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 sodium/myo-inositol transporter 2 (SMIT2) is a member of the SLC5A gene family, which is believed to share the five-transmembrane segment inverted repeat of the LeuT structural family. The two-electrode voltage-clamp (TEVC) technique was used to measure the steady-state and the pre-steady-state currents mediated by human SMIT2 after expression in Xenopus laevis oocytes. Phlorizin is first shown to be a poor inhibitor of pre-steady-state currents for depolarizing voltage pulse. From an up to threefold difference between the apparent ON and OFF transferred charges during a voltage pulse, we also show that a fraction of the transient current recorded for very negative potentials is not a true pre-steady-state current coming from the cotransporter conformational changes. We suggest that this transient current comes from a time-dependent leak current that can reach large amplitudes when external Na(+) concentration is reduced. A kinetic model was generated through a simulated annealing algorithm. This algorithm was used to identify the optimal connectivity among 19 different kinetic models and obtain the numerical values of the associated parameters. The proposed 5-state model includes cooperative binding of Na(+) ions, strong apparent asymmetry of the energy barriers, a rate-limiting step that is likely associated with the translocation of the empty transporter, and a turnover rate of 21 s(-1). The proposed model is a proof of concept for a novel approach to kinetic modeling of electrogenic transporters and allows insight into the transport mechanism of members of the LeuT structural family at the millisecond timescale.
Aouameur,
SMIT2 mediates all myo-inositol uptake in apical membranes of rat small intestine.
2007, Pubmed,
Xenbase
Aouameur,
SMIT2 mediates all myo-inositol uptake in apical membranes of rat small intestine.
2007,
Pubmed
,
Xenbase Bissonnette,
Expression of the sodium-myo-inositol cotransporter SMIT2 at the apical membrane of Madin-Darby canine kidney cells.
2004,
Pubmed
,
Xenbase Bourgeois,
Determination of transport stoichiometry for two cation-coupled myo-inositol cotransporters: SMIT2 and HMIT.
2005,
Pubmed
,
Xenbase Chanda,
Gating charge displacement in voltage-gated ion channels involves limited transmembrane movement.
2005,
Pubmed Chen,
Fast voltage clamp discloses a new component of presteady-state currents from the Na(+)-glucose cotransporter.
1996,
Pubmed
,
Xenbase Chen,
Thermodynamic determination of the Na+: glucose coupling ratio for the human SGLT1 cotransporter.
1995,
Pubmed
,
Xenbase Chen,
Sodium leak pathway and substrate binding order in the Na+-glucose cotransporter.
1997,
Pubmed
,
Xenbase Coady,
Identification of a novel Na+/myo-inositol cotransporter.
2002,
Pubmed
,
Xenbase Coady,
Establishing a definitive stoichiometry for the Na+/monocarboxylate cotransporter SMCT1.
2007,
Pubmed Ehrenkranz,
Phlorizin: a review.
2005,
Pubmed Eskandari,
Thyroid Na+/I- symporter. Mechanism, stoichiometry, and specificity.
1997,
Pubmed
,
Xenbase Eskandari,
Kinetics of the reverse mode of the Na+/glucose cotransporter.
2005,
Pubmed
,
Xenbase Faham,
The crystal structure of a sodium galactose transporter reveals mechanistic insights into Na+/sugar symport.
2008,
Pubmed Fang,
Structure of a prokaryotic virtual proton pump at 3.2 A resolution.
2009,
Pubmed Gagnon,
Effect of substrate on the pre-steady-state kinetics of the Na(+)/glucose cotransporter.
2007,
Pubmed
,
Xenbase Gao,
Structure and mechanism of an amino acid antiporter.
2009,
Pubmed Guy,
Molecular model of the action potential sodium channel.
1986,
Pubmed Hager,
Kinetics and specificity of the renal Na+/myo-inositol cotransporter expressed in Xenopus oocytes.
1995,
Pubmed
,
Xenbase Hirayama,
Protons drive sugar transport through the Na+/glucose cotransporter (SGLT1).
1994,
Pubmed
,
Xenbase Kahlig,
Amphetamine induces dopamine efflux through a dopamine transporter channel.
2005,
Pubmed Krishnamurthy,
Unlocking the molecular secrets of sodium-coupled transporters.
2009,
Pubmed Lahjouji,
Expression and functionality of the Na+/myo-inositol cotransporter SMIT2 in rabbit kidney.
2007,
Pubmed Longpré,
Simulated annealing reveals the kinetic activity of SGLT1, a member of the LeuT structural family.
2012,
Pubmed
,
Xenbase Longpré,
The actual ionic nature of the leak current through the Na+/glucose cotransporter SGLT1.
2010,
Pubmed
,
Xenbase Loo,
How drugs interact with transporters: SGLT1 as a model.
2008,
Pubmed
,
Xenbase Loo,
Conformational dynamics of hSGLT1 during Na+/glucose cotransport.
2006,
Pubmed
,
Xenbase Ma,
Structure and mechanism of a glutamate-GABA antiporter.
2012,
Pubmed MacAulay,
Water transport between CNS compartments: contributions of aquaporins and cotransporters.
2010,
Pubmed Parent,
Electrogenic properties of the cloned Na+/glucose cotransporter: II. A transport model under nonrapid equilibrium conditions.
1992,
Pubmed Ressl,
Molecular basis of transport and regulation in the Na(+)/betaine symporter BetP.
2009,
Pubmed Santacroce,
Passive water permeability of some wild type and mutagenized amino acid cotransporters of the SLC6/NSS family expressed in Xenopus laevis oocytes.
2010,
Pubmed
,
Xenbase Sasseville,
The structural pathway for water permeation through sodium-glucose cotransporters.
2011,
Pubmed
,
Xenbase Schicker,
Unifying concept of serotonin transporter-associated currents.
2012,
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 Shaffer,
Structure and mechanism of a Na+-independent amino acid transporter.
2009,
Pubmed Silbernagl,
Tubular reabsorption of myo-inositol vs. that of D-glucose in rat kidney in vivo et situ.
2003,
Pubmed Tang,
Crystal structure of the carnitine transporter and insights into the antiport mechanism.
2010,
Pubmed Weyand,
Structure and molecular mechanism of a nucleobase-cation-symport-1 family transporter.
2008,
Pubmed Yamashita,
Crystal structure of a bacterial homologue of Na+/Cl--dependent neurotransmitter transporters.
2005,
Pubmed
