flunitrazepam binding to recombinant GABAA receptors

Abstract

The allosteric modulation of [³H]flunitrazepam binding by γ-aminobutyric acid (GABA), pentobarbital, (+)-etomidate, etazolate, alphaxalone, propofol and chlormethiazole was investigated in cerebellar membranes from human embryonic kidney (HEK) 293 cells transfected with α₁β₃γ₂ or α₁γ₂ subunits. Results obtained indicate that [³H]flunitrazepam binding to recombinant GABA_A receptors consisting of α₁β₃γ₂ subunits could be modulated by these compounds in a way and with a potency similar to that observed in cerebellar membranes. In addition, it was demonstrated that not only receptors consisting of α₁β₃γ₂, but also those consisting of α₁γ₂ subunits exhibited [³H]flunitrazepam binding which could be stimulated by GABA. In contrast to α₁β₃γ₂ receptors, however, [³H]flunitrazepam binding to recombinant α₁γ₂ receptors was inhibited by pentobarbital, (+)-etomidate, etazolate, alphaxalone, propofol and chlormethiazole. This seems to indicate that binding sites for these compounds are present on α₁γ₂ receptors, but that their allosteric interaction with [³H]flunitrazepam binding sites is different from that of α₁β₃γ₂ receptors.