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 o f a recently cloned K-opioid receptor stably transfected in CHO cells to individual G(alpha) subunits with subsequent comparison to that obs erved previously for delta- and mu-opioid receptors. Data presented in the current study indicate the successful stable expression of a kapp a-opioid receptor in CHO cells. This is supported by experiments in wh ich ligands with selectivity for kappa-, but not delta- or mu-opioid r eceptors demonstrated high affinity for the expressed receptor and wer e able to potently and efficaciously produce inhibition of adenylyl cy clase activity. In addition, only kappa-opioid agonists were able to i nduce dose-dependent increases in the incorporation of [P-32]azidoanil ido-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 kapp a-opioid agonists required to induce 50% maximal labeling of any indiv idual G(alpha) subunit was similar. Although kappa-opioid agonists pro duced 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 t ransfected in CHO cells interact with multiple G-proteins and that thi s coupling is not selective for any invidivual G(alpha) subunit.