Cl- affects the function of the GABA cotransporter rGAT1 but preserves the mutal relationship between transient and transport currents.
The effects of reducing external Cl- on the electrophysiological properties of the Na+/Cl(-)-dependent GABA transporter rGAT1 expressed in Xenopus oocytes were investigated. In agreement with a recently proposed kinetic scheme, the effects of Cl- are complex but preserve the mutual relationship that links the transport-associated current, I(tr), measured in saturating GABA concentration, and the transient current, I(pre), recorded in the absence of GABA following a voltage step from the holding potential Vh to V. In particular, I(tr) (V) - I(tr) (Vh) = r integral I(pre) (V) dt, where r is the relaxation rate of I(pre) at the same membrane potential and Cl- concentration. The model also predicts a relationship between charge relaxation rate and apparent affinity for GABA, which is also verified in the presence of lowered Na+ or Cl- concentrations. In these conditions, the binding rate of GABA to the transporter is increased. All these effects are consistent with the hypothesis that interaction of the organic substrate with rGAT1 induces a conversion from a capacitive to a conductive mode of operation without strongly altering either the amount or the rate of charge movement.
Giovannardi
S
S
Laboratory of Cellular and Molecular Physiology, Department of Structural and Functional Biology, University of Insubria, Via Dunant 3, 21100 Varese, Italy.
Fesce
R
R
Bossi
E
E
Binda
F
F
Peres
A
A
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002713:Chlorine / Q000378:metabolism*; D005260:Female; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009865:Oocytes / Q000378:metabolism; D027361:Organic Anion Transporters; D012964:Sodium / Q000378:metabolism; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; C493415:Slc6a1 protein, rat; D002713:Chlorine; D005680:gamma-Aminobutyric Acid; D012964:Sodium