title: Fast modulation of μ-opioid receptor (MOR) recycling is mediated by receptor agonists.
abstract: The μ-opioid receptor (MOR) is a member of the G protein-coupled receptor family and the main target of endogenous opioid neuropeptides and morphine. Upon activation by ligands, MORs are rapidly internalized via clathrin-coated pits in heterologous cells and dissociated striatal neurons. After initial endocytosis, resensitized receptors recycle back to the cell surface by vesicular delivery for subsequent cycles of activation. MOR trafficking has been linked to opioid tolerance after acute exposure to agonist, but it is also involved in the resensitization process. Several studies describe the regulation and mechanism of MOR endocytosis, but little is known about the recycling of resensitized receptors to the cell surface. To study this process, we induced internalization of MOR with [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin (DAMGO) and morphine and imaged in real time single vesicles recycling receptors to the cell surface. We determined single vesicle recycling kinetics and the number of receptors contained in them. Then we demonstrated that rapid vesicular delivery of recycling MORs to the cell surface was mediated by the actin-microtubule cytoskeleton. Recycling was also dependent on Rab4, Rab11, and the Ca(2+)-sensitive motor protein myosin Vb. Finally, we showed that recycling is acutely modulated by the presence of agonists and the levels of cAMP. Our work identifies a novel trafficking mechanism that increases the number of cell surface MORs during acute agonist exposure, effectively reducing the development of opioid tolerance.
authors.affiliation: Department of Anatomy and Neurobiology, School of Medicine, University of Puerto Rico, San Juan, Puerto Rico.
authors.forename: Cristina
authors.initials: C
authors.lastname: Roman-Vendrell
authors.forename: Y Joy
authors.initials: YJ
authors.lastname: Yu
authors.forename: Guillermo Ariel
authors.initials: GA
authors.lastname: Yudowski
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D022163:Clathrin-Coated Vesicles / Q000235:genetics / Q000378:metabolism; D003342:Corpus Striatum / Q000166:cytology / Q000378:metabolism*; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology*; D006801:Humans; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism; D024701:Myosin Type V / Q000235:genetics / Q000378:metabolism; D009218:Myosins / Q000235:genetics / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000819:agonists* / Q000235:genetics / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020695:rab4 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D000099193:rab11 GTP-Binding Proteins
chemical_list: D000701:Analgesics, Opioid; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D018995:Myosin Heavy Chains; D024701:Myosin Type V; D009218:Myosins; D017450:Receptors, Opioid, mu; D020691:rab GTP-Binding Proteins; D020695:rab4 GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins; C505832:MYO5B protein, human; C101826:Myo5b protein, rat