ALLOSTERIC MODULATION OF [H-3] FLUNITRAZEPAM BINDING TO RECOMBINANT GABA(A) RECEPTORS

The allosteric modulation of [H-3]flunitrazepam binding by gamma-aminobutyric acid (GABA), pentobarbital, (+)-etomidate, etazolate, alphaxalone, propofol and chlormethiazole was investigated in cerebellar membranes and membranes from human embryonic kidney (HEK) 293 cells transfected with alpha(1) beta(3) gamma(2) or alpha(1) gamma(2) subunits. Results obtained indicate that [H-3]flunitrazepam binding to recombinant GABA(A) receptors consisting of alpha(1) beta(3) gamma(2) 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 alpha(1) beta(3) gamma(2), but also those consisting of alpha(1) gamma(2) subunits exhibited [H-3]flunitrazepam binding which could be stimulated by GABA. In contrast to alpha(1) beta(3) gamma(2) receptors, however, [H-3]flunitrazepam binding to recombinant alpha(1) gamma(2) receptors was inhibited by pentobarbital, (+)-etomidate, etazolate, alphaxalone, propofol and chlormethiazole. This seems to indicate that binding sites for these compounds are present on alpha(1) gamma(2) receptors, but that their allosteric interaction with [H-3]flunitrazepam binding sites is different from that of alpha(1) beta(3) gamma(2) receptors.