A dysfunction of the Na(+)/H(+) exchanger isoform 3 (NHE3) significantly contributes to the reduced salt absorptive capacity of the inflamed intestine. We previously reported a strong decrease in the NHERF family member PDZK1 (NHERF3), which binds to NHE3 and regulates its function in a mouse model of colitis. The present study investigates whether a causal relationship exists between the decreased PDZK1 expression and the NHE3 dysfunction in human and murine intestinal inflammation. Biopsies from the colon of patients with ulcerative colitis, murine inflamed ileal and colonic mucosa, NHE3-transfected Caco-2BBe colonic cells with short hairpin RNA (shRNA) knockdown of PDZK1, and Pdzk1-gene-deleted mice were studied. PDZK1 mRNA and protein expression was strongly decreased in inflamed human and murine intestinal tissue as compared to inactive disease or control tissue, whereas that of NHE3 or NHERF1 was not. Inflamed human and murine intestinal tissues displayed correct brush border localization of NHE3 but reduced acid-activated NHE3 transport activity. A similar NHE3 transport defect was observed when PDZK1 protein content was decreased by shRNA knockdown in Caco-2BBe cells or when enterocyte PDZK1 protein content was decreased to similar levels as found in inflamed mucosa by heterozygote breeding of Pdzk1-gene-deleted and WT mice. We conclude that a decrease in PDZK1 expression, whether induced by inflammation, shRNA-mediated knockdown, or heterozygous breeding, is associated with a decreased NHE3 transport rate in human and murine enterocytes. We therefore hypothesize that inflammation-induced loss of PDZK1 expression may contribute to the NHE3 dysfunction observed in the inflamed intestine.

Trafficking, brush border membrane (BBM) retention, and signal-specific regulation of the Na+/H+ exchanger NHE3 is regulated by Na+/H+ Exchanger Regulatory Factor (NHERF) family of PDZ-adapter proteins, which enable the formation of multiprotein complexes. It is unclear, however, what determines signal specificity of the very homologous NHERFs. We studied the association of NHE3, as well as NHERF1 (EBP50), NHERF2 (E3KARP) and NHERF3 (PDZK1) with lipid rafts in murine small intestinal BBM and their possible association with signaling molecules. NHE3 was found to partially associate with glycosphingolipid-enriched microdomains in the native BBM, and NHE3 raft association had an impact on NHE3 transport activity as well as on second-messenger-dependent regulation in vivo. NHERF1, 2 and 3 were differentially distributed to rafts and non-rafts, with NHERF2 being most raft-associated and NHERF3 entirely non-raft associated. A search for other signalling molecules that are implicated in regulating NHE3 through a NHERF interaction, cGMP-dependent kinase II, which together with NHERF2 is essential for guanylin/heat stable enterotoxin of E.coli (STa)-mediated NHE3 inhibition in the intestine, was found exclusively lipid-raft associated. In conclusion, the differential association of the NHERFs, as well as kinases, with the raft-associated and the non-raft fraction of NHE3 in the brush border membrane is likely one component of the differential and signal-specific NHE3 regulation by the different NHERFs.

Background/Aims: Trafficking, brush border membrane (BBM) retention, and signal-specific regulation of the Na+/H+ exchanger NHE3 is regulated by the Na+/H+ Exchanger Regulatory Factor (NHERF) family of PDZ-adaptor proteins, which enable the formation of multiprotein complexes. It is unclear, however, what determines signal specificity of these NHERFs. Thus, we studied the association of NHE3, NHERF1 (EBP50), NHERF2 (E3KARP), and NHERF3 (PDZK1) with lipid rafts in murine small intestinal BBM. Methods: Detergent resistant membranes (“lipid rafts”) were isolated by floatation of Triton X-incubated small intestinal BBM from a variety of knockout mouse strains in an Optiprep step gradient. Acid-activated NHE3 activity was measured fluorometrically in BCECF-loaded microdissected villi, or by assessment of CO2/HCO3- mediated increase in fluid absorption in perfused jejunal loops of anethetized mice. Results: NHE3 was found to partially associate with lipid rafts in the native BBM, and NHE3 raft association had an impact on NHE3 transport activity and regulation in vivo. NHERF1, 2 and 3 were differentially distributed to rafts and non-rafts, with NHERF2 being most raft-associated and NHERF3 entirely non-raft associated. NHERF2 expression enhanced the localization of NHE3 to membrane rafts. The use of acid sphingomyelinase-deficient mice, which have altered membrane lipid as well as lipid raft composition, allowed us to test the validity of the lipid raft concept in vivo. Conclusions: The differential association of the NHERFs with the raft-associated and the non-raft fraction of NHE3 in the brush border membrane is one component of the differential and signal-specific NHE3 regulation by the different NHERFs.

