The relation between charge movement and transport‐associated currents in the rat GABA cotransporter rGAT1

Autor: Riccardo Fesce, F Binda, Stefano Giovannardi, Antonio Peres, Elena Bossi
Rok vydání: 2002
Předmět:
EXPRESSION
GABA Plasma Membrane Transport Proteins
Physiology
Voltage clamp
Kinetics
Xenopus
Analytical chemistry
Organic Anion Transporters
TRANSIENT
Kinetic energy
Models
Biological
CLONING
Xenopus laevis
Reaction rate constant
COUPLED COTRANSPORTERS
Animals
ELECTROGENIC PROPERTIES
XENOPUS OOCYTES
VOLTAGE-CLAMP
CLONING
EXPRESSION
KINETICS
AMINOBUTYRIC-ACID TRANSPORTER
PRE STEADY-STATE CURRENTS
COUPLED COTRANSPORTERS
GAT1
TRANSIENT
MODEL
EXPRESSION
gamma-Aminobutyric Acid
KINETICS
ELECTROGENIC PROPERTIES
biology
XENOPUS OOCYTES
Chemistry
Osmolar Concentration
Electric Conductivity
Membrane Proteins
Membrane Transport Proteins
PRE STEADY-STATE CURRENTS
Biological Transport
Original Articles
biology.organism_classification
Rats
MODEL
VOLTAGE-CLAMP
Amplitude
GAT1
Oocytes
Biophysics
AMINOBUTYRIC-ACID TRANSPORTER
Female
Charge carrier
Carrier Proteins
Cotransporter
Zdroj: The Journal of Physiology. 545:739-750
ISSN: 1469-7793
0022-3751
DOI: 10.1113/jphysiol.2002.026823
Popis: 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).
Databáze: OpenAIRE
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