No abstract

Cyclic guanosine 3′,5′-monophosphate (cGMP)-dependent protein kinases (cGKs) mediate cellular signaling induced by nitric oxide and cGMP. Mice deficient in the type II cGK were resistant to Escherichia coli STa, an enterotoxin that stimulates cGMP accumulation and intestinal fluid secretion. The cGKII-deficient mice also developed dwarfism that was caused by a severe defect in endochondral ossification at the growth plates. These results indicate that cGKII plays a central role in diverse physiological processes.

BackgroundProbiotics are proposed to positively modulate the intestinal epithelial barrier formed by intestinal epithelial cells (IECs) and intercellular junctions. Disruption of this border alters paracellular permeability and is a key mechanism for the development of enteric infections and inflammatory bowel diseases (IBDs).Methodology and Principal FindingsTo study the in vivo effect of probiotic Escherichia coli Nissle 1917 (EcN) on the stabilization of the intestinal barrier under healthy conditions, germfree mice were colonized with EcN or K12 E. coli strain MG1655. IECs were isolated and analyzed for gene and protein expression of the tight junction molecules ZO-1 and ZO-2. Then, in order to analyze beneficial effects of EcN under inflammatory conditions, the probiotic was orally administered to BALB/c mice with acute dextran sodium sulfate (DSS) induced colitis. Colonization of gnotobiotic mice with EcN resulted in an up-regulation of ZO-1 in IECs at both mRNA and protein levels. EcN administration to DSS-treated mice reduced the loss of body weight and colon shortening. In addition, infiltration of the colon with leukocytes was ameliorated in EcN inoculated mice. Acute DSS colitis did not result in an anion secretory defect, but abrogated the sodium absorptive function of the mucosa. Additionally, intestinal barrier function was severely affected as evidenced by a strong increase in the mucosal uptake of Evans blue in vivo. Concomitant administration of EcN to DSS treated animals resulted in a significant protection against intestinal barrier dysfunction and IECs isolated from these mice exhibited a more pronounced expression of ZO-1.Conclusion and SignificanceThis study convincingly demonstrates that probiotic EcN is able to mediate up-regulation of ZO-1 expression in murine IECs and confer protection from the DSS colitis-associated increase in mucosal permeability to luminal substances.

Boehringer Ingelheim.

Most segments of the gastrointestinal tract secrete HCO3−, but the molecular nature of the secretory mechanisms has not been identified. We had previously speculated that the regulator for intestinal electrogenic HCO3− secretion is the cystic fibrosis transmembrane regulator (CFTR) channel. To prove this hypothesis, we have now measured HCO3− secretion by pH‐stat titration, and recorded the electrical parameters of in vitro duodenum, jejunum and ileum of mice deficient in the gene for the CFTR protein (‘CF‐mice’) and their normal littermates. Basal HCO3− secretory rates were reduced in all small intestinal segments of CF mice. Forskolin, PGE2, 8‐bromo‐cAMP and VIP (cAMP‐dependent agonists), heat‐stable enterotoxin of Escherichia coli (STa), guanylin and 8‐bromo‐cGMP (cGMP‐dependent agonists) and carbachol (Ca2+ dependent) stimulated both the short‐circuit current (ISC) and the HCO3− secretory rate (JHCO3‐) in all intestinal segments in normal mice, whereas none of these agonists had any effect on JHCO3‐ in the intestine of CF mice. To investigate whether Cl−–HCO3− exchangers, which have been implicated in mediating the response to some of these agonists in the intestine, were similarly active in the small intestine of normal and CF mice, we studied CF gradient‐driven 36Cl− uptake into brush‐border membrane (BBM) vesicles isolated from normal and CF mouse small intestine. Both the time course and the peak value for 4,4’‐diisothiocyanostilbene‐2’,2‐disulphonic acid (DIDS)‐inhibited 36Cl− uptake was similar in normal and CF mice BBM vesicles. In summary, the results demonstrate that the presence of the CFTR channel is necessary for agonist‐induced stimulation of electrogenic HCO3− secretion in all segments of the small intestine, and all three intracellular signal transduction pathways stimulate HCO3− secretion exclusively via activation of the CFTR channel.

Epithelial barrier characterization in occludin-deficiency points against an essential barrier function of occludin within the tight junction strands or to a substitutional redundancy of single tight junction molecules like occludin. A dramatic change in gastric morphology and secretory function indicates that occludin is involved in gastric epithelial differentiation.

Although being equal in short-term efficacy and overall tolerability our results suggest a better gastrointestinal tolerability for iron sucrose. Larger trials are mandatory to prove a possible advantage of iron sucrose in short- and long-term efficacy as well as in tolerability over iron sulfate in the management of IDA in IBD.

SLC26A6 (PAT1, CFEX) is an anion exchanger that is expressed on the apical membrane of the kidney proximal tubule and the small intestine. Modes of transport mediated by SLC26A6 include Cl−/formate exchange, Cl−/HCO3− exchange, and Cl−/oxalate exchange. To study its role in kidney and intestinal physiology, gene targeting was used to prepare mice lacking Slc26a6. Homozygous mutant Slc26a6−/− mice appeared healthy and exhibited a normal blood pressure, kidney function, and plasma electrolyte profile. In proximal tubules microperfused with a low-HCO3−/high-Cl− solution, the baseline rate of fluid absorption ( Jv), an index of NaCl transport under these conditions, was the same in wild-type and null mice. However, the stimulation of Jv by oxalate observed in wild-type mice was completely abolished in Slc26a6-null mice ( P < 0.05). Formate stimulation of Jv was partially reduced in null mice, but the difference from the response in wild-type mice did not reach statistical significance. Apical membrane Cl−/base exchange activity, assayed with the pH-sensitive dye BCPCF in microperfused proximal tubules, was decreased by 58% in Slc26a6−/− animals ( P < 0.001 vs. wild types). In the duodenum, the baseline rate of HCO3− secretion measured in mucosal tissue mounted in Ussing chambers was decreased by ∼30% ( P < 0.03), whereas the forskolin-stimulated component of HCO3− secretion was the same in wild-type and Slc26a6−/− mice. We conclude that Slc26a6 mediates oxalate-stimulated NaCl absorption, contributes to apical membrane Cl−/base exchange in the kidney proximal tubule, and also plays an important role in HCO3− secretion in the duodenum.