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Background information. Celiac disease is a chronic inflammatory disorder of the small bowel induced in genetically susceptible subjects by gluten ingestion. Diarrhoea, weight loss and malabsorption represent the major clinical presentation of the disease. Here we examined the possible alteration in the expression and localization of water channels [AQPs (aquaporins)] and some solute transporters in duodenal mucosa of celiac disease patients. Duodenal biopsies from untreated celiacs, treated celiacs, healthy controls and disease controls were considered in the present study. The expressions of some AQPs and transporter mRNAs in human duodenal biopsies were determined by semi‐quantitative RT—PCR (reverse transcription PCR) and real‐time RT—PCR. The localization of AQPs 3, 7 and 10 and of SGLT1 (Na+/glucose co‐transporter 1), PEPT1 (H+/oligopeptide transporter 1) and NHE3 (Na+/H+ exchanger 3) was evaluated by immunohistochemistry. Results. AQPs 3, 7, 10 and 11, SGLT, PEPT and NHE, CFTR (cystic fibrosis transmembrane conductance regulator) and NKCC (Na‐K‐2Cl co‐transporter) mRNAs were expressed in duodenal biopsies of healthy controls, treated celiac patients and disease controls. The expression of transcripts was virtually absent in duodenal biopsies of untreated celiac disease patients except for CFTR and NKCC. In healthy controls, immunohistochemistry revealed a labelling in the apical membrane of surface epithelial cells of the duodenum. The immunolabelling was heavily reduced or absent in untreated celiac patients, while it was normal in patients consuming a gluten‐free diet for at least 12 months. Conclusions. Our results indicate that the main routes for water and solute absorption are deficient in celiac disease and may play a role in the onset of malabsorption symptoms.

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L-lactate transport mechanism across rat jejunal enterocyte was investigated using isolated membrane vesicles. In basolateral membrane vesicles L-lactate uptake is stimulated by an inwardly directed H+ gradient; the effect of the pH difference is drastically reduced by FCCP, pCMBS and phloretin, while furosemide is ineffective. The pH gradient effect is strongly temperature dependent. The initial rate of the proton gradient-induced lactate uptake is saturable with respect to external lactate with a K(m) of 39.2 +/- 4.8 mM and a Jmax of 8.9 +/- 0.7 nmoles mg protein-1 sec-1. A very small conductive pathway for L-lactate is present in basolateral membranes. In brush border membrane vesicles both Na+ and H+ gradients exert a small stimulatory effect on lactate uptake. We conclude that rat jejunal basolateral membrane contains a H(+)-lactate cotransporter, whereas in the apical membrane both H(+)-lactate and Na(+)-lactate cotransporters are present, even if they exhibit a low transport rate.

Outwardly oriented H+ gradients greatly enhanced thiamine transport rate in brush border membrane vesicles from duodenal and jejunal mucosa of adult Wistar rats. At a gradient pHin5:pHout7.5, thiamine uptake showed an overshoot, which at 15 sec was three times as large as the uptake observed in the absence of the gradient. Under the same conditions, the binding component of uptake accounted for only 10-13% of intravesicular transport. At the same gradient, the Km and Jmax values of the saturable component of the thiamine uptake curve after a 6 sec incubation time were 6.2 +/- 1.4 microM and 14.9 +/- 3 pmol.mg-1 protein.6 sec-1 respectively. These values were about 3 and 5 times higher, respectively, than those recorded in the absence of H+ gradient. The saturable component of the thiamine antiport had a stoichiometric thiamine: H+ ratio of 1:1 and was inhibited by thiamine analogues, guanidine, guanidine derivatives, inhibitors of the guanidine/H+ antiport, and imipramine. Conversely, the guanidine/H+ antiport was inhibited by unlabeled thiamine and thiamine analogues; omeprazole caused an approximately fourfold increase in thiamine transport rate. In the absence of H+ gradient, changes in transmembrane electrical potential did not affect thiamine uptake. At equilibrium, the percentage membrane-bound thiamine taken up was positively correlated with the pH of the incubation medium, and increased from about 10% at pH 5 to 99% at pH 9.