Gz coupling to the rat kappa-opioid receptor.

We have expressed the cloned rat kappa-opioid receptor in human embryonic kidney 293 cells and studied the ability of kappa-selective ligands to inhibit adenylyl cyclase. In transfected 293 cells, activation of the kappa-opioid receptor by U50,488 and the dynorphins resulted in the inhibition of cAMP accumulation. The inhibitory response was sensitive to pertussis toxin and highly selective for kappa-agonists; neither mu- nor delta-opioids were able to activate the kappa-opioid receptor. Upon co-transfection with the alpha subunit of Gz, inhibition of cAMP accumulation by kappa-agonist became refractory to pertussis toxin, indicating that the kappa-opioid receptor can couple to both G(i) and Gz proteins.