MOBILIZATION OF INTRACELLULAR CA2+ AND STIMULATION OF CYCLIC-AMP PRODUCTION BY KAPPA-OPIOID RECEPTORS EXPRESSED IN XENOPUS OOCYTES

The intracellular metabotropic pathway, following kappa opioid receptor activation, was investigated in the Xenopus oocyte translation system. When oocytes were injected with cRNA for kappa opioid receptor cDNA, U50488H rarefy 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 kappa 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 Bowing 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 kappa opioid receptors mobilize intracellular Ca2+ 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.