Prucalopride stimulates 5-HT4 receptors on cholinergic nerves of human colonic longitudinal muscle resulting in contraction

Abstract

Introduction: The mechanisms underlying the colokinetic actions of the selective 5HT4 receptor agonist prucalopride (R093877) are not fully known. Although in vitro studies demonstrated relaxatory smooth muscle 5-HT4 receptors on the circular muscle, involvement of 5HT4 receptors on the longitudinal muscle (LM) has not yet been demonstrated. We aimed to characterise the effects of prucalopride on electrically stimulated human colon LM in vitro. Methods: Human colonic longitudinal muscle strips (mucosa and mesentery removed) were placed in an organ bath set-up (at 37°C, bubbled with carbogen and filled with LNNA (O.lmM)-enriched Krebs-Henseleit solution) for isotonic measurement (2 g). After stabilisation (30min), electrical field stimulation (EFS; lOs pulse trains at Ims width each 3 min at 12Hz and submaximal voltage) was applied, resulting in contractions. After obtaining reproducible contractions upon EFS for 15min (i.e 5 pulses), solvent, GR1l3808 (O.I/LM), atropine (11J-M) or tetrodotoxin (O.3/LM) was added followed by a 15-min incubation period. Then, prucalopride (O.3/LM) was added and the EFS-induced contractions were followed for another 15 min. Results were expressed as percentage of the average EFS-induced contraction before addition of antagonist. Results: Atropine (l/LM) and tetrodotoxin (O.3/LM) almost completely inhibited the EFS-induced response, but GR113808 (O.l/LM) left them unaffected. Prucalopride (O.3/LM) enhanced the EFS-induced contractions by 33 ~ 5.7% (P < 0.05, Student s t-test), but did not affect them after atropine-, tetrodotoxinor GR1l3808-pre-treatment. Conclusions: On the cholinergic nerves of human colon LM, prucalopride stimulates 5HT4 receptors facilitating release of acetylcholine, resulting in contraction. This suggests that 5HT4 receptor-mediated propulsion is due to circular muscle relaxation (previous studies) and longitudinal muscle contraction (present study).