Affinity of various benzodiazepine site ligands in mice with a point mutation in the GABAA receptor γ2 subunit (original) (raw)

2004, Biochemical Pharmacology

The benzodiazepine binding site of GABA A receptors is located at the interface of the a and g subunits. Certain point mutations in these subunits have been demonstrated to dramatically reduce the affinity of benzodiazepine binding site ligands for these receptors. Recently, mice were generated with a phenylalanine (F) to isoleucine (I) substitution at position 77 in the g2 subunit of GABA A receptors. Here we tested the potency of 24 benzodiazepine binding site ligands from 16 different structural classes for inhibition of [ 3 H]flunitrazepam binding to brain membranes of these g2F77I mice. Results indicate that the potency of the classical 1,4-benzodiazepines, of the 1,4thienodiazepine clotiazepam, the 1,5-benzodiazepine clobazam, or the pyrazoloquinoline CGS 9896 is only 2-7-fold reduced by this g2F77I point mutation. The potency of the imidazopyrimidines Ru 32698, Ru 33203, and Ru 33356, of the imidazoquinoline Ru 31719, or the pyrazolopyridine CGS 20625 is reduced 10-20-fold, whereas the potency of some imidazobenzodiazepines, b-carbolines, cyclopyrrolones, imidazopyridines, triazolopyridazines, or quinolines is 100-1000-fold reduced. Interestingly, the extent of potency reduction induced by the g2F77I point mutation varied within the structural classes of compounds. Results support and significantly extend previous observations indicating that the residue g2F77 is important for high affinity binding of some, but not all benzodiazepine site ligands.