Asthma is a chronic condition with unknown pathogenesis, and recent evidence suggests that enhanced airway epithelial chloride (Cl-) secretion plays a role in the disease. However, the molecular mechanism underlying Cl- secretion and its relevance in asthma pathophysiology remain unknown. To determine the role of the solute carrier family 26, member 9 (SLC26A9) Cl- channel in asthma, we induced Th2-mediated inflammation via IL-13 treatment in wild-type and Slc26a9-deficient mice and compared the effects on airway ion transport, morphology, and mucus content. We found that IL-13 treatment increased Cl- secretion in the airways of wild-type but not Slc26a9-deficient mice. While IL-13-induced mucus overproduction was similar in both strains, treated Slc26a9-deficient mice exhibited airway mucus obstruction, which did not occur in wild-type controls. In a study involving healthy children and asthmatics, a polymorphism in the 3' UTR of SLC26A9 that reduced protein expression in vitro was associated with asthma. Our data demonstrate that the SLC26A9 Cl- channel is activated in airway inflammation and suggest that SLC26A9-mediated Cl- secretion is essential for preventing airway obstruction in allergic airway disease. These results indicate that SLC26A9 may serve as a therapeutic target for airway diseases associated with mucus plugging.

BackgroundIntestinal NHE3 is scaffolded and differentially regulated by Na+/H+Exchanger Regulatory Factor (NHERF) PDZ‐adaptors. NHE3 partially resides in lipid rafts of the Brush Border Membrane (BBM).AimTo investigate if there is a cross talk between NHERFs and membrane rafts, specifically if NHERFs associate differentially with the raft and non‐raft fraction of NHE3, and whether they influence the function and distribution of NHE3 in these microdomains.Methods and ResultsMurine BBM was detergent‐solubilised and lipid rafts isolated by density gradient floatation. NHE3 was partially, NHERF2 strongly and NHERF1 weakly raft‐associated, and NHERF3 exclusively in the non‐raft fraction. In absence of NHERF2, raft‐associated NHE3 was strongly decreased. Increasing the membrane sphingomyelin/ceramide ratio, increased NHE3‐dependent small intestinal fluid absorption in vivo, as well as overall NHE3 in the lipid rafts, suggesting a positive correlation between NHE3 function and raft association.ConclusionsIn murine small intestinal BBM, NHE3 differentially associates with the different NHERFs in the raft and non‐raft fraction. NHE3 raft‐association is NHERF2‐dependent. NHE3 and NHERF raft‐association and function are modulated by changes in the lipidic environment. This suggests that PDZ‐scaffolding proteins are involved in the retention of membrane proteins within lipid raft platforms.

Key points The mucosa of the proximal duodenum is regularly exposed to the strong acid of gastric juice, and acid damage causes peptic ulceration and bleeding. The epithelial cells of the duodenum protect themselves against acid‐induced chemical damage by secreting bicarbonate into the lumen and by regulating their intracellular pH, but the molecular mechanisms of duodenal pHi control are incompletely understood. We have found a high expression of the electroneutral sodium bicarbonate transporter Slc4a7 (NBCn1) in the basolateral membrane of duodenal villous enterocytes. Genetic knockout of Slc4a7 resulted in a strong defect in duodenocyte pHi recovery from acid loads, and reduced bicarbonate secretory rates. This suggests that the electroneutral sodium bicarbonate cotransporter Slc4a7 is a major import mechanism for HCO3− from the blood into the duodenal epithelial cells. Defects in this transporter may severely endanger duodenal mucosal integrity Abstract Duodenocyte pHi control and HCO3− secretion protects the proximal duodenum against damage by gastric acid. The molecular details of duodenocyte pH control are not well understood. A selective duodenal expression (within the upper GI tract) has been reported for the electroneutral Na+:HCO3− cotransporter NBCn1 (Slc4a7). We aimed to determine the role of NBCn1 and NBCe2 in duodenocyte intracellular pH regulation as well as basal and agonist‐stimulated duodenal bicarbonate secretion (JHCO3−), exploiting mouse models of genetic slc4a7 and slc4a5 disruption. Basal and forskolin (FSK)‐stimulated JHCO3− was measured by single‐pass perfusion in the duodenum of slc4a7−/− and slc4a7+/+ as well as slc4a5−/− and slc4a5+/+ mice in vivo, and by pH‐stat titration in isolated duodenal mucosa in vitro. Duodenocyte HCO3− uptake rates were fluorometrically assessed after acidification of intact villi and of isolated duodenocytes. Slc4a7−/− mice displayed significantly lower basal and FSK‐stimulated duodenal HCO3− secretion than slc4a7+/+ littermates in vivo. FSK‐stimulated HCO3− secretion was significantly reduced in slc4a7−/− isolated duodenal mucosa. Na+‐ and HCO3−‐dependent base uptake rates were significantly decreased in slc4a7−/− compared with slc4a7+/+ villus duodenocytes when measured in intact villi. Carbonic anhydrase (CA)‐mediated CO2 hydration played no apparent role as a HCO3− supply mechanism for basal or FSK‐stimulated secretion in the slc4a7+/+ duodenum, but was an important alternative HCO3− supply mechanism in the slc4a7−/− duodenum. NBCe2 (Slc4a5) displayed markedly lower duodenal mRNA expression levels, and its disruption did not interfere with duodenal HCO3− secretion. The electroneutral Na+:HCO3− cotransporter NBCn1 (slc4a7) is a major duodenal HCO3− importer that supplies HCO3− during basal and FSK‐stimulated HCO3− secretion.

