Characterization of [ 3H]YM060, a potent and selective 5-HT 3 receptor radioligand, in the cerebral cortex of rats

Abstract

The binding properties of a new radioligand, [methyl- 3H]-(−)-( R)-5-[(1-methyl-1 H-indol-3-yl)carbonyl]-4,5,6,7-tetrahydro-1 H-benzimidazole monohydrochloride ([ 3H]YM060), were studied in membranes of the rat cerebral cortex. [ 3H]YM060 rapidly associated with its binding sites in membranes and reversibly dissociated. Saturation analysis revealed that the specific binding of [ 3H]YM060 was saturable 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 dissociation rate constant ( K −1) was similar. The maximum number of binding sites ( B max) was 37.0 ± 0.8 fmol/mg protein ( n = 3). [ 3H]YM060 binding was potently and stereospecifically inhibited by serotonin (5-HT) 3 receptor agonists and antagonists. Other 5-HT receptor ligands such as 8-OH-DPAT (8-hydroxy-2-(di- n-propylamino)tetralin), methysergide and ketanserin were inactive to inhibit specific binding at 10 −4 M. These results suggest that [ 3H]YM060 is a highly potent and selective 5-HT 3 receptor radioligand and will be useful in the further analysis of 5-HT 3 receptors.