Selective interactions of the rat μ-opioid receptor and a chimeric μ-opioid receptor expressed in COS-7 cells with multiple G proteins

Abstract

Agonist activation of all three opioid receptor subtypes μ, δ, and κ has been reported to result in the inhibition of adenylate cyclase and/or the regulation of ion channels by activation of one or more pertussis toxin sensitive guanine nucleotide binding proteins acting as signal transducers (1). cDNA species encoding each of the μ, δ and κ opioid receptors have been reported (2 and references therein). However, the question of which heterotrimeric G protein(s) is involved in a specific opioid function remains still unclear. Therefore expression of these species in heterologous systems would allow a more detail examination of the signalling characteristics of these receptors. In order to explore in detail the molecular identity of the pertussis toxin sensitive G proteins activated by the μ-opioid receptor, we transiently transfected a wild type cDNA corresponding to rat μ-opioid receptor and a chimeric μ-opioid receptor construct composed of the rat μ-opioid receptor and a N-terminal hydrophilic Flag epitope, into COS-7 cells. Moreover, co-transfection of a cDNA encoding G_oa was also accomplished. The purpose of the present study was to investigate the specific interactions between the expressed μ-opioid receptors with native G protein(s) or co-transfected G_oa.