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This Article Full Text Full Text (PDF) All Versions of this Article: 291/5/G868    most recent 00023.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Sandu, C. Articles by Lang, F. Search for Related Content PubMed PubMed Citation Articles by Sandu, C. Articles by Lang, F.

LIVER AND BILIARY TRACT

Impaired intestinal NHE3 activity in the PDK1 hypomorphic mouse

¹Department of Physiology I, University of Tübingen, Germany; ²Division of Digestive Diseases, Departments of Medicine and Physiology, Emory University School of Medicine, Atlanta, Georgia; and ³MRC Phosphorylation Unit, University of Dundee, Dundee, Scotland

Submitted 17 January 2006 ; accepted in final form 31 May 2006

In vitro experiments have demonstrated the stimulating effect of serum- and glucocorticoid-inducible kinase (SGK)1 on the activity of the Na⁺/H⁺ exchanger (NHE3). SGK1 requires activation by phosphoinositide-dependent kinase (PDK)1, which may thus similarly play a role in the regulation of NHE3-dependent epithelial electrolyte transport. The present study was performed to explore the role of PDK1 in the regulation of NHE3 activity. Because mice completely lacking functional PDK1 are not viable, hypomorphic mice expressing 20% of PDK1 (pdk1^hm) were compared with their wild-type littermates (pdk1^wt). NHE3 activity in the intestine and PDK1-overexpressing HEK-293 cells was estimated by utilizing 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein fluorescence for the determination of intracellular pH. NHE activity was reflected by the Na⁺-dependent pH recovery from an ammonium prepulse (pH_NHE). The pH changes after an ammonium pulse allowed the calculation of cellular buffer capacity, which was not significantly different between pdk1^hm and pdk1^wt mice. pH_NHE was in pdk1^hm mice, only 30 ± 6% of the value obtained in pdk1^wt mice. Conversely, pH_NHE was 32 ± 7% larger in PDK1-overexpressing HEK-293 cells than in HEK-293 cells expressing the empty vector. The difference between pdk1^hm and pdk1^wt mice and between PDK1-overexpressing and empty vector-transfected HEK cells, respectively, was completely abolished in the presence of the NHE3 inhibitor S3226 (10 µM). In conclusion, defective PDK1 expression leads to significant impairment of NHE3 activity in the intestine, pointing to a role of PDK1-dependent signaling in the regulation of NHE-mediated electrolyte transport.

phosphatidylinositol 3-kinase; transport regulation; Na⁺/H⁺ exchanger; pH regulation

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