5-Hydroxytryptamine inhibits Na absorption and stimulates C1 secretion across canine tracheal epithelial sheets


J. Tamaoki, First Dt;partment of Medicine. Tokyo Wtimen's Medical College, 8–1 Kawada-Cho, Shinjuku, Tokyo 162, Japan.


Background 5-Hydrozytryptamine (5-HT) can be released from mast cells and platelets through an IgE-dependent mechanism and may play a role in the pathogenesis of allergic bronchoconstriction. However, the effect of 5-HT on ion transport by airway epithelium remains uncertain.

Objective To determine whether 5-HT alters electrical and ion transport properties of C1-secreting epilhelia and, if so, what subtype of 5-HT receptors is involved, we studied canine tracheal epithelium under short-circuit conditions in vitro.

Methods Canine tracheal mucosa was mounted in Lucite half-chambers and the responses of short-circuit current (lsc), transepithelial potential difference (PD) and tissue conductance (G) were measured. ln addition, ion fluxes were directly measured using 22Na and 36C1.

Results Mucosal addition of 5-HT caused a rapid increase in lsc, which was accompanied by the increases in PD and G, whereas submucosal 5-HT had no effect. In the presence of amiloride, 5-HT and its receptor agonists dose-dependently increased lsc, with the rank order of potency being 5-HT > α-methyl-5-HT>2-methyl-5HT>5-carboxamidotryptamine. The effect of 5-HT was inhibited by ketanserin and spiperone but not by ondansetron. 5-HT increased C1 flux from the submucosa to the mucosa with a slight inhibition of Na flux to the opposite direction.

Conclusion 5-HT inhibits airway epithelial Na absorption and stimulates C1 secretion. The latter action predominates the former and is mediated by 5-HT2 receptors. These effects may result in the increase in water movement toward the airway lumen.