Rl-Neuberg-Stra 1, D-30625 Germany. E-mail: [email protected] Abbreviations ACC, acetylcysteine; CCh, carbachol; CFTR, cystic fibrosis transmembrane conductance regulator; FSK, forskolin; GI, gastrointestinal; KO, knock-out; Muc2, mucin two; NBCn1, sodium icarbonate cotransporter; NHE, Na+ + exchanger; Slc, solute carrier; WT, wild-type.Introduction Bicarbonate ions play a major role in intestinal epithelial homeostasis, epithelial transport and mucosal defence against gastric acid inside the upper gastrointestinal (GI) tract (Allen Flemstr?m, 2005; Kaunitz Akiba, 2006; o Seidler Sjoblom, 2012). Lately, a novel role for HCO3 – ions has been delineated inside the expulsion and expansion of mucus granules inside the airways, intestine and reproductive tract (Quinton, 2010b). A defective mucus barrier has been shown to become a risk element for pathogen-mediated mucosal damage inside the colon by each a normal (Johansson et al. 2008; Petersson et al. 2011) and a pathogenic intestinal flora (Bergstrom et al. 2010; Hasnain et al. 2010). The ionic pathways for intestinal HCO3 – transport, which are activated for the duration of acid challenge and are critical for acid defence in the upper GI tract and for formation of a mucus layer within the reduced GI tract, have already been only partly delineated.tert-Butyl 4-bromopicolinate supplier A critical function with the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel within the coordination of agonist-stimulated HCO3 – secretion has been established in each rodent and human intestine (Seidler et al.Methyl 4-bromo-1H-indole-7-carboxylate structure 1997; Pratha et al.PMID:33741133 2000). In addition, apically expressed members on the Slc26 household of anion exchangers are involved in apical HCO3 – extrusion (Tuo et al. 2006; Walker et al. 2009). Nevertheless, the rate-limiting step for HCO3 – secretion may possibly be the uptake and/or generation of HCO3 – ions rather than apical HCO3 – transporter activation (Jacob et al. 2000), and recent studies are in support of this concept (Xiao et al. 2012b). It has been demonstrated that HCO3 – -dependent mucosal defence against luminal acid will not necessarily require HCO3 – to be secreted into the lumen, but doesrequire intact basolateral HCO3 – uptake mechanisms, which are quickly capable to neutralize the protons which have accumulated inside the enterocytes throughout luminal acid exposure (Akiba et al. 2001b). Therefore, the first aim of this study was to assess intracellular pH (pHi ) recovery just after luminal acid exposure in vivo and the significance of NBCn1 for this regulation. The second aim was to study the significance of NBCn1 expression for the luminal acid-induced HCO3 – secretory response. Expression of NBCn1 has also been detected inside the colonic mucosa, albeit at decrease levels than inside the duodenum (Chen et al. 2012). The third aim of your study was thus to obtain insight in to the physiological function of colonic mucosal NBCn1. The experimental approaches employed within this study have been predominantly in vivo experiments, in which we measured the intracellular as well as the surface epithelial pH and the build-up of the colonic mucus layer applying two-photon microscopic approaches in exteriorized, vascularly perfused duodenal and mid-distal colonic mucosa of anaesthetized mice. Additionally, we assessed duodenal and mid-colonic fluid absorption and/or HCO3 – secretory rates in luminally perfused, anaesthetized, acid ase status-controlled NBCn1 knock-out (KO) and wild-type (WT) mice. These experiments have been supplemented by pHi -stat titration of HCO3 – secretory prices in isolated colonic mucosa and i.