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1 Department of Surgery, Yale University , School of Medicine, New Haven, CT, USA
2 Department of Surgery, Yale University , School of Medicine, New Haven, CT, USA; Department of Cellular and Molecular Physiology, Yale University , School of Medicine, New Haven, CT, USA; Institute of Physiology, University of Zurich, Zurich, Switzerland
3 Department of Surgery, Yale University , School of Medicine, New Haven, CT, USA; Department of Cellular and Molecular Physiology, Yale University , School of Medicine, New Haven, CT, USA
* To whom correspondence should be addressed. E-mail: john.geibel{at}yale.edu.
Previous studies have shown that gastric glands express at least sodium-hydrogen exchanger (NHE) isoforms 1-4. Our aim was to study NHE-3 localization in rat parietal cells, and to investigate the functional activity of an apical membrane NHE-3 isoform in parietal cells of rats.
Western blot analysis and immunohistochemistry showed expression of NHE-3 in rat stomach colocalizing the protein in parietal cells together with the 
-subunit of the H+,K+-ATPase. Functional studies in luminally perfused gastric glands demonstrated the presence of an apically NHE isoform sensitive to low concentrations of EIPA. Intracellular pH measurements in parietal cells conducted in omeprazole pretreated superfused gastric glands showed a Na+-dependent proton extrusion pathway that was inhibited by both low concentrations of EIPA and the NHE-3 specific inhibitor S3226. This pathway for proton extrusion had a higher activity in resting glands and was inhibited upon stimulation of histamine induced H+, K+-ATPase proton extrusion. We conclude that the NHE-3 isoform located on the apical membrane of parietal cells offers an additional pathway for proton secretion, under resting conditions. Furthermore, the gastric NHE-3 appears to work under resting conditions and inactivates during periods of H+, K+-ATPase activity.
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