Journal
GASTROENTEROLOGY
Volume 135, Issue 5, Pages 1645-1653Publisher
W B SAUNDERS CO-ELSEVIER INC
DOI: 10.1053/j.gastro.2008.07.083
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Funding
- NCI NIH HHS [R01 CA095172, CA-95172] Funding Source: Medline
- NCRR NIH HHS [T32-RR-07004, T32 RR007004] Funding Source: Medline
- NIDDK NIH HHS [R01 DK048816, R56 DK048816, DK48816, DK074459, R29 DK048816, R01 DK054016, DK54016, P01 DK067887, P01 DK067887-030001, R01 DK054016-11] Funding Source: Medline
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Background & Aims: Electroneutral NaCl absorption across small intestine contributes importantly to systemic fluid balance. Disturbances in this process occur in both obstructive and diarrheal. diseases, eg, cystic fibrosis, secretory diarrhea. NaCl absorption involves coupling of Cl-/HCO3- exchanger(s) primarily with Na+/H+ exchanger 3 (Nhe3) at the apical membrane of intestinal epithelia. Identity of the coupling Cl-/HCO3- exchanger(s) was investigated using mice with gene-targeted knockout (KO) of Cl-/HCO3- exchangers: Slc26a3, down-regulated in adenoma (Dra) or Slc26a6, putative anion transporter-1 (Pat-1). Methods: intracellular pH (pH(i)) of intact jejunal villous epithelium was measured by ratiometric microfluoroscopy. Ussing chambers were used to measure transepithelial (NaCl)-Na-22-Cl-36 flux across murine jejunum, a site of electroneutral NaCl absorption. Expression was estimated using immunofluorescence and quantitative polymerase chain reaction. Results: Basal pH(i) of DraKO epithelium, but not Pat-1KO epithelium, was alkaline, whereas pHi in the Nhe3KO was acidic relative to wild-type. Altered pHi was associated with robust Na+/H+ and Cl-/HCO3- exchange activity in the DraKO and Nhe3KO villous epithelium, respectively. Contrary to genetic ablation, pharmacologic inhibition of Nhe3 in wild-type did not alter pHi but coordinately inhibited Dra. Flux studies revealed that Cl- absorption was essentially abolished (>80%) in the DraKO and little changed (20%) in the Pat-1KO jejunum. Net Na+ absorption was unaffected. Immunofluorescence demonstrated modest Dra expression in the jejunum relative to large intestine. Functional and expression studies did not indicate compensatory changes in relevant transporters. Conclusions: These studies provide functional evidence that Dra is the major Cl-/HCO3- exchanger coupled with Nhe3 for electroneutral NaCl absorption across mammalian small intestine.
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