BACKGROUND & AIMSDiarrhea results from reduced net fluid and salt absorption caused by an imbalance in intestinal absorption and secretion. The bulk of sodium and water absorption in the intestine is mediated by Na(+)/H(+) exchanger 3 (NHE3), located in the luminal membrane of enterocytes. We investigated the effect of lysophosphatidic acid (LPA) on Na(+)/H(+) exchanger activity and Na(+)-dependent fluid absorption in the intestine.METHODSWe analyzed the effects of LPA on fluid absorption in intestines of wild-type mice and mice deficient in Na(+)/H(+) exchanger regulatory factor 2 (NHERF2; Nherf2(-/-)) or LPA(2) (Lpa(2)(-/-)). Roles of LPA(5) and NHERF2 were determined by analysis of heterologous expression.RESULTSUnder basal conditions, LPA increased fluid absorption in an NHE3-dependent manner and restored the net fluid loss in a mouse model of acute diarrhea. Expression of the LPA receptor LPA(5) was necessary for LPA-induced stimulation of NHE3 activity in colonic epithelial cells. Stimulation of NHE3 by the LPA-LPA(5) signaling required coexpression of NHERF2, which interacted with LPA(5). LPA-mediated intestinal fluid absorption was impaired in Nherf2(-/-) mice, demonstrating the requirement for NHERF2 in LPA(5) activity. However, fluid absorption was unaltered in Lpa(2)(-/-) mice. LPA stimulated NHE3 and fluid absorption in part by increasing NHE3 protein abundance at the brush border membrane of intestinal epithelial cells.CONCLUSIONSLPA is a potent stimulant of NHE3 and fluid absorption in the intestine, signaling through LPA(5). Regulation by LPA(5) depends on its interaction with NHERF2. LPA might be useful in the treatment of certain diarrheal diseases.

Trafficking and regulation of the epithelial brush border membrane (BBM) Na+/H+ exchanger 3 (NHE3) in the intestine involves interaction with four different members of the NHERF family in a signal-dependent and possibly segment-specific fashion. The aim of this research was to study the role of NHERF2 (E3KARP) in intestinal NHE3 BBM localization and second messenger-mediated and receptor-mediated inhibition of NHE3. Immunolocalization of NHE3 in WT mice revealed predominant microvillar localization in jejunum and colon, a mixed distribution in the proximal ileum but localization near the terminal web in the distal ileum. The terminal web localization of NHE3 in the distal ileum correlated with reduced acid-activated NHE3 activity (fluorometrically assessed). NHERF2 ablation resulted in a shift of NHE3 to the microvilli and higher basal fluid absorption rates in the ileum, but no change in overall NHE3 protein or mRNA expression. Forskolin-induced NHE3 inhibition was preserved in the absence of NHERF2, whereas Ca2+ ionophore- or carbachol-mediated inhibition was abolished. Likewise, Escherichia coli heat stable enterotoxin peptide (STp) lost its inhibitory effect on intestinal NHE3. It is concluded that in native murine intestine, the NHE3 adaptor protein NHERF2 plays important roles in tethering NHE3 to a position near the terminal web and in second messenger inhibition of NHE3 in a signal- and segment-specific fashion, and is therefore an important regulator of intestinal fluid transport.

