Sodium-glucose cotransporters display sodium- and phlorizin-dependent water permeability

The American Journal of Physiology
J LoikeJ Fischbarg

Abstract

Expression of Na(+)-glucose cotransporters of the SGLT-1 type by Xenopus laevis oocytes increased the osmotic water permeability (Pf) of oocytes by a factor of 1.9-2.8, in the presence and in the absence of 5 mM extracellular glucose. The Pf increase was correlated with the amount of SGLT-1 cRNA injected. In oocytes expressing SGLT-1, either addition of phlorizin to the medium or the replacement of Na+ by choline inhibited the uptake of methyl-alpha-D-glucopyranoside, a specific substrate for SGLT-1, and returned oocyte Pf to its level in uninjected oocytes. Phlorizin inhibited the SGLT-1-attributable increase in Pf with an inhibition constant (Ki) of 6.1 microM, a value analogous to the Ki for phlorizin inhibition of sugar uptake. However, neither the presence of phlorizin nor the absence of extracellular Na+ significantly affected the increase in Pf elicited in oocytes expressing GLUT-1, a facilitative glucose transporter. These findings suggest that SGLT-1 forms a pore that allows the transmembrane passage of water and that water and glucose traverse the protein through this pore. The finding that removal of extracellular Na+ abolishes the increase in Pf attributable to SGLT-1 suggests that extracellular Na+ is required to m...Continue Reading

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Citations

Nov 3, 2016·Proceedings of the National Academy of Sciences of the United States of America·Thomas ZeuthenDonald D F Loo
Jun 22, 1999·The Journal of Physiology·D D LooE M Wright
Jun 6, 1998·The Journal of Physiology·A MeinildT Zeuthen
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Jan 22, 2010·The Journal of Membrane Biology·Thomas Zeuthen
Apr 30, 2011·Physiological Reviews·Ernest M WrightBruce A Hirayama
Mar 6, 2016·The Journal of Biological Chemistry·Liudmila ErokhovaPeter Pohl
Jul 4, 2002·The Journal of Physiology·Donald D F LooThomas Zeuthen
Mar 17, 2001·The Journal of Physiology·T ZeuthenD A Klaerke
Oct 4, 2013·American Journal of Physiology. Renal Physiology·Zesergio MeloGerardo Gamba
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Oct 16, 1999·Biochimica Et Biophysica Acta·W Weber
Oct 19, 2011·Biophysical Journal·Louis J SassevilleSergei Y Noskov

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