Serotonin-induced contractile responses of esophageal smooth muscle in the house musk shrew (Suncus murinus).

Background: Serotonin (5-hydroxytryptamine, 5-HT) is a regulatory factor in motility of the gastrointestinal tract including the esophagus. Although we proposed that vagal cholinergic and mast cell-derived non-cholinergic components including serotonin coordinately shorten the esophagus, the precise mechanism of serotonin-induced contractions in the suncus esophagus is still unclear. Therefore, the aims of this study were to determine characteristics of contractile responses induced by serotonin and to identify 5-HT receptor subtypes responsible for regulating motility in the suncus esophagus.

Methods: An isolated segment of the suncus esophagus was placed in an organ bath, and longitudinal or circular mechanical responses were recorded using a force transducer.

Key Results: Serotonin evoked contractile responses of the suncus esophagus in the longitudinal direction but not in the circular direction. Tetrodotoxin did not affect the serotonin-induced contractions. Pretreatment with a non-selective 5-HT receptor antagonist or double application of 5-HT and 5-HT receptor antagonists blocked the serotonin-induced contractions. 5-HT and 5-HT receptor agonists, but not a 5-HT receptor agonist, evoked contractile responses in the suncus esophagus.

Conclusion & Inferences: The findings suggest that serotonin induces contractile responses of the longitudinal smooth muscle in the muscularis mucosae of the suncus esophagus that are mediated via 5-HT and 5-HT receptors on muscle cells. The serotonin-induced contractions might contribute to esophageal peristalsis and emetic response.