Desensitization of endogenously expressed delta-opioid receptors: no evidence for involvement of G protein-coupled receptor kinase 2

The involvement of G protein-coupled receptor kinase 2 (GRK2) in the agonis t-induced desensitization of delta -opioid receptor-mediated inhibition of cAMP formation in NG108-15 mouse neuroblastoma x rat glioma hybrid cells wa s investigated. Pretreatment of wild-type cells with the delta -opioid rece ptor agonist [D-Pen(2.5)]-enkephalin (DPDPE; 100 nM) for as little as 5 min produced marked desensitization of subsequent DPDPE-mediated inhibition of iloprost (300 nM)-stimulated cAMP formation. In NG108-15 cells stably over expressing wild-type GRK2 or dominant negative mutant GRK2 (DNM GRK2), the DPDPE-induced desensitization of cAMP inhibition was the same as in plasmid -transfected control cells. Pretreatment of wild-type cells with the inhibi tors of receptor internalization, concanavalin A (0.25 mg ml(-1)) or hypert onic sucrose (0.4 M), also failed. to inhibit DPDPE-mediated desensitizatio n. Finally, in NG108-15 cells stably overexpressing G protein-coupled recep tor kinase 6 (GRK6), DPDPE-induced desensitization was significantly increa sed as compared to plasmid-transfected control cells. These results indicat e that GRK2 is unlikely to mediate the desensitization of endogenous delta -opioid receptors in NG108-15 cells, but that other GRKs, such as GRK6, may be more important. (C) 2001 Elsevier Science B.V. All rights reserved.