Activation of Delta Opioid Receptors Induces Receptor Insertion and Neuropeptide Secretion

Here we describe a novel mechanism for plasma membrane insertion of the delta opioid receptor (DOR). In small dorsal root ganglion neurons, only low levels of DORs are present on the cell surface, in contrast to high levels of intracellular DORs mainly associated with vesicles containing calcitonin gene-related peptide (CGRP). Activation of surface DORs caused Ca²⁺ release from IP₃-sensitive stores and Ca²⁺ entry, resulting in a slow and long-lasting exocytosis, DOR insertion, and CGRP release. In contrast, membrane depolarization or activation of vanilloid and P2Y₁ receptors induced a rapid DOR insertion. Thus, DOR activation induces a Ca²⁺-dependent insertion of DORs that is coupled to a release of excitatory neuropeptides, suggesting that treatment of inflammatory pain should include blockade of DORs.