5-HT induces duodenal mucosal bicarbonate secretion via cAMP- and Ca2+-dependent signaling pathways and 5-HT4 receptors in mice.
In previous studies, we have found that 5-hydroxytryptamine (5-HT) is a potent stimulant of duodenal mucosal bicarbonate secretion (DMBS) in mice. The aim of the present study was to determine the intracellular signaling pathways and 5-HT receptor subtypes involved in 5-HT-induced DMBS. Bicarbonate secretion by murine duodenal mucosa was examined in vitro in Ussing chambers. 5-HT receptor involvement in DMBS was inferred from pharmacological studies by using selective 5-HT receptor antagonists and agonists. The expression of 5-HT(4) receptor mRNA in duodenal mucosa and epithelial cells was analyzed by RT-PCR. cAMP-dependent signaling pathway inhibitors MDL-12330A, Rp-cAMP, and H-89 and Ca(2+)-dependent signaling pathway inhibitors verapamil and W-13 markedly reduced 5-HT-stimulated duodenal bicarbonate secretion and short-circuit current (I(sc)), whereas cGMP-dependent signaling pathway inhibitors NS-2028 and KT-5823 failed to alter these responses. Both SB-204070 and high-dose ICS-205930 (selective 5-HT(4) receptor antagonists) markedly inhibited 5-HT-stimulated bicarbonate secretion and I(sc), whereas methiothepine (5-HT(1) receptor antagonist), ketanserin (5-HT(2) receptor antagonist), and a low concentration of ICS-205930 (5-HT(3) receptor antagonist) had no effect. RS-67506 (partial 5-HT(4) receptor agonist) concentration-dependently increased bicarbonate secretion and I(sc), whereas 5-carboxamidotryptamine (5-HT(1) receptor agonist), alpha-methyl-5-HT (5-HT(2) receptor agonist), and phenylbiguanide (5-HT(3) receptor agonist) did not significantly increase bicarbonate secretion or I(sc). RT-PCR analysis confirmed the expression of 5-HT(4) receptor mRNA in murine duodenal mucosa and epithelial cells. These results demonstrate that 5-HT regulates DMBS via both cAMP- and Ca(2+)-dependent signaling pathways and 5-HT(4) receptors located in the duodenal mucosa and/or epithelial cells.
Division of Gastroenterology, Department of Medicine, School of Medicine, University of California, San Diego, CA 92103, USA.
Bi-Guang
BG
Tuo
Zachary
Z
Sellers
Petra
P
Paulus
Kim E
KE
Barrett
Jon I
JI
Isenberg
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D000242:Cyclic AMP / Q000502:physiology*; D004146:Dioxanes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004386:Duodenum / Q000187:drug effects / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D010880:Piperidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D044422:Receptors, Serotonin, 5-HT4 / Q000187:drug effects*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012701:Serotonin / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*; D013449:Sulfonamides / Q000494:pharmacology
D001639:Bicarbonates; D004146:Dioxanes; D007473:Ion Channels; D010880:Piperidines; D012333:RNA, Messenger; D017366:Serotonin Receptor Agonists; D013449:Sulfonamides; C084858:SB 204070A; D044422:Receptors, Serotonin, 5-HT4; C107556:RS 67506; D012701:Serotonin; D000242:Cyclic AMP