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.
The relation between charge movement and transport-associated currents in the rat GABA cotransporter rGAT1.
Fesce R
,
Giovannardi S
,
Binda F
,
Bossi E
,
Peres A
.
???displayArticle.abstract???
Most cotransporters characteristically display two main kinds of electrical activity: in the absence of organic substrate, transient presteady-state currents (I(pre)) are generated by charge relocation during voltage steps; in the presence of substrate, sustained, transport-associated currents (I(tr)) are recorded. Quantitative comparison of these two currents, in Xenopus oocytes expressing the neural GABA cotransporter rGAT1, revealed several unforeseen consistencies between I(pre) and I(tr), in terms of magnitude and kinetic parameters. The decay rate constant (r) of I(pre) and the quantity of charge displaced to an inner position in the transporter (Q(in)(0)) depended on voltage and ionic conditions. Saturating GABA concentrations, applied under the same conditions, suppressed I(pre) (i.e. Q(in)( infinity ) = 0) and produced a transport-associated current with amplitude I(tr) = Q(in)(0)r. At non-saturating levels of GABA, changes of I(tr) were compensated by corresponding variations in Q(in), such that I(pre) and I(tr) complemented each other, according to the relation: I(tr) = (Q(in)(0) - Q(in)) r. Complementarity of magnitude, superimposable kinetic properties and equal dependence on voltage and [Na(+)](o) point to the uniqueness of the charge carrier for both processes, suggesting that transport and charge migration arise from the same molecular mechanism. The observed experimental relations were correctly predicted by a simple three-state kinetic model, in which GABA binding takes place after charge binding and inward migration have occurred. The model also predicts the observed voltage dependence of the apparent affinity of the transporter for GABA, and suggests a voltage-independent GABA binding rate with a value around 0.64 microM(-1) s(-1).
Armstrong,
Charge movement associated with the opening and closing of the activation gates of the Na channels.
1974, Pubmed
Armstrong,
Charge movement associated with the opening and closing of the activation gates of the Na channels.
1974,
Pubmed
Barish,
A transient calcium-dependent chloride current in the immature Xenopus oocyte.
1983,
Pubmed
,
Xenbase
Binda,
Temperature effects on the presteady-state and transport-associated currents of GABA cotransporter rGAT1.
2002,
Pubmed
Bossi,
Role of anion-cation interactions on the pre-steady-state currents of the rat Na(+)-Cl(-)-dependent GABA cotransporter rGAT1.
2002,
Pubmed
,
Xenbase
Bossi,
Ion binding and permeation through the lepidopteran amino acid transporter KAAT1 expressed in Xenopus oocytes.
1999,
Pubmed
,
Xenbase
Catterall,
Structure and function of voltage-gated ion channels.
1993,
Pubmed
DeFelice,
Single-file diffusion and neurotransmitter transporters: Hodgkin and Keynes model revisited.
2001,
Pubmed
DODGE,
Sodium currents in the myelinated nerve fibre of Xenopus laevis investigated with the voltage clamp technique.
1959,
Pubmed
,
Xenbase
Forlani,
Three kinds of currents in the canine betaine-GABA transporter BGT-1 expressed in Xenopus laevis oocytes.
2001,
Pubmed
,
Xenbase
Forlani,
Mutation K448E in the external loop 5 of rat GABA transporter rGAT1 induces pH sensitivity and alters substrate interactions.
2001,
Pubmed
,
Xenbase
Forster,
Proton-sensitive transitions of renal type II Na(+)-coupled phosphate cotransporter kinetics.
2000,
Pubmed
,
Xenbase
Hazama,
Presteady-state currents of the rabbit Na+/glucose cotransporter (SGLT1).
1997,
Pubmed
,
Xenbase
Hilgemann,
GAT1 (GABA:Na+:Cl-) cotransport function. Database reconstruction with an alternating access model.
1999,
Pubmed
,
Xenbase
HODGKIN,
The components of membrane conductance in the giant axon of Loligo.
1952,
Pubmed
Kusano,
Cholinergic and catecholaminergic receptors in the Xenopus oocyte membrane.
1982,
Pubmed
,
Xenbase
Lester,
Listening to neurotransmitter transporters.
1996,
Pubmed
Loo,
Conformational changes couple Na+ and glucose transport.
1998,
Pubmed
,
Xenbase
Lu,
GAT1 (GABA:Na+:Cl-) cotransport function. Kinetic studies in giant Xenopus oocyte membrane patches.
1999,
Pubmed
,
Xenbase
Lu,
GAT1 (GABA:Na+:Cl-) cotransport function. Steady state studies in giant Xenopus oocyte membrane patches.
1999,
Pubmed
,
Xenbase
Mager,
Steady states, charge movements, and rates for a cloned GABA transporter expressed in Xenopus oocytes.
1993,
Pubmed
,
Xenbase
Mager,
Ion binding and permeation at the GABA transporter GAT1.
1996,
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
Su,
A multi-substrate single-file model for ion-coupled transporters.
1996,
Pubmed
