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.
J Membr Biol
2005 Mar 01;2041:23-32. doi: 10.1007/s00232-005-0743-x.
Show Gene links
Show Anatomy links
Kinetics of the reverse mode of the Na+/glucose cotransporter.
Eskandari S
,
Wright EM
,
Loo DD
.
???displayArticle.abstract???
This study investigates the reverse mode of the Na(+)/glucose cotransporter (SGLT1). In giant excised inside-out membrane patches from Xenopus laevis oocytes expressing rabbit SGLT1, application of alpha-methyl-D: -glucopyranoside (alphaMDG) to the cytoplasmic solution induced an outward current from cytosolic to external membrane surface. The outward current was Na(+)- and sugar-dependent, and was blocked by phlorizin, a specific inhibitor of SGLT1. The current-voltage relationship saturated at positive membrane voltages (30-50 mV), and approached zero at -150 mV. The half-maximal concentration for alphaMDG-evoked outward current (K(0.5) (alphaMDG)) was 35 mM (at 0 mV). In comparison, K(0.5) (alphaMDG) for forward sugar transport was 0.15 mM (at 0 mV). K(0.5) (Na) was similar for forward and reverse transport ( approximately 35 mM at 0 mV). Specificity of SGLT1 for reverse transport was: alphaMDG (1.0) > D: -galactose (0.84) > 3-O-methyl-glucose (0.55) > D: -glucose (0.38), whereas for forward transport, specificity was: alphaMDG approximately D: -glucose approximately D: -galactose > 3-O-methyl-glucose. Thus there is an asymmetry in sugar kinetics and specificity between forward and reverse modes. Computer simulations showed that a 6-state kinetic model for SGLT1 can account for Na(+)/sugar cotransport and its voltage dependence in both the forward and reverse modes at saturating sodium concentrations. Our data indicate that under physiological conditions, the transporter is poised to accumulate sugar efficiently in the enterocyte.
Abramson,
Structure and mechanism of the lactose permease of Escherichia coli.
2003, Pubmed
Abramson,
Structure and mechanism of the lactose permease of Escherichia coli.
2003,
Pubmed
Birnir,
Voltage-clamp studies of the Na+/glucose cotransporter cloned from rabbit small intestine.
1991,
Pubmed
,
Xenbase
Chen,
Thermodynamic determination of the Na+: glucose coupling ratio for the human SGLT1 cotransporter.
1995,
Pubmed
,
Xenbase
Díez-Sampedro,
Residue 457 controls sugar binding and transport in the Na(+)/glucose cotransporter.
2001,
Pubmed
,
Xenbase
Falk,
Reduction of an eight-state mechanism of cotransport to a six-state model using a new computer program.
1998,
Pubmed
Firnges,
Functional asymmetry of the sodium-D-glucose cotransporter expressed in yeast secretory vesicles.
2001,
Pubmed
Guan,
Binding affinity of lactose permease is not altered by the H+ electrochemical gradient.
2004,
Pubmed
Hazama,
Presteady-state currents of the rabbit Na+/glucose cotransporter (SGLT1).
1997,
Pubmed
,
Xenbase
Hediger,
Expression cloning and cDNA sequencing of the Na+/glucose co-transporter.
,
Pubmed
,
Xenbase
Hirayama,
Kinetic and specificity differences between rat, human, and rabbit Na+-glucose cotransporters (SGLT-1).
1996,
Pubmed
,
Xenbase
Hirayama,
Cation effects on protein conformation and transport in the Na+/glucose cotransporter.
1997,
Pubmed
,
Xenbase
Ikeda,
Characterization of a Na+/glucose cotransporter cloned from rabbit small intestine.
1989,
Pubmed
,
Xenbase
Kaunitz,
Kinetics of sodium D-glucose cotransport in bovine intestinal brush border vesicles.
1984,
Pubmed
Kessler,
The small-intestinal Na+, D-glucose cotransporter: an asymmetric gated channel (or pore) responsive to delta psi.
1983,
Pubmed
Loo,
Relaxation kinetics of the Na+/glucose cotransporter.
1993,
Pubmed
,
Xenbase
Loo,
Conformational changes couple Na+ and glucose transport.
1998,
Pubmed
,
Xenbase
Mackenzie,
Relationships between Na+/glucose cotransporter (SGLT1) currents and fluxes.
1998,
Pubmed
,
Xenbase
Meinild,
Fluorescence studies of ligand-induced conformational changes of the Na(+)/glucose cotransporter.
2002,
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,
Functional asymmetry of the human Na+/glucose transporter (hSGLT1) in bacterial membrane vesicles.
2003,
Pubmed
Sauer,
Voltage and substrate dependence of the inverse transport mode of the rabbit Na(+)/glucose cotransporter (SGLT1).
2000,
Pubmed
,
Xenbase
Umbach,
Intestinal Na+/glucose cotransporter expressed in Xenopus oocytes is electrogenic.
1990,
Pubmed
,
Xenbase
Wang,
Syntaxin 1A inhibits GABA flux, efflux, and exchange mediated by the rat brain GABA transporter GAT1.
2003,
Pubmed
,
Xenbase
