The pharmacophore of 5-HT 3 receptors consists of three components: a carbonyl-containing linking moiety, aromatic / heteroaromatic ring, and a basic center. The carbonyl group is coplanar to the aromatic ring . 5-HT 3 receptor antagonists are more likely to bind in their protonated form.  Docking of a range of antagonists into a homology model of the 5-HT 3 receptor binding site shows a reasonably good agreement with the pharmacophore model and supports the observed differences between species. Studies of granisetron in the binding pocket revealed that the aromatic rings of granisetron lie between W183 and Y234 and the azabiciclic ring between W90 and F226. In this study another energetically favorable location of granisetron was identified, closer to the membrane, on a position that could be a part of a binding/unbinding pathway for the ligand. A similarly located alternative binding site for granisetron has since been identified in another study of the 5-HT 3 receptor.