TRIS INHIBITS (+)-[3H]SKF-10,047 BINDING TO SIGMA-RECEPTORS

Tris-HCl is the most commonly used buffer in studies of radioligand binding to sigma-receptors, with concentrations as high as 50 or 100 mM often used. We report here that these concentrations of Tris substantially inhibit (+)-[H-3]SKF-10,047 binding to sigma-receptors. The well-established inhibitory effect of Tris-HCl on ligand binding to PCP receptors did not contribute to the presently reported inhibition of (+)-[H-3]SKF-10,047 binding. The IC50 of Tris, determined in the presence of 10 mM potassium phosphate buffer, was 15.4+/-1.2 mM (n=3, pH 8.0, 25-degrees-C, 1 nM radioligand). Equilibrium saturation studies revealed an apparent competitive inhibition of binding.