High affinity binding of Y-25130 for serotonin 3 receptor

The binding of Y-25130 on serotonin 3 (5-HT3) receptors was evaluated by examining its effect on 3H-BRL 43694 (3H-granisetron) binding to rat cerebral cortex membranes in comparison with those of granisetron, ondansetron and metoclopramide. Y-25130, granisetron, ondansetron, metoclopramide, 5-HT and 2-methyl-5-HT displaced the specific binding of 3H-granisetron to the synaptosomal membranes in a concentration-dependent manner. The rank order of potency for inhibition of 3H-granisetron binding by the test compounds was Y-25130≅granisetron > ondansetron> 2-methyl- 5-HT≅5-HT≅metoclopramide. To determine the manner of interaction between Y-25130 and 5-HT3 receptors, Scatchard analysis of 3H-granisetron specific binding to the membranes of the cerebral cortex in the absence or presence of various concentrations of Y-25130 was performed. It was indicated that Y-25130 exerted a typical competitive-type inhibition of 3H-granisetron binding. The present study indicates that Y-25130 binds competitively to 5-HT3 receptors with high affinity.