Mobilization of intracellular Ca 2+ and stimulation of cyclic AMP production by κ opioid receptors expressed in Xenopus oocytes

Abstract

The intracellular metabotropic pathway, following κ opioid receptor activation, was investigated in the Xenopus oocyte translation system. When oocytes were injected with cRNA for κ opioid receptor cDNA, U50488H rarely evoked phospholipase C-mediated, oscillatory Cl − current responses. However, after the oocytes were incubated with staurosporine, both the occurrence and the amplitude of U50488H-evoked responses were increased. The U50488H-evoked response was antagonized by naloxone and inhibited by pretreatment of the oocytes with pertussis toxin. When oocytes were coinjected with RNAs encoding κ opioid receptor and cystic fibrosis transmembrane conductance regulator (CFTR), treatment of the oocytes with forskolin and 3-isobutyl-1-methylxanthine (IBMX) evoked a smooth-shaped Cl − current flowing through the CFTR channels. The forskolin/IBMX-evoked response was never inhibited but was greatly potentiated in the presence of U50488H, indicating stimulation of adenylyl cyclase by U50488H. This U50488H-induced potentiation of CFTR channel opening was antagonized by naloxone and inhibited by pretreatment with pertussis toxin. These results suggest that κ opioid receptors mobilize intracellular Ca 2+ and stimulate cyclic AMP production by coupling positively to both phospholipase C and adenylyl cyclase via pertussis toxin-sensitive GTP-binding proteins in the oocytes.