CFTR has been recognized to function as both an anion channel and a key regulator of Slc26 anion transporters in heterologous expression systems. Whether this regulatory relationship between CFTR and Slc26 transporters is seen in native intestine, and whether this effect is coupled to CFTR transport function or other features of this protein, has not been studied. The duodena of anesthetized CFTR-, NHE3-, Slc26a6-, and Scl26a3-deficient mice and wild-type (WT) littermates were perfused, and duodenal bicarbonate (HCO(3)(-)) secretion (DBS) and fluid absorptive or secretory rates were measured. The selective NHE3 inhibitor S1611 or genetic ablation of NHE3 significantly reduced fluid absorptive rates and increased DBS. Slc26a6 (PAT1) or Slc26a3 (DRA) ablation reduced the S1611-induced DBS increase and reduced fluid absorptive rates, suggesting that the effect of S1611 or NHE3 ablation on HCO(3)(-) secretion may be an unmasking of Slc26a6- and Slc26a3-mediated Cl(-)/HCO(3)(-) exchange activity. In the absence of CFTR expression or after application of the CFTR(inh)-172, fluid absorptive rates were similar to those of WT, but S1611 induced virtually no increase in DBS, demonstrating that CFTR transport activity, and not just its presence, is required for Slc26-mediated duodenal HCO(3)(-) secretion. A functionally active CFTR is an absolute requirement for Slc26-mediated duodenal HCO(3)(-) secretion, but not for Slc26-mediated fluid absorption, in which these transporters operate in conjunction with the Na(+)/H(+) exchanger NHE3. This suggests that Slc26a6 and Slc26a3 need proton recycling via NHE3 to operate in the Cl(-) absorptive mode and Cl(-) exit via CFTR to operate in the HCO(3)(-) secretory mode.

The switch of intestinal Slc26 exchangers from anion absorptive to HCO 3 (cid:1) secretory mode is dependent on CFTR anion channel function. Am J Physiol Cell Physiol 298: C1057–C1065, 2010. has been recognized to function as both an anion channel and a key regulator of Slc26 anion transporters in heterologous expression systems. Whether this regulatory relationship between CFTR and Slc26 transporters is seen in native intestine, and whether this effect is coupled to CFTR transport function or other features of this protein, has not been studied. The duodena of anesthetized CFTR-, NHE3-, Slc26a6-, and Scl26a3-deficient mice and wild-type (WT) littermates were perfused, and duodenal bicarbonate (HCO 3 (cid:1) ) secretion (DBS) and fluid absorptive or secretory rates were measured. The selective NHE3 inhibitor S1611 or genetic ablation of NHE3 significantly reduced fluid absorptive rates and increased DBS. Slc26a6 (PAT1) or Slc26a3 (DRA) ablation reduced the S1611-induced DBS increase and reduced fluid absorptive rates, suggesting that the effect of S1611 or NHE3 ablation on HCO 3 (cid:1) secretion may be an unmasking of Slc26a6- and Slc26a3-mediated Cl (cid:1) /HCO 3 (cid:1) exchange activity. In the absence of CFTR expression or after application of the CFTR(inh)-172, fluid absorptive rates were similar to those of WT, but S1611 induced virtually no increase in DBS, demonstrating that CFTR transport activity, and not just its presence, is required for Slc26-mediated duodenal HCO 3 (cid:1) secretion. A functionally active CFTR is an absolute requirement for Slc26-mediated duodenal HCO 3 (cid:1) secretion, but not for Slc26-medi-ated fluid absorption, in which these transporters operate in conjunc-tion with the Na (cid:2) /H (cid:2) exchanger NHE3. This suggests that Slc26a6 and Slc26a3 need proton recycling via NHE3 to operate in the Cl (cid:1) absorptive mode and Cl (cid:1) exit via CFTR to operate in the HCO 3 (cid:1) secretory mode. A in CFTR-deficient duodenum, basal DBS was significantly lower than in WT duodenum, and no significant S1611-stimulated DBS was observed. This indicates that CFTR expression is essential for Slc26-mediated HCO 3 (cid:1) secretion. fluid absorption was not significantly different in CFTR- deficient duodenum, and S1611 inhibited fluid absorption in both WT and CFTR-deficient duodenum. The time course of inhibition of fluid absorption by S1611 was slower in CFTR-deficient than WT duodenum, yet a 60% inhibition was achieved in the the reason for the lack of S1611- mediated stimulation of DBS was a necessity of CFTR for Slc26-mediated 3 secretion, not an inactivity of NHE3 in CFTR-deficient duodenum.

