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Effects of C‐Terminal Truncation of the Recombinant δ‐Opioid Receptor on Phospholipase C and Adenylyl Cyclase Coupling
Author(s) -
Hirst Robert A.,
Smart Darren,
Devi Lakshmi A.,
Lambert David G.
Publication year - 1998
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1998.70062273.x
Subject(s) - adenylyl cyclase , g protein , receptor , pertussis toxin , second messenger system , phospholipase c , chinese hamster ovary cell , medicine , enkephalin , adenylate cyclase toxin , endocrinology , inositol phosphate , cyclase , chemistry , μ opioid receptor , biology , inositol , biochemistry , opioid
Opioid receptors belong to the superfamily of guanine nucleotide binding (G) protein‐coupled receptors. There is now growing evidence in support of a stimulatory coupling of opioid receptors to phospholipase C (PLC), via a pertussis toxin‐sensitive G protein, leading to the generation of the second messenger inositol 1,4,5‐trisphosphate [Ins(1,4,5)P 3 ]. We have generated two C‐terminal truncation mutants of the δ‐opioid receptor lacking the final 15 or 37 amino acids and examined their coupling to PLC and adenylyl cyclase. d ‐[Pen 2,5 ]‐enkephalin (DPDPE) mediated Ins(1,4,5)P 3 formation and cyclic AMP inhibition was measured in whole cells and assayed using radioreceptor mass assays. DPDPE produced a time‐ and dose‐dependent increase in Ins(1,4,5)P 3 mass formation in Chinese hamster ovary (CHO) cells expressing the δ wt , δ 15 , and δ 37 receptors. As the C terminus was truncated, the time to maximum stimulation (15 s in CHOδ wt , 60 s in CHOδ 15 , and 120 s in CHOδ 37 ) increased and removal of the C terminus resulted in a prompt return to basal Ins(1,4,5)P 3 levels. Whereas the dose‐response curves to Ins(1,4,5)P 3 formation and cyclic AMP inhibition remained largely unaffected by C‐terminal truncation, there were large differences in the pEC/IC 50 values, with cyclic AMP inhibition being the more potent, perhaps indicating G iα coupling to adenylyl cyclase and G iβ/γ coupling to PLC. Collectively, these data indicate that the C terminus of the δ‐opioid receptor is unimportant in the acute coupling to adenylyl cyclase but may have a role to play in PLC coupling. We hypothesize that an intact C terminus is required to allow normal “strong” coupling of receptor to G i and that truncation weakens this link as reflected in an increased time to peak. In addition, if the coupling is weak, the acute response to agonist stimulation rapidly uncouples.