Receptor trafficking induced by μ-opioid-receptor phosphorylation

Opiates, including morphine, are widely used drugs for antinociception in clinics. Prolonged treatments of opioids induce both tolerance and dependence, which are the major side effects of opioid therapy. One of the mechanisms for the development of tolerance and dependence is implicated to be opioid-receptor trafficking. Here we review the current understandings of opioid-receptor phosphorylation, endocytosis and desensitization after repeated agonist treatments. Also, the role of G-protein coupled receptor kinases in opioid-receptor phosphorylation is discussed. How to associate these observations to physiological and behavioral changes in animal models and clinics is still under investigation. (C) 2009 Elsevier Ltd. All rights reserved.