We have demonstrated that Na+/H+ exchanger regulatory factor 1 (NHERF1) overexpression in CFBE41o-cells induces a significant redistribution of F508del cystic fibrosis transmembrane conductance regulator (CFTR) from the cytoplasm to the apical membrane and rescues CFTR-dependent chloride secretion. Here, we observe that CFBE41o-monolayers displayed substantial disassembly of actin filaments and that overexpression of wild-type (wt) NHERF1 but not NHERF1-Delta Ezrin-Radixin-Moesin (ERM) increased F-actin assembly and organization. Furthermore, the dominant-negative band Four-point one, Ezrin, Radixin, Moesin homology (FERM) domain of ezrin reversed the wt NHERF1 overexpression-induced increase in both F-actin and CFTR-dependent chloride secretion. wt NHERF1 overexpression enhanced the interaction between NHERF1 and both CFTR and ezrin and between ezrin and actin and the overexpression of wt NHERF1, but not NHERF1-Delta ERM, also increased the phosphorylation of ezrin in the apical region of the cell monolayers. Furthermore, wt NHERF1 increased RhoA activity and transfection of constitutively active RhoA in CFBE41o-cells was sufficient to redistribute phospho-ezrin to the membrane fraction and rescue both the F-actin content and the CFTR-dependent chloride efflux. Rho kinase (ROCK) inhibition, in contrast, reversed the wt NHERF1 overexpression-induced increase of membrane phospho-ezrin, F-actin content, and CFTR-dependent secretion. We conclude that NHERF1 overexpression in CFBE41o-rescues CFTR-dependent chloride secretion by forming the multiprotein complex RhoA-ROCK-ezrin-actin that, via actin cytoskeleton reorganization, tethers F508del CFTR to the cytoskeleton stabilizing it on the apical membrane.

G A A b st ra ct s of calcitonin on ion transport in IECs. Human colonic T84 cells grown on Transwell inserts were utilized as an in-vitro model of IECs. Chloride secretion was assessed by the measurement of short circuit current (Isc) across T84 monolayers mounted in Ussing chambers. We first examined the expression of CTR in IECs. Real time QRT-PCR and western blot analysis demonstrated the expression of CTR in T84 cells. Exposure of T84 cells to calcitonin from the basolateral but not apical side significantly increased Isc (a change of 287 ± 48 μA/cm2 from the baseline). Stimulation of Isc by calcitonin was dose-dependent (1-100 nM) and was completely blocked by the CTR antagonist, CT8-32. In addition, the increase in Isc was blocked by replacing chloride in the bath solutions with equal amount of gluconate (95 ± 6% reduction, P < 0.01) and was significantly inhibited by 10 μM of the specific CFTR inhibitor, CFTR127inh, (88 ± 9% reduction, P < 0.01) indicating the involvement of CFTR chloride channel in CT-induced effects. To further investigate the signaling pathways involved, we examined calcitonin-induced Isc in the presence of the chelator of [Cai], BAPTA-AM and PKA inhibitor, H89. Preincubation with 20 μMof BAPTAAM or 10μM H89 for 45 minutes significantly reduced calcitonin-induced Isc indicating the involvement of both Ca++and PKA-dependent pathways (58±13% reduction, P < 0.01 and 55±7%, P < 0.01, respectively). Simultaneous inhibition of both Ca++ and PKA pathways had an additive effect on the CT-induced stimulation of Isc (78 ± 8% reduction, P < 0.01). In conclusion, calcitonin-induced short circuit current appears to be mediated by CTR via direct activation of the CFTR channel and is Ca++ and PKA-dependent. This novel study showing the expression of calcitonin receptor in intestinal epithelial cells provides further insights into the molecular mechanisms underlying calcitonin-induced diarrhea. (Supported by NIDDK and Dept of Veteran Affairs).

