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

In the present study, we investigated the co-localization pattern of the δ subunit with other subunits of GABAA receptors in the rat brain using immunoprecipitation and Western blotting techniques. Furthermore, we investigated whether low concentrations of ethanol affect the δ-subunit-containing GABAA 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 γ2 subunit but it is associated with the α1, α4 or α6, β2 and/or β3 subunit(s) of GABAA 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 GABAA 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 GABAA 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 GABAA receptors do not play a major role in the pharmacology of clinically relevant low concentrations of ethanol.