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Am J Physiol Cell Physiol. 2015 Apr 15;308(8):C650-6. doi: 10.1152/ajpcell.00355.2014. Epub 2015 Feb 4.

Chronic and selective inhibition of basolateral membrane Na-K-ATPase uniquely regulates brush border membrane Na absorption in intestinal epithelial cells.

Author information

1
Department of Biochemistry and Microbiology, University of Cincinnati, Cincinnati, Ohio;
2
Section of Digestive Diseases, West Virginia University, Morgantown, West Virginia;
3
Department of Clinical and Translational Sciences, Joan C. Edwards School of Medicine, Marshall University, Huntington, West Virginia; and.
4
Center for Cardiovascular and Respiratory Sciences, West Virginia University, Morgantown, West Virginia.
5
Department of Clinical and Translational Sciences, Joan C. Edwards School of Medicine, Marshall University, Huntington, West Virginia; and sundaramu@marshall.edu.

Abstract

Na-K-ATPase, an integral membrane protein in mammalian cells, is responsible for maintaining the favorable intracellular Na gradient necessary to promote Na-coupled solute cotransport processes [e.g., Na-glucose cotransport (SGLT1)]. Inhibition of brush border membrane (BBM) SGLT1 is, at least in part, due to the diminished Na-K-ATPase in villus cells from chronically inflamed rabbit intestine. The aim of the present study was to determine the effect of Na-K-ATPase inhibition on the two major BBM Na absorptive pathways, specifically Na-glucose cotransport and Na/H exchange (NHE), in intestinal epithelial (IEC-18) cells. Na-K-ATPase was inhibited using 1 mM ouabain or siRNA for Na-K-ATPase-α1 in IEC-18 cells. SGLT1 activity was determined as 3-O-methyl-D-[(3)H]glucose uptake. Na-K-ATPase activity was measured as the amount of inorganic phosphate released. Treatment with ouabain resulted in SGLT1 inhibition at 1 h but stimulation at 24 h. To further characterize this unexpected stimulation of SGLT1, siRNA silencing was utilized to inhibit Na-K-ATPase-α1. SGLT1 activity was significantly upregulated by Na-K-ATPase silencing, while NHE3 activity remained unaltered. Kinetics showed that the mechanism of stimulation of SGLT1 activity was secondary to an increase in affinity of the cotransporter for glucose without a change in the number of cotransporters. Molecular studies demonstrated that the mechanism of stimulation was not secondary to altered BBM SGLT1 protein levels. Chronic and direct silencing of basolateral Na-K-ATPase uniquely regulates BBM Na absorptive pathways in intestinal epithelial cells. Specifically, while BBM NHE3 is unaffected, SGLT1 is stimulated secondary to enhanced affinity of the cotransporter.

KEYWORDS:

Na-K-ATPase; Na-glucose cotransporter; SGLT1; intestinal inflammation; ouabain

PMID:
25652450
PMCID:
PMC4398852
DOI:
10.1152/ajpcell.00355.2014
[Indexed for MEDLINE]
Free PMC Article

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