Journal
CELLULAR AND MOLECULAR LIFE SCIENCES
Volume 60, Issue 3, Pages 550-556Publisher
BIRKHAUSER VERLAG AG
DOI: 10.1007/s000180300046
Keywords
cotransporter; GABA; Cl-; charge movement
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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 V-h to V In particular, I-tr (V)-I-tr (V-h) = 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.
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