PROPERTIES OF A KAPPA-OPIOID RECEPTOR EXPRESSED IN CHO CELLS - INTERACTION WITH MULTIPLE G-PROTEINS IS NOT SPECIFIC FOR ANY INDIVIDUAL G-ALPHA SUBUNIT AND IS SIMILAR TO THAT OF OTHER OPIOID RECEPTORS

The purpose of the present study was to examine the coupling pattern of a recently cloned K-opioid receptor stably transfected in CHO cells to individual G(alpha) subunits with subsequent comparison to that observed previously for delta- and mu-opioid receptors. Data presented in the current study indicate the successful stable expression of a kappa-opioid receptor in CHO cells. This is supported by experiments in which ligands with selectivity for kappa-, but not delta- or mu-opioid receptors demonstrated high affinity for the expressed receptor and were able to potently and efficaciously produce inhibition of adenylyl cyclase activity. In addition, only kappa-opioid agonists were able to induce dose-dependent increases in the incorporation of [P-32]azidoanilido-GTP into four G(alpha) subunits, three of which were identified as Gi(3 alpha), Gi(2 alpha) and Go(2 alpha). Further, the amount of kappa-opioid agonists required to induce 50% maximal labeling of any individual G(alpha) subunit was similar. Although kappa-opioid agonists produced equivalent maximal labeling of Gi(3 alpha), Gi(2 alpha), and Go(2 alpha), significantly less agonist-induced labeling was observed for an unknown G-protein designated as G?(alpha). Although these results are slightly different than those observed previously for both delta- and mu-opioid receptors, it appears that all opioid receptors stably transfected in CHO cells interact with multiple G-proteins and that this coupling is not selective for any invidivual G(alpha) subunit.