Low concentrations of ethanol do not affect radioligand binding to the δ-subunit-containing GABA A receptors in the rat brain

Abstract

In the present study, we investigated the co-localization pattern of the δ subunit with other subunits of GABA A receptors in the rat brain using immunoprecipitation and Western blotting techniques. Furthermore, we investigated whether low concentrations of ethanol affect the δ-subunit-containing GABA A receptor assemblies in the rat brain using radioligand binding to the rat brain membrane homogenates as well as to the immunoprecipitated receptor assemblies. Our results revealed that δ subunit is not co-localized with γ 2 subunit but it is associated with the α 1, α 4 or α 6, β 2 and/or β 3 subunit(s) of GABA A receptors in the rat brain. Ethanol (1–50 mM) neither affected [ 3H]muscimol (3 nM) binding nor diazepam-insensitive [ 3H]Ro 15-4513 (2 nM) binding in the rat cerebellum and cerebral cortex membranes. However, a higher concentration of ethanol (500 mM) inhibited the binding of these radioligands to the GABA A receptors partially in the rat cerebellum and cerebral cortex. Similarly, ethanol (up to 50 mM) did not affect [ 3H]muscimol (15 nM) binding to the immunoprecipitated δ-subunit-containing GABA A receptor assemblies in the rat cerebellum and hippocampus but it inhibited the binding partially at a higher concentration (500 mM). These results suggest that the native δ-subunit-containing GABA A receptors do not play a major role in the pharmacology of clinically relevant low concentrations of ethanol.