The point mutation γ2F77I changes the potency and efficacy of benzodiazepine site ligands in different GABAA receptor subtypes

Benzodiazepine site agonists or inverse agonists enhance or reduce γ-aminobutyric acidA (GABAA) receptor-mediated inhibition of neurons, respectively. Recently, it was demonstrated that the point mutation γ2F77I causes a drastic change in the affinity of a variety of benzodiazepine agonists or inverse agonists in receptor binding studies. Here we investigated the potency and efficacy of 10 benzodiazepine site ligands from 6 structural classes in wild-type and γ2F77I point mutated recombinant GABAA receptors composed of α1β3γ2, α2β3γ2, α3β3γ2, α4β3γ2, α5β3γ2, and α6β3γ2 subunits. Results indicate that the effects of the benzodiazepine site ligands zolpidem, zopiclone, Cl218872, L-655,708 and DMCM were nearly completely eliminated in all mutated receptors up to a 1 μM concentration. The effects of bretazenil, Ro15-1788 or abecarnil were eliminated in some, but not all mutated receptors, suggesting that the γ2F77I mutation differentially influences the actions of these ligands in different receptor subtypes. In addition, this point mutation also influences the efficacy of diazepam for enhancing GABA-induced chloride flux, suggesting that the amino acid residue γ2F77 might also be involved in the transduction of the effect of benzodiazepines from binding to gating. The application of these drugs in a novel mouse model is discussed.