INTERACTION OF AGONIST PEPTIDE [H-3]TYR-D-ALA-PHE-PHE-NH2 WITH MU-OPIOID RECEPTOR IN RAT-BRAIN AND CHO-MU 1 CELL-LINE/

Opioid receptor binding properties of [H-3]Tyr-D-Ala-Phe-Phe-NH, (TAPP ) were characterized in rat brain and Chinese hamster ovary (CHO) cell s expressing the rat CL-receptor. In rat brain, [H-3]TAPP labeled a si ngle class of opioid sites with a dissociation constant (K-d) of 0.31 nM and maximal number of binding sites (B-max) of 119 fmol/mg protein. In CHO-mu/l cell membranes, the K-d and B-max values were 0.78 nM and 1806 fmol/mg protein, respectively. Binding to rat brain was demonstr ated to be pharmacologically identical to that obtained with CHO-mu/l cell membranes and modulated by Na+ ions and guanine nucleotides. The high affinity and selectivity of [H-3]TAPP together with its low non-s pecific binding make this radioligand a useful tool for labeling the n ative and cloned mu-opioid receptor. (C) 1998 Elsevier Science Inc.