1020 - Inducible Nitric Oxide Mediates the Inhibitiion of Coupled Nacl Abosorption in a Mouse Model of Spontaneous Ileitis

Mast Cell Mediated Regulation of Small Intestinal Chloride Malabsorption in SAMP1/YitFc Mouse Model of Spontaneous Chronic Ileitis

“…Likewise, Western blot analysis of DRA BBM protein expression corroborated the kinetic studies and RT-qPCR data establishing that ketotifen treatment restored DRA activity exactly by the same mechanism that downregulated its activity in SAMP1 mice. This finding is comparable to a previous study where inhibition of inducible nitric oxide by L-NIL treatment reversed DRA activity by the same mechanism that was initially responsible for its downregulation in the SAMP1 mouse model of chronic ileitis [ 27 ]. Moreover, in a related study, it was further established that altered affinity of DRA leading to its downregulation in chronic intestinal inflammation was due to increased phosphorylation in its serine and threonine residues, which was also restored back to its normal levels by L-NIL treatment [ 28 ].…”

“…As demonstrated in a previous study [ 27 ] and in this current study, downregulation of Cl:HCO 3 exchange mediated by DRA in the BBM was found to be secondary to the altered affinity of DRA for its substrate chloride rather than an alteration in its maximal velocity of chloride absorption. Western blot confirmed this finding with unaltered expression of DRA in the BBM of villus cells.…”

“…In this animal model, we have previously demonstrated that Cl:HCO 3 exchange was downregulated in ileal villus cell BBM. Moreover, this downregulation of Cl:HCO 3 exchange was found to be secondary to the altered affinity of the Cl:HCO 3 exchanger for chloride [ 27 ]. Furthermore, molecular studies demonstrated that only DRA, but not PAT1, had altered phosphorylation levels at its serine and threonine residues, which likely mediated its altered affinity for chloride [ 28 ].…”

“…These data indicated that DRA, rather than PAT1, is the anion exchanger responsible for chloride malabsorption during chronic ileitis. With regard to Na:H exchange in the same study, Na:H exchange mediated by NHE3 remained unaffected in the BBM of villus cells [ 27 ], which led us to believe that dysregulated traditional NaCl coupled absorption may not be the viable reason for Na and Cl malabsorption leading to diarrhea in the SAMP1 model of chronic ileitis. Given this background and the importance of DRA in the IBD associated malabsorption of chloride, we determined if mast cell mediators could be responsible for the specific downregulation of DRA mediated chloride malabsorption in the SAMP1 model of spontaneous ileitis.…”

Unique Regulation of Intestinal Villus Epithelial Cl−/HCO3− Exchange by Cyclooxygenase Pathway Metabolites of Arachidonic Acid in a Mouse Model of Spontaneous Ileitis

“…SAMP1/YitFc inbred mouse strain, which develops ileitis spontaneously, without chemical, genetic, or immunologic manipulation, is highly relevant to Crohn's-like ileitis [1]. In this model, for the first time, we previously reported the role of inducible nitric oxide (iNO) in inhibiting Cl − /HCO 3 − exchange in the brush border membrane (BBM) of ileal villus cells with no alteration of Na + /H + exchange [27]. In the current study, we have investigated the mechanism of inhibition of Cl − /HCO 3 − exchange and demonstrated the role of arachidonic acid metabolites (AAMs), known to be elevated in the inflamed mucosa, in mediating inhibition of Cl − /HCO 3 − exchange.…”