Abstract
On the basis of differences in the potencies and intrinsic activity of 5-HT4 receptor agonists in different biological models it has been suggested that there is heterogeneity among 5-HT4 receptors. Here, we report the molecular cloning of several 5-HT4 receptor splice variants in mouse, rat, and human brain. Our data suggest that the differences in efficacy of 5-HT4 ligands on 5-HT4 receptor-mediated responses in several tissues is due to differences in coupling efficiency rather than to the presence of different 5-HT4 receptor isoforms.