Protein Kinase C Involvement in Homologous Desensitization of δ-Opioid Receptor Coupled to Gi1-Phospholipase C Activation in Xenopus Oocytes

Abstract

We have developed the coexpression system of both δ-opioid receptor (DOR1) and M2-muscarinic receptor (M2) which mediate agonist-evoked currents due to common post-receptor mechanisms including Gi1 and phospholipase C (PLC) activation in Xenopus oocytes reconstituted with Gi1α. The DOR1-currents by 100 nm D-Ser2-leu-enkephalin-Thr6 (DSLET) were selectively desensitized by 10 nm phorbol 12-myristate 13-acetate (PMA). The PMA-desensitization of DSLET-currents was abolished in the presence of calphostin C, a protein kinase C inhibitor, or reversed by an intracellular injection of calcineurin, a protein phosphatase 2B. When a higher concentration (3 μM) of DSLET was used, DSLET-currents were rapidly desensitized by repeated challenges of DSLET itself. However, repeated challenges of 10 μM ACh caused no influence on such DSLET- or M2-currents. The desensitization of DSLET-currents was selectively reversed by protein kinase C inhibitors. Similar results were also obtained with various δ-opioid agonists. These resutls suggest that protein kinase C is involved in the homologous desensitization of δ-opioid receptors.