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.
???displayArticle.abstract???
The Na+-glucose cotransporter (SGLT1) expressed in Xenopus laevis oocytes was shown to generate a phlorizin-sensitive sodium leak in the absence of sugars. Using the current model for SGLT1, where the sodium leak was presumed to occur after two sodium ions are bound to the free carrier before glucose binding, a characteristic concentration constant (Kc) was introduced to describe the relative importance of the sodium leak versus Na+-glucose cotransport currents. Kc represents the glucose concentration at which the Na+-glucose cotransport current is equal to the sodium leak. As both the sodium leak and the Na+-glucose cotransport current are predicted to occur after the binding of two sodium ions, the model predicted that Kc should be sodium-independent. However, by using a two-microelectrode voltage-clamp technique, the observed Kc was shown to depend strongly on the external sodium concentration ([Na+]o): it was four times higher at 5 mM [Na+]o than at 20 mM [Na+]o. In addition, the magnitude of the sodium leak varied as a function of [Na+]o in a Michaelian fashion, and the sodium affinity constant for the sodium leak was 2-4 times lower than that for cotransport in the presence of low external glucose concentrations (50 or 100 microM), whereas the current model predicted a sigmoidal sodium dependence of the sodium leak and identical sodium affinities for the sodium leak and the Na+-glucose cotransport. These observations indicate that the sodium leak occurs after one sodium ion is associated with the carrier and agree with predictions from a model with the binding order sodium-glucose-sodium. This conclusion was also supported by experiments performed where protons replaced Na+ as a "driving cation."
Aronson,
Energy-dependence of phlorizin binding to isolated renal microvillus membranes. Evidence concerning the mechanism of coupling between the electrochemical Na+ gradient the sugar transport.
1978, Pubmed
Aronson,
Energy-dependence of phlorizin binding to isolated renal microvillus membranes. Evidence concerning the mechanism of coupling between the electrochemical Na+ gradient the sugar transport.
1978,
Pubmed Bennett,
Na+ binding to the Na(+)-glucose cotransporter is potential dependent.
1992,
Pubmed Bennett,
The molecular mechanism and potential dependence of the Na+/glucose cotransporter.
1996,
Pubmed Chen,
Thermodynamic determination of the Na+: glucose coupling ratio for the human SGLT1 cotransporter.
1995,
Pubmed
,
Xenbase Chen,
Fast voltage clamp discloses a new component of presteady-state currents from the Na(+)-glucose cotransporter.
1996,
Pubmed
,
Xenbase Chenu,
Allosterism and Na(+)-D-glucose cotransport kinetics in rabbit jejunal vesicles: compatibility with mixed positive and negative cooperativities in a homo- dimeric or tetrameric structure and experimental evidence for only one transport protein involved.
1993,
Pubmed Coady,
Sequence homologies among intestinal and renal Na+/glucose cotransporters.
1990,
Pubmed Crane,
The gradient hypothesis and other models of carrier-mediated active transport.
1977,
Pubmed Hediger,
Expression cloning and cDNA sequencing of the Na+/glucose co-transporter.
,
Pubmed
,
Xenbase Hediger,
Homology of the human intestinal Na+/glucose and Escherichia coli Na+/proline cotransporters.
1989,
Pubmed Hirayama,
Protons drive sugar transport through the Na+/glucose cotransporter (SGLT1).
1994,
Pubmed
,
Xenbase Kessler,
The small-intestinal Na+, D-glucose cotransporter: an asymmetric gated channel (or pore) responsive to delta psi.
1983,
Pubmed Kimmich,
Membrane potentials and the mechanism of intestinal Na(+)-dependent sugar transport.
1990,
Pubmed Kimmich,
Na+-coupled sugar transport: membrane potential-dependent Km and Ki for Na+.
1988,
Pubmed Koepsell,
Two substrate sites in the renal Na(+)-D-glucose cotransporter studied by model analysis of phlorizin binding and D-glucose transport measurements.
1990,
Pubmed Lee,
The high affinity Na+/glucose cotransporter. Re-evaluation of function and distribution of expression.
1994,
Pubmed
,
Xenbase Loo,
Relaxation kinetics of the Na+/glucose cotransporter.
1993,
Pubmed
,
Xenbase Lostao,
Phenylglucosides and the Na+/glucose cotransporter (SGLT1): analysis of interactions.
1994,
Pubmed
,
Xenbase Mackenzie,
SAAT1 is a low affinity Na+/glucose cotransporter and not an amino acid transporter. A reinterpretation.
1994,
Pubmed
,
Xenbase Moran,
High affinity phlorizin binding to the LLC-PK1 cells exhibits a sodium:phlorizin stoichiometry of 2:1.
1988,
Pubmed Ohta,
Regulation of glucose transporters in LLC-PK1 cells: effects of D-glucose and monosaccharides.
1990,
Pubmed Panayotova-Heiermann,
Sugar binding to Na+/glucose cotransporters is determined by the carboxyl-terminal half of the protein.
1996,
Pubmed
,
Xenbase Panayotova-Heiermann,
Kinetics of steady-state currents and charge movements associated with the rat Na+/glucose cotransporter.
1995,
Pubmed
,
Xenbase Parent,
Electrogenic properties of the cloned Na+/glucose cotransporter: II. A transport model under nonrapid equilibrium conditions.
1992,
Pubmed Parent,
Electrogenic properties of the cloned Na+/glucose cotransporter: I. Voltage-clamp studies.
1992,
Pubmed
,
Xenbase Quick,
Incubation with horse serum increases viability and decreases background neurotransmitter uptake in Xenopus oocytes.
1992,
Pubmed
,
Xenbase Restrepo,
Phlorizin binding to isolated enterocytes: membrane potential and sodium dependence.
1986,
Pubmed Restrepo,
Kinetic analysis of mechanism of intestinal Na+-dependent sugar transport.
1985,
Pubmed RIKLIS,
Effects of cations on sugar absorption by isolated surviving guinea pig intestine.
1958,
Pubmed Schultz,
Coupled transport of sodium and organic solutes.
1970,
Pubmed Semenza,
Biochemistry of the Na+, D-glucose cotransporter of the small-intestinal brush-border membrane. The state of the art in 1984.
1984,
Pubmed Tannenbaum,
High-affinity phlorizin binding to brush border membranes from small intestine: identity with (a part of) the glucose transport system, dependence on Na +-gradient, partial purification.
1977,
Pubmed Tarpey,
Molecular characterisation of the Na+/glucose co-transporter from the sheep parotid gland acinar cell.
1994,
Pubmed Toggenburger,
Phlorizin as a probe of the small-intestinal Na+,D-glucose cotransporter. A model.
1982,
Pubmed Turner,
Further studies of proximal tubular brush border membrane D-glucose transport heterogeneity.
1982,
Pubmed Turner,
Stoichiometric studies of the renal outer cortical brush border membrane D-glucose transporter.
1982,
Pubmed Umbach,
Intestinal Na+/glucose cotransporter expressed in Xenopus oocytes is electrogenic.
1990,
Pubmed
,
Xenbase Veyhl,
Cloning of a membrane-associated protein which modifies activity and properties of the Na(+)-D-glucose cotransporter.
1993,
Pubmed
,
Xenbase Wells,
Cloning of a human kidney cDNA with similarity to the sodium-glucose cotransporter.
1992,
Pubmed
,
Xenbase Wright,
The intestinal Na+/glucose cotransporter.
1993,
Pubmed
