S1791 R-Type Calcium Channels Mediate Inhibitory Neuromuscular Transmission and Impair Peristalsis In Vitro in the Guinea-Pig Ileum

Abstract

BACKGROUND/AIM: Enterochromaffin (EC) cells are the best characterized subset of enteric endocrine cells and are the main source of 5-hydroxytryptamine (5-HT) in the gut. Previously we have shown an important immuno-endocrine axis in the gut, where CD4+ T cells play a key role in generation of EC cell hyperplasia and in up-regulation of 5-HT production in infection-induced gut inflammation (Gut 2007; 56: 949). However, the role of EC cells/5HT in regulation of inflammation or in host defense in enteric infection remains to be determined. The aim of this study was to investigate the role of 5-HT in the development of infection-induced gut inflammation and in host defense in a model of enteric infection. METHODS: Tryptophan hydroxylase1-deficient mice (TPH1-/-) which lack 5-HT in gut and wild type (TPH1+/+) mice were infected with nematode, Trichuris muris and sacrificed on various days post-infection (pi) to study the worm expulsion, macrophage infiltration by immunohistochemistry, myeloperoxidase (MPO) activity, and cytokines (IL-β,IL-4 and IL13) in colon by ELISA. Role of 5-HT in production of pro-inflammatory mediators was further studied by culturing macrophages harvested from peritoneal cavity of naive TPH1+/ + mice with 5-HT, and assessing IL-1β production after LPS stimulation. RESULTS: Worm expulsion from the intestine was significantly delayed in TPH1-/mice as compared to TPH1+/+ mice in T. muris infection (worm numbers: 24.2±3.8 vs. 40±6.7 in TPH1+/+ vs. TPH1-/mice on day 21 pi; p<0.05). There was significant down-regulation of infiltration of F4/80 positive macrophages in the colon of TPH1-/mice compared to TPH1+/+ mice after infection. We also observed significantly lower MPO activity and IL-1β levels in colon of TPH1-/-mice as compared to TPH1+/+ mice after infection (MPO activity and IL-1β levels were 41.8±5.3 u/mg and 81.3±4.5 pg/mg protein vs. 26.7±4.8 u/mg and 57±3.9 pg/mg protein in TPH1+/+ vs. TPH1-/mice on day 21 pi; p<0.05). There was no significant difference in IL-4 and IL-13 levels in colon between TPH1-/and TPH1+/+ after infection. We also observed higher amount of IL-1β in the culture supernatant of macrophages harvested from TPH1+/+ mice after stimulation with 5-HT. CONCLUSION: These results provide evidence for an important role for EC cells/5-HT in host defense and in generation of gut inflammation in enteric infection. Considering the strategic location of EC cells in gut mucosa and the importance of 5-HT in intestinal homeostasis, these results provide new insights into the mechanisms of gut pathology and host defense which may ultimately lead to improved therapeutic strategies in various gut disorders.