CHARACTERIZATION OF [H-3] YM060, A POTENT AND SELECTIVE 5-HT3 RECEPTOR RADIOLIGAND, IN THE CEREBRAL-CORTEX OF RATS

The binding properties of a new radioligand, 3-yl)carbonyl]-4,5,6,7-te trahydro-1H-benzimidazole monohydrochloride ([H-3]YM060), were studied in membranes of the rat cerebral cortex. [H-3]YM060 rapidly associate d with its binding sites in membranes and reversibly dissociated. Satu ration analysis revealed that the specific binding of [H-3]YM060 was s aturable and non-specific binding was low. Scatchard analysis yielded a linear plot, suggesting a single population of binding sites with a dissociation constant (K-d) of 8.4 +/- 0.2 pM (n = 3) and the kinetic K-d determined from the association constant (K-+1) and the dissociati on rate constant (K--1) was similar. The maximum number of binding sit es (B-max) was 37.0 +/- 0.8 fmol/mg protein (n = 3). [H-3]YM060 bindin g was potently and stereospecifically inhibited by serotonin (5-HT)(3) receptor agonists and ant agonists. O ther 5-HT receptor ligands such as 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin), methysergide a nd ketanserin were inactive to inhibit specific binding at 10(-4) M. T hese results suggest that [H-3]YM060 is a highly potent and selective 5-HT3 receptor radioligand and will be useful in the further analysis of 5-HT3 receptors.