Characterization of Opioid Binding Sites in Rat Spinal Cord

AbstractBinding sites were characterized in rat whole spinal cord crude membrane preparations using selective labelling techniques with multiple methods of mathematical analysis of experimental curves. Mathematical analysis of single [3H]-[D-Ala2, MePhe4, Gly-ol5] enkephalin (DAGO) saturation curves suggested binding of the [3H]-ligand at one site, while displacement curves of low concentrations of [3H]-DAGO with selective μ-ligands indicated the presence of high- and low-affinity sites. All the [3H]-DAGO curves processed simultaneously by LIGAND analysis showed the presence of high (27%) and low (73%) affinity components, with a total Bmax of 3.19 pmol/g tissue. Eighty percent of [3H]-[D-Ala2, D-Leu5] enkephalin (DADLE) binding was displaced by DAGO with high affinity, indicating that a high percentage of [3H]-DADLE binding was at μ-sites. Saturation curves of [3H]-DADLE after inhibition of μ-sites by unlabelled DAGO (∂-sites) were monophasic with non-linear fitting analysis and the Bmax was 0.90 pmol/g ...