Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
Glucose accumulation can account for the initial water flux triggered by Na+/glucose cotransport.
Gagnon MP
,
Bissonnette P
,
Deslandes LM
,
Wallendorff B
,
Lapointe JY
.
???displayArticle.abstract???
Over the last decade, several cotransport studies have led to the proposal of secondary active transport of water, challenging the dogma that all water transport is passive. The major observation leading to this interpretation was that a Na+ influx failed to reproduce the large and rapid cell swelling induced by Na+/solute cotransport. We have investigated this phenomenon by comparing a Na+/glucose (hSGLT1) induced water flux to water fluxes triggered either by a cationic inward current (using ROMK2 K+ channels) or by a glucose influx (using GLUT2, a passive glucose transporter). These proteins were overexpressed in Xenopus oocytes and assayed through volumetric measurements combined with double-electrode electrophysiology or radioactive uptake measurements. The osmotic gradients driving the observed water fluxes were estimated by comparison with the swelling induced by osmotic shocks of known amplitude. We found that, for equivalent cation or glucose uptakes, the combination of substrate accumulations observed with ROMK2 and GLUT2 are sufficient to provide the osmotic gradient necessary to account for a passive water flux through SGLT1. Despite the fact that the Na+/glucose stoichiometry of SGLT1 is 2:1, glucose accumulation accounts for two-thirds of the osmotic gradient responsible for the water flux observed at t = 30 s. It is concluded that the different accumulation processes for neutral versus charged solutes can quantitatively account for the fast water flux associated with Na+/glucose cotransport activation without having to propose the presence of secondary active water transport.
Bissonnette,
Functional expression of tagged human Na+-glucose cotransporter in Xenopus laevis oocytes.
1999, Pubmed,
Xenbase
Bissonnette,
Functional expression of tagged human Na+-glucose cotransporter in Xenopus laevis oocytes.
1999,
Pubmed
,
Xenbase
Coady,
Identification of a novel Na+/myo-inositol cotransporter.
2002,
Pubmed
,
Xenbase
Colville,
Kinetic analysis of the liver-type (GLUT2) and brain-type (GLUT3) glucose transporters in Xenopus oocytes: substrate specificities and effects of transport inhibitors.
1993,
Pubmed
,
Xenbase
Cougnon,
Further investigation of ionic diffusive properties and of NH4+ pathways in Xenopus laevis oocyte cell membrane.
1996,
Pubmed
,
Xenbase
Duquette,
Local osmotic gradients drive the water flux associated with Na(+)/glucose cotransport.
2001,
Pubmed
,
Xenbase
Fischbarg,
Evidence that the glucose transporter serves as a water channel in J774 macrophages.
1989,
Pubmed
Fischbarg,
Glucose transporters serve as water channels.
1990,
Pubmed
,
Xenbase
Gould,
Expression of human glucose transporters in Xenopus oocytes: kinetic characterization and substrate specificities of the erythrocyte, liver, and brain isoforms.
1991,
Pubmed
,
Xenbase
Hu,
The abnormality of glucose transporter in the erythrocyte membrane of Chinese type 2 diabetic patients.
2000,
Pubmed
Iserovich,
Changes in glucose transport and water permeability resulting from the T310I pathogenic mutation in Glut1 are consistent with two transport channels per monomer.
2002,
Pubmed
,
Xenbase
Lapointe,
The presence of local osmotic gradients can account for the water flux driven by the Na+-glucose cotransporter.
2002,
Pubmed
Lapointe,
Controversy regarding the secondary active water transport hypothesis.
2002,
Pubmed
,
Xenbase
Loo,
Cotransport of water by the Na+/glucose cotransporter.
1996,
Pubmed
,
Xenbase
Ma,
Aquaporin water channels in gastrointestinal physiology.
1999,
Pubmed
MacAulay,
Water transport by the human Na+-coupled glutamate cotransporter expressed in Xenopus oocytes.
2001,
Pubmed
,
Xenbase
Macey,
Transport of water and urea in red blood cells.
1984,
Pubmed
Meinild,
The human Na+-glucose cotransporter is a molecular water pump.
1998,
Pubmed
,
Xenbase
Meinild,
Water transport by the renal Na(+)-dicarboxylate cotransporter.
2000,
Pubmed
,
Xenbase
Preston,
Isolation of the cDNA for erythrocyte integral membrane protein of 28 kilodaltons: member of an ancient channel family.
1991,
Pubmed
Schreibmayer,
Voltage clamping of Xenopus laevis oocytes utilizing agarose-cushion electrodes.
1994,
Pubmed
,
Xenbase
Wright,
Coupling between Na+, sugar, and water transport across the intestine.
2000,
Pubmed
Zampighi,
A method for determining the unitary functional capacity of cloned channels and transporters expressed in Xenopus laevis oocytes.
1995,
Pubmed
,
Xenbase
Zeidel,
Role of glucose carrier in human erythrocyte water permeability.
1992,
Pubmed
Zeuthen,
Secondary active transport of water across ventricular cell membrane of choroid plexus epithelium of Necturus maculosus.
1991,
Pubmed
Zeuthen,
Cotransport of K+, Cl- and H2O by membrane proteins from choroid plexus epithelium of Necturus maculosus.
1994,
Pubmed
Zeuthen,
Water transport by the Na+/glucose cotransporter under isotonic conditions.
1997,
Pubmed
,
Xenbase
Zeuthen,
Isotonic transport by the Na+-glucose cotransporter SGLT1 from humans and rabbit.
2001,
Pubmed
,
Xenbase
Zeuthen,
Mobility of ions, sugar, and water in the cytoplasm of Xenopus oocytes expressing Na(+)-coupled sugar transporters (SGLT1).
2002,
Pubmed
,
Xenbase
Zhang,
Cloning, functional analysis and cell localization of a kidney proximal tubule water transporter homologous to CHIP28.
1993,
Pubmed
,
Xenbase
