Mosapride stimulates human 5-HT₄-serotonin receptors in the heart

Mosapride (4-amino-5-chloro-2-ethoxy-N-[[4-[(4-fluorophenyl) methyl]-2-morpholinyl]-methyl] benzamide) is a potent agonist at gastrointestinal 5-HT₄ receptors. Mosapride is an approved drug to treat several gastric diseases. We tested the hypothesis that mosapride also stimulates 5-HT₄ receptors in the heart. Mosapride increased the force of contraction and beating rate in isolated atrial preparations from mice with cardiac overexpression of human 5-HT₄-serotonin receptors (5-HT₄-TG). However, it is inactive in wild-type mouse hearts (WT). Mosapride was less effective and potent than serotonin in raising the force of contraction or the beating rate in 5-HT₄-TG. Only in the presence of cilostamide (1 μM), a phosphodiesterase III inhibitor, mosapride, and its primary metabolite time dependently raised the force of contraction under isometric conditions in isolated paced human right atrial preparations (HAP, obtained during open heart surgery). In HAP, mosapride (10 μM) reduced serotonin-induced increases in the force of contraction. Mosapride (10 µM) shifted the concentration-response curves to serotonin in HAP to the right. These data suggest that mosapride is a partial agonist at 5-HT₄-serotonin receptors in HAP.