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.

Cl- effects on the function of the GABA cotransporter rGAT1 preserve the mutual relation between transient and transport currents

FESCE R.;
2003

Abstract

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.
XENOPUS-LAEVIS OOCYTES; AMINO-ACID TRANSPORTER; GABA TRANSPORTER; MEMBRANE-PROTEINS; TOPOLOGY PREDICTION; ION-BINDING; RAT-BRAIN; NA+ COTRANSPORTER; SODIUM AND CHLORIDE DEPENDENCE
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11699/5993
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