Evidence for the involvement of a 5-HT4 receptor in the secretory response of human small intestine to 5-HT.

5-Hydroxytryptamine increases transmucosal short-circuit current across human isolated small intestinal mucosa. The competitive 5-HT4 antagonist, DAU 6285 evoked a concentration-dependent, dextral and parallel shift of the concentration-response curve to 5-HT, with no alteration of the maximum response. Schild analysis of this antagonism produced a Schild regression with a slope of 1.00 and an apparent pA2 estimate of 6.17. It appears that a 5-HT4 receptor may mediate the short-circuit current response of human small intestinal mucosa to 5-HT.