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MUCOSAL BIOLOGY

Demonstration of a functional apical sodium hydrogen exchanger in isolated rat gastric glands

Departments of ¹Surgery and ²Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06511; and ³Institute of Physiology, University of Zurich, CH-8057 Zurich, Switzerland

Submitted 9 April 2003 ; accepted in final form 2 August 2003

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 apical NHE isoform sensitive to low concentrations of 5-ethylisopropyl amiloride (EIPA). Intracellular pH measurements in parietal cells conducted in omeprazole-pretreated superfused gastric glands showed an Na⁺-dependent proton extrusion pathway that was inhibited both by low concentrations of EIPA and by the NHE-3 specific inhibitor S3226. This pathway for proton extrusion had a higher activity in resting glands and was inhibited on 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.

gastric acid secretion; intracellular pH; sodium-hydrogen exchanger-3

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