title: 6,3'-Dinitroflavone is a low efficacy modulator of GABA(A) receptors.
abstract: 6,3'-Dinitroflavone (6,3'-DNF) is a synthetic flavone derivative that exerts anxiolytic effects in the elevated plus maze. Based on the finding that this effect is blocked by Ro15-1788 (ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate) which is a specific antagonist at the benzodiazepine binding site of GABA(A) receptors we investigated the interaction of 6,3'-DNF with several recombinant GABA(A) receptor subtypes. Inhibition of [(3)H]flunitrazepam binding to recombinant GABA(A) receptors in transiently transfected HEK293 cells indicated that 6,3'-DNF exhibited the highest affinity for GABA(A) receptors composed of alpha1beta2gamma2 subunits and a 2-20 fold lower affinity for homologous receptors containing alpha2, alpha3, or alpha5 subunits. Two-electrode voltage-clamp experiments in Xenopus oocytes indicated that 6,3'-DNF does not induce chloride flux in the absence of GABA, but exerts low efficacy inverse agonistic modulatory effects on GABA-elicited currents in the GABA(A) receptor subtypes alpha1beta2gamma2 and alpha5beta2gamma2. In the subtypes alpha2beta2gamma2, alpha3beta2gamma2, alpha4beta2gamma2, alpha6beta2gamma2 or alpha4beta2delta and alpha4beta3delta, 6,3'-DNF exerts either none or very low efficacy positive modulatory effects. In contrast, 100 nM Ro15-1788 exhibited weak to moderate partial agonistic effects on each receptor investigated. These data indicate that Ro15-1788 only can antagonize the weak inverse agonist effects of 6,3'-DNF on alpha1beta2gamma2 and alpha5beta2gamma2 receptors, but will enhance the weak agonistic effects on the other receptor subtypes investigated. The possible mechanism of the Ro15-1788 sensitive anxiolytic effect of 6,3'-DNF is discussed.
authors.affiliation: Center for Brain Research, Medical University of Vienna, A-1090 Vienna, Austria.
authors.forename: Roman
authors.initials: R
authors.lastname: Furtmueller
authors.forename: Birgit
authors.initials: B
authors.lastname: Furtmueller
authors.forename: Joachim
authors.initials: J
authors.lastname: Ramerstorfer
authors.forename: Alejandro C
authors.initials: AC
authors.lastname: Paladini
authors.forename: Cristina
authors.initials: C
authors.lastname: Wasowski
authors.forename: Mariel
authors.initials: M
authors.lastname: Marder
authors.forename: Sigismund
authors.initials: S
authors.lastname: Huck
authors.forename: Werner
authors.initials: W
authors.lastname: Sieghart
mesh_terms: D000818:Animals; D014151:Anti-Anxiety Agents / Q000378:metabolism*; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism; D005260:Female; D005419:Flavonoids / Q000378:metabolism*; D005442:Flumazenil / Q000494:pharmacology*; D005445:Flunitrazepam / Q000378:metabolism; D018757:GABA Modulators / Q000494:pharmacology; D006801:Humans; D009865:Oocytes; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D021122:Protein Subunits / Q000378:metabolism; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000378:metabolism; D014162:Transfection; D014981:Xenopus
chemical_list: D014151:Anti-Anxiety Agents; D002712:Chlorides; D005419:Flavonoids; D018757:GABA Modulators; D021122:Protein Subunits; D011963:Receptors, GABA-A; C105566:3',6-dinitroflavone; D005442:Flumazenil; D005445:Flunitrazepam