PEPT1 function in mouse intestine has not been assessed by means of electrophysiology and methods to assess its role in intracellular pH and fluid homeostasis. Therefore, the effects of the dipeptide glycilsarcosin (Gly-Sar) on jejunal fluid absorption and villous enterocyte intracellular pH (pH(i)) in vivo, as well as on enterocyte[(14)C]Gly-Sar uptake, short-circuit current (I(sc)) response, and enterocyte pH(i) in vitro were determined in wild-type and PEPT1-deficient mice and in mice lacking PEPT1. Immunohistochemistry for PEPT1 failed to detect any protein in enterocyte apical membranes in Slc15a1(-/-) animals. Saturable Gly-Sar uptake in Slc15a1(-/-) everted sac preparations was no longer detectable. Similarly, Gly-Sar-induced jejunal I(sc) response in vitro was abolished. The dipeptide-induced increase in fluid absorption in vivo was also abolished in animals lacking PEPT1. Since PEPT1 acts as an acid loader in enterocytes, enterocyte pH(i) was measured in vivo by two-photon microscopy in SNARF-4-loaded villous enterocytes of exteriorized jejuni in anesthetized mice, as well as in BCECF-loaded enterocytes of microdissected jejunal villi. Gly-Sar-induced pH(i) decrease was no longer observed in the absence of PEPT1. A reversal of the proton gradient across the luminal membrane did not significantly diminish Gly-Sar-induced I(sc) response, whereas a depolarization of the apical membrane potential by high K(+) or via Na(+)-K(+)-ATPase inhibition strongly diminished Gly-Sar-induced I(sc) responses. This study demonstrates for the first time that proton-coupled electrogenic dipeptide uptake in the native small intestine, mediated by PEPT1, relies on the negative apical membrane potential as the major driving force and contributes significantly to intestinal fluid transport.

The four members of the NHERF (Na+/H+exchanger regulatory factor) family of PDZ adapter proteins bind to a variety of membrane transporters and receptors and modulate membrane expression, mobility, interaction with other proteins, and the formation of signaling complexes. All four family members are expressed in the intestine. The CFTR (cystic fibrosis transmembrane regulator) anion channel and the Na+/H+exchanger NHE3 (Na/H exchanger‐ isoform 3) are two prominent binding partners to this PDZ‐adapter family, which are also known key players in the regulation of intestinal electrolyte and fluid transport. Experiments in heterologous expression systems have provided a number of mechanistic models how NHERF protein interactions can affect the function of their targets at the molecular level. Recently, NHERF1, 2, and 3 knockout mice have become available, and this review summarizes the reports on electrolyte and fluid transport regulation in the native intestine of these mice.

BackroundThe molecular mechanisms for inflammatory diarrhea are multifactorial and incompletely understood.AimWe investigated the expression, localization and function of the major intestinal sodium absorptive transporter, the Na+/H+ exchanger NHE3, as well as its regulatory PDZ‐adapter proteins NHERF1 and PDZK1, in the small and large intestine of mice after induction of a CD45RBhigh transfer colitis.ResultsAfter colitis induction, TNF‐alpha levels were increased both in the inflamed colon and microscopically normal‐appearing small intestine. NHE3 mRNA expression was upregulated in the colon and unaltered in the small intestine, NHE3 protein expression and localization in the brush border membrane (BBM) was not altered, but acid‐activated NHE3 transport rates in small intestinal villous and colonic surface cells were severely decreased, and fluid absorption in vivo was decreased in the small intestine. PDZK1 mRNA expression was downregulated, whereas that of NHERF1 was not altered. Glucocorticoid treatment of colitic mice for 4 days decreased colonic mucosal cytokine expression and increased PDZK1 expression as well as fluid absorption.ConclusionWe suggest that during immune‐mediated intestinal inflammation, NHE3 BBM protein abundance is normal, but the regulation of its transport activity is disturbed. PDZK1 downregulation during inflammation may be one factor responsible for inflammation‐associated NHE3 dysfunction

G A A b st ra ct s before and after medication were analyzed for small intestinal injuries. NSAID treatment significantly increased the mean number of mucosal breaks and reddened lesions per subject in the Control-group, from 0.1±0.3 to 15.8±71.5 and from 4.0±3.9 to 10.0±10.3 respectively; but only up from 0.1±0.3 to 4.2±7.8 and from 5.4±6.3 to 9.2±6.6 in the Rebamipide-group. The percentage of subjects with at least one mucosal break at post-treatment was also higher in the Control-group (63%) than in the Rebamipide-group (47%); (NS). The percentage of subjects with post-treatment increases in reddened lesions ≥ 10 was significantly higher in the Control-group (46%) than in the Rebamipide-group (14%); (P=0.04). Conclusion: Rebamipide administration reduced the incidence of small intestinal lesions induced by twoweek administration of diclofenac sodium. Further studies are warranted to determine whether a higher rebamipide dosage can further protect against NSAID-induced small intestinal mucosal breaks.