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The actual ionic nature of the leak current through the Na+/glucose cotransporter SGLT1.
- Source :
-
Biophysical journal [Biophys J] 2010 Jan 20; Vol. 98 (2), pp. 231-9. - Publication Year :
- 2010
-
Abstract
- Expression of the Na(+)/glucose cotransporter SGLT1 in Xenopus oocytes is characterized by a phlorizin-sensitive leak current (in the absence of glucose) that was originally called a "Na(+) leak" and represents some 5-10% of the maximal Na(+)/glucose cotransport current. We analyzed the ionic nature of the leak current using a human SGLT1 mutant (C292A) displaying a threefold larger leak current while keeping a reversal potential (V(R)) of approximately -15 mV as observed for wt SGLT1. V(R) showed only a modest negative shift when extracellular Na(+) concentration ([Na(+)](o)) was lowered and it was completely insensitive to changes in extracellular Cl(-). When extracellular pH (pH(o)) was decreased from 7.5 to 6.5 and 5.5, V(R) shifted by +15 and +40 mV, respectively, indicating that protons may be the main charge carrier at low pH(o) but other ions must be involved at pH(o) 7.5. In the presence of 15 mM [Na(+)](o) (pH(o) = 7.5), addition of 75 mM of either Na(+), Li(+), Cs(+), or K(+) generated similar increases in the leak current amplitude. This observation, which was confirmed with wt SGLT1, indicates a separate pathway for the leak current with respect to the cotransport current. This means that, contrary to previous beliefs, the leak current cannot be accounted for by the translocation of the Na-loaded and glucose-free cotransporter. Using chemical modification and different SGLT1 mutants, a relationship was found between the cationic leak current and the passive water permeability suggesting that water and cations may share a common pathway through the cotransporter.<br /> (Copyright 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.)
- Subjects :
- Animals
Cesium chemistry
Chlorides chemistry
Dithiothreitol chemistry
Extracellular Space chemistry
Humans
Hydrogen-Ion Concentration
Lithium chemistry
Membrane Potentials
Mutation, Missense
Patch-Clamp Techniques
Potassium chemistry
Reducing Agents chemistry
Sodium chemistry
Sodium-Glucose Transporter 1 genetics
Water chemistry
Xenopus laevis
Ions chemistry
Sodium-Glucose Transporter 1 chemistry
Subjects
Details
- Language :
- English
- ISSN :
- 1542-0086
- Volume :
- 98
- Issue :
- 2
- Database :
- MEDLINE
- Journal :
- Biophysical journal
- Publication Type :
- Academic Journal
- Accession number :
- 20338844
- Full Text :
- https://doi.org/10.1016/j.bpj.2009.10.015