title: Morphine promotes rapid, arrestin-dependent endocytosis of mu-opioid receptors in striatal neurons.
abstract: Morphine activates mu-opioid receptors (MORs) without promoting their rapid endocytosis in a number of cell types. A previous study suggested that morphine can drive rapid redistribution of MORs in the nucleus accumbens, but it was not possible in this in vivo study to identify a specific membrane trafficking pathway affected by morphine, to exclude possible indirect actions of morphine via opiate-regulated neural circuitry, or to define the mechanism of this morphine-dependent regulation. In the present study, we addressed these questions using dissociated primary cultures of rat striatal neurons as a model system. Morphine promoted a rapid redistribution of both endogenous and recombinant MORs within 30 min after drug addition to the culture medium. This effect was mediated by rapid endocytosis and occurred in a cell-autonomous manner, as indicated by its detection in cells plated at low density and in cultures in which depolarization was blocked by tetrodotoxin. Morphine-induced endocytosis of MORs was quantitatively similar to that induced by the enkephalin analog D-Ala2-N-Me-Phe4-Glycol5-enkephalin, and endocytosis induced by both ligands was inhibited by a dominant-negative mutant version of arrestin-3 (beta-arrestin-2). These results extend previous in vivo results and indicate that morphine is indeed capable of driving rapid endocytosis of mu-opioid receptors in an important subset of opiate-responsive CNS neurons. They also suggest a cellular mechanism by which beta-arrestins may modulate the physiological effects of morphine in vivo.
authors.affiliation: Department of Psychiatry, University of California, San Francisco, California 94143, USA.
authors.forename: Helena
authors.initials: H
authors.lastname: Haberstock-Debic
authors.forename: Kyung-Ah
authors.initials: KA
authors.lastname: Kim
authors.forename: Y Joy
authors.initials: YJ
authors.lastname: Yu
authors.forename: Mark
authors.initials: M
authors.lastname: von Zastrow
mesh_terms: D000818:Animals; D019393:Arrestin / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects* / Q000502:physiology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D005260:Female; D009020:Morphine / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D019393:Arrestin; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009020:Morphine