Characterization of [3H]U69593 binding sites in the rat heart by receptor binding assays

The binding properties of [3H]U69593, a selective k-ligand, in rat heart homogenates were characterized by direct and displacement receptor binding assays. It was found that there are substantial specific [3H]U69593 binding sites in the rat heart. They were saturable, reversible and stereospecific. Both association and dissociation rates were monophasic and the Scatchard plot was linear, indicating a homogeneity of binding sites. The Hill coefficient was close to 1, indicating an absence of cooperativity. The Bmax and Kd were 7.91 fmol/mg and 2.92 nM, respectively. The binding sites were most abundant in the right atrium, followed by right ventricle, left ventricle and left atrium in descending order. The study provides information on the properties and distribution of k-binding sites in the rat heart.