TY - JOUR T1 - Morphine-Induced μ-Opioid Receptor Desensitization JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1127 LP - 1132 DO - 10.1124/mol.105.013185 VL - 68 IS - 4 AU - Vu C. Dang AU - John T. Williams Y1 - 2005/10/01 UR - http://molpharm.aspetjournals.org/content/68/4/1127.abstract N2 - Morphine has been widely accepted as the opioid agonist that sustains signaling because it does not cause receptor desensitization or internalization. This notion has led to the hypothesis that long-term morphine treatment initiates downstream adaptations that underlie tolerance and dependence. This study uses whole-cell recordings from neurons in the locus ceruleus to measure the potassium current induced by morphine. The results show that morphine does cause short-term desensitization. The desensitization induced by morphine was slower and smaller then that induced by [MET]5-enkephalin (ME). After a brief application of a saturating concentration of ME, the current induced by morphine was smaller, and desensitization was not observed. In tissue taken from morphine-treated animals, the peak current induced by morphine was the same as in untreated animals, but morphine-induced desensitization was facilitated. The results suggest that morphine, like other agonists, can initiate receptor desensitization to decrease signaling. ER -