Morphine promotes phosphorylation of the human δ-opioid receptor at serine 363

Abstract After prolonged stimulation, the δ-opioid receptor becomes desensitized by regulatory mechanisms such as receptor phosphorylation, internalization and down-regulation. In this study, we demonstrate that morphine treatment causes phosphorylation of S 363 in the C-terminus of the human δ-opioid receptor. Morphine-mediated phosphorylation reached 53 ± 8% of maximum deltorphin II-mediated phosphorylation. Phosphorylation of S 363 may contribute to δ-opioid receptor desensitization by morphine.