Opioid receptor binding properties of [3H]Tyr-D-Ala-Phe-Phe-NH2 (TAPP) were characterized in rat brain and Chinese hamster ovary (CHO) cells expressing the rat μ-receptor. In rat brain, [3H]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-μ/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-μ/l cell membranes and modulated by Na+ ions and guanine nucleotides. The high affinity and selectivity of [3H]TAPP together with its low non-specific binding make this radioligand a useful tool for labeling the native and cloned μ-opioid receptor.
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience