RELATIONSHIP BETWEEN BINDING-AFFINITY AND FUNCTIONAL-ACTIVITY OF NOCICEPTIN ORPHANIN FQ/

The relationship between binding affinity and functional activity of n ociceptin/orphanin FQ binding was studied in brain membranes, membrane s of Chinese hamster ovary cells transfected with ORL1, and intact CHO -ORL1 cells. Binding affinities were compared with potency for the sti mulation of [S-35]GTP gamma S binding in cell membranes, and inhibitio n of forskolin-stimulated cAMP accumulation in intact cells. Binding w as conducted with [H-3]14-Tyr-nociceptin, and in brain or cell membran es the affinity was found to be 50-100 pM. The binding of [H-3]14-Tyr- nociceptin was found to be regulated by Na+ and GTP, as expected for a n opioid-like receptor. In intact cells, saturation produced a curvili near Scatchard Plot, Non-linear analysis indicated two states of the r eceptor, with the vast majority of binding being to a low affinity sta te of approximately 8 nM. This low affinity component is consistent wi th the lower potency derived from the inhibition of cAMP accumulation, stimulation of [S-35]GTP gamma S binding, and other functional assays .