Interaction of agonist peptide [3H]Tyr-D-Ala-Phe-Phe-NH2 with μ-opioid receptor in rat brain and CHO-μ/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) cells expressing the rat CL-receptor. In rat brain, [H-3]TAPP labeled a single 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 demonstrated 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-specific binding make this radioligand a useful tool for labeling the native and cloned mu-opioid receptor. (C) 1998 Elsevier Science Inc.