title: Rapid, opioid-sensitive mechanisms involved in transient receptor potential vanilloid 1 sensitization.
abstract: TRPV1 is a nociceptive, Ca2+-selective ion channel involved in the development of several painful conditions. Sensitization of TRPV1 responses by cAMP-dependent PKA crucially contributes to the development of inflammatory hyperalgesia. However, the pathways involved in potentiation of TRPV1 responses by cAMP-dependent PKA remain largely unknown. Using HEK cells stably expressing TRPV1 and the mu opioid receptor, we demonstrated that treatment with the adenylate cyclase activator forskolin significantly increased the multimeric TRPV1 species. Pretreatment with the mu opioid receptor agonist morphine reversed this increased TRPV1 multimerization. FRET analysis revealed that treatment with forskolin did not cause multimerization of pre-existing TRPV1 monomers on the plasma membrane and that intracellular pools of TRPV1 exist mostly as monomers in this model. This suggests that increased TRPV1 multimerization occurred from an intracellular store of inactive TRPV1 monomers. Treatment with forskolin also caused an increase in TRPV1 expression on the plasma membrane not resulting from increased TRPV1 expression, and this rapid TRPV1 translocation was inhibited by treatment with morphine. Thus, potentiation of TRPV1 responses by cAMP-dependent PKA involves plasma membrane insertion of functional TRPV1 multimers formed from an intracellular store of inactive TRPV1 monomers. This potentiation occurs rapidly and can be dynamically modulated by activation of the mu opioid receptor under conditions where cAMP levels are raised, such as with inflammation. Increased translocation and multimerization of TRPV1 channels provide a cellular mechanism for fine-tuning of nociceptive responses that allow for rapid modulation of TRPV1 responses independent of transcriptional changes.
authors.affiliation: School of Pharmacy, The University of Queensland, St Lucia, Queensland 4072, Australia.
authors.forename: Irina
authors.initials: I
authors.lastname: Vetter
authors.forename: Wei
authors.initials: W
authors.lastname: Cheng
authors.forename: Madusha
authors.initials: M
authors.lastname: Peiris
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Wyse
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Roberts-Thomson
authors.forename: Jie
authors.initials: J
authors.lastname: Zheng
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Monteith
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Cabot
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D020536:Enzyme Activators / Q000494:pharmacology; D031541:Fluorescence Resonance Energy Transfer; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D008297:Male; D008954:Models, Biological; D009020:Morphine / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000819:agonists / Q000378:metabolism*
chemical_list: D000701:Analgesics, Opioid; D020536:Enzyme Activators; D017450:Receptors, Opioid, mu; D050916:TRPV Cation Channels; C494482:TRPV1 protein, human; C493922:Trpv1 protein, rat; D005576:Colforsin; D009020:Morphine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases