Chronic ethanol exposure increases the association of hippocampal mu-opioid receptors with G-protein receptor kinase 2

Opioid receptors (ORs) have been shown to have a significant role in the central nervous system (CNS) effects of chronic ethanol consumption. The OR antagonist, naltrexone, is used clinically to reduce continued intake. We previously observed that chronic ethanol consumption, by adult male Sprague-Dawley rats, induced a reduction in functional coupling of mu- and delta-ORs to G-proteins in rat CNS regions, including the hippocampus. G-protein receptor kinase (GRK) 2 phosphorylates G-protein coupled receptors, including ORs, after agonist binding, as part of normal regulation and desensitization. We tested the hypothesis that chronic ethanol exposure affects the association of the GRK2 with the mu-OR. Co-immunoprecipitation methods were used to determine if mu-OR association with GRK2 is elevated in the hippocampus after chronic ethanol, when compared to controls. Hippocampal homogenates from chronic ethanol and pair-fed control rats were treated with affinity-purified rabbit polyclonal antibodies (ab) to mu-OR, and immune complexes were probed for GRK2 by immunoblotting techniques. Results demonstrate an association of GRK2 with mu-ORs in chronic ethanol-treated rats, but not in the controls. Possible changes in GRK2 association with ORs after chronic ethanol may be related to levels of phosphorylation and subsequent trafficking of the receptors. (C) 2008 Elsevier Inc. All rights reserved.