The effects of a competitive antagonist on GABA-evoked currents in the presence of sedative-hypnotic agents

Abstract

Background-Many sedative-hypnotic agents are thought to act by positively modulating γaminobutyric acid type A (GABA A ) receptors. However, for many agents, the location(s) of the binding site(s) responsible for such receptor modulation is uncertain. We previously developed a low efficacy ligand (naphthalene-etomidate) that binds within a homologous set of hydrophobic cavities located at GABA A receptor subunit interfaces in the transmembrane domain and thus acts as a competitive antagonist for higher efficacy sedative-hypnotics that also bind to these sites. In this report, we describe studies using this compound as a pharmacological screening tool to test whether sedative-hypnotics representing a range of chemical classes can modulate GABA A receptors by binding within these receptor cavities.Methods-The impact of naphthalene-etomidate on GABA-evoked currents that were mediated by oocyte-expressed α 1 β 3 γ 2L GABA A receptors and potentiated by muscimol, alphaxalone, 2,2,2trichloroethanol, isoflurane, AA29504, loreclezole, or diazepam was quantified using electrophysiological techniques.Results-Naphthalene-etomidate (300 μM) significantly reduced GABA A receptor currents potentiated by alphaxalone (by 22 ± 11%), 2,2,2-trichloroethanol (by 23 ± 6%), isoflurane (by 32 ± 10%), AA29504 (by 41 ± 6%), loreclezole (by 43 ± 9%), but significantly increased those potentiated by muscimol (by 26 ± 11%). Naphthalene-etomidate significantly increased currents potentiated by a low (1 μM) diazepam concentration (by 56 ± 14%) while reducing those potentiated by a high (100 μM) diazepam concentration (by 11 ± 7%).Terms of use and reuse: academic research for non-commercial purposes, see here for full terms. https://www.springer.com/aamterms-v1

The Influence of AA29504 on GABAA Receptor Ligand Binding Properties and Its Implications on Subtype Selectivity

“…AA29504 agonist behavior, nevertheless, was not dependent on the presence of γ2 and δ subunits and even displaced [ 3 H]EBOB with higher efficiency in α6β3 compared to α6β3δ and α6β3γ2 receptors. This further suggests the role of GABA A R’s transmembrane β + /α − interface in exerting AA29504 pharmacological activity [ 27 , 49 ], as similarly found for neurosteroids [ 50 , 51 ] and general anesthetics such as etomidate and propofol [ 52 , 53 ]. Functional assessment at numerous mutant GABA A Rs and on in silico analysis of its low-energy conformations indicated that AA29504 and etomidate exert their effects through the same site or overlapping binding sites between α-TM1 and β-TM3 transmembrane domains [ 27 ].…”