Activation of TRPA1 by luminal stimuli induces EP₄-mediated anion secretion in human and rat colon

Abstract

Kaji I, Yasuoka Y, Karaki S, Kuwahara A. Activation of TRPA1 by luminal stimuli induces EP4-mediated anion secretion in human and rat colon. Am J Physiol Gastrointest Liver Physiol 302: G690-G701, 2012. First published December 29, 2011; doi:10.1152/ajpgi.00289.2011 physiology, anion and fluid secretion is an important function for host defense and is induced by changes in the luminal environment. The transient receptor potential A1 (TRPA1) channel is considered to be a chemosensor in several sensory tissues. Although the function of TRPA1 has been studied in GI motility, its contribution to the transepithelial ion transport system has rarely been discussed. In the present study, we investigated the secretory effect of the potential TRPA1 agonist allyl isothiocyanate (AITC) in rat and human colon using an Ussing chamber. The mucosal application of AITC (10 Ϫ6 -10 Ϫ3 M) induced Cl Ϫ and HCO 3 Ϫ secretion in a concentrationdependent manner, whereas the serosal application induced a significantly weaker effect. AITC-evoked anion secretion was attenuated by tissue pretreatment with piroxicam and prostaglandin (PG) E2; however, this secretion was not affected by TTX, atropine, or extracellular Ca 2ϩ depletion. These experiments indicate that TRPA1 activation induces anion secretion through PG synthesis, independent of neural pathways in the colon. Further analysis also indicates that AITCevoked anion secretion is mediated mainly by the EP4 receptor subtype. The magnitude of the secretory response exhibited segmental heterogeneity in rat colon. Real-time PCR analysis showed the segmental difference was corresponding to the differential expression of EP4 receptor and cyclooxygenase-1 and -2. In addition, RT-PCR, in situ hybridization, and immunohistochemical studies showed TRPA1 expression in the colonic epithelia. Therefore, we conclude that the activation of TRPA1 in colonic epithelial cells is likely involved in the host defense mechanism through rapid anion secretion. colonic chemosensing; prostaglandin E2 THE EPITHELIUM OF THE GASTROINTESTINAL (GI) tract functions not only as a gate for water and nutrients but as a barrier between the luminal and internal environments. Recent studies have suggested that luminal sensory molecules in the small intestine influence nutrient metabolism and local physiological responses (1, 31, 32). Molecular identification of sensory receptors, such as olfactory, taste, and thermo-receptors, which are part of the transient receptor potential (TRP) family, has helped to elucidate chemical-sensing systems that detect the luminal state. However, the physiological roles of these receptors in colonic ion transport have rarely been investigated at the organ level. In particular, transepithelial anion secretion followed by fluid secretion is regulated by diverse systems, including the nervous, endocrine, and immune systems (4, 17), and is considered an important function for host defense. Therefore, experiments at the tissue or organ levels are important for understanding the contribution of ...

Epithelial transient receptor potential ankyrin 1 (TRPA1)-dependent adrenomedullin upregulates blood flow in rat small intestine

“…More recently, considerable attention has been given to the presence of TRPA1 in IE cells. Kaji et al (23,24) detected TRPA1 mRNA and protein by RT-PCR and immunohistochemistry in human and rat epithelium isolated from intestinal mucosa, and Pool et al (43) reported on TRPA1 immunosignals in mouse IE cells. The former study showed that AITC and an herbal ingredient, thymol, evoked electrogenic anion secretion from colonic epithelium segments in a TRPA1-dependent manner, although it is still unclear which cell types were stimulated by TRPA1 agonists because the study used unpurified epithelial preparations.…”

“…Natural products, especially medicinal and culinary herbs such as chili pepper, mustard oil, and menthol, are known to stimulate some of these TRP channels. In recent years there has been a growing interest in elucidating the role of TRP channels in gastrointestinal physiology, including intestinal motility, secretion, and visceral sensation (23,24,39,53). However, the physiological implications of TRP channels in intestinal blood flow (IBF) remain largely unexplored.…”

Effect of free thymol on differential gene expression in gastric mucosa of the young pig

“…In cell cultures, thymol activates the thermal/ irritant-responsive TRPA1 (Lee et al, 2008;Kaji et al, 2011), the warmth-sensing TRPV3 (Xu et al, 2006) and the coldsensing TRPM8 (Ortar et al, 2012). Activation of TRPA1 by luminal stimuli induces anion secretion in colon enterocytes (Kaji et al, 2012). Thymol also induces anion secretion from porcine jejunal epithelium in the Ussing chambers (Boudry and Perrier, 2008).…”

TRPA1: A Gatekeeper for Inflammation

“…TRPA1 expression has also been detected in whole intestinal tissue samples, suggesting that it is expressed in cells intrinsic to the gut (107, 108). Indeed, functional expression of TRPA1 was detected in intrinsic neurons of the intestine, as well as in nonneuronal enterochromaffin cells,which are mucosal endocrine cells that line the intestine (109, 110).…”