Leucine-2-alanine enkephalin induced delta opioid receptors internalization expressed stably in CHO cells

AIM: To characterize the internalization of delta opioid receptors (DOR) st ably expressed in Chinese hamster ovary (CHO) cells and the role of the C-t erminal in this process. METHODS: Receptor membrane anchoring was shown by immunofluorescence microscopy. Receptor internalization was assessed by mea suring the radioligand binding resistant to the acid-buffer wash. RESULTS: Originally, all the wildtype (CHO-W) and C-truncated (CHO-T) DOR expressed were localized to the membrane. Agonist [H-3] leucine3-alanine enkephalin ( LAE) but not the antagonist [3H]diprenorphine (Dip) induced rapid receptor internalization. The internalization of C-truncated DOR in CHO-T was simila r to that of the wild-type in maximal level, but climbed up more slowly. DO R internalization was extracellular osmolarity- and temperature-sensitive. Pertussis toxin and universal protein kinase inhibitor staurosporine had no effect on it. CONCLUSION: DOR internalization is an agonist and clathrin-c oated pits dependent, but post-receptor cellular signal transduction indepe ndent process; moreover, the C-terminal of DOR, not engaged in membrane anc horing, affects the initialization of DOR internalization.