Conformational basis for the Li(+)-induced leak current in the rat gamma-aminobutyric acid (GABA) transporter-1
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Conformational basis for the Li(+)-induced leak current in the rat gamma-aminobutyric acid (GABA) transporter-1. / MacAulay, Nanna; Zeuthen, Thomas; Gether, Ulrik.
In: Journal of Physiology, Vol. 544, No. Pt 2, 15.10.2002, p. 447-58.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Conformational basis for the Li(+)-induced leak current in the rat gamma-aminobutyric acid (GABA) transporter-1
AU - MacAulay, Nanna
AU - Zeuthen, Thomas
AU - Gether, Ulrik
PY - 2002/10/15
Y1 - 2002/10/15
N2 - The rat gamma-aminobutyric acid transporter-1 (GAT-1) was expressed in Xenopus laevis oocytes and the substrate-independent Li(+)-induced leak current was examined using two-electrode voltage clamp. The leak current was not affected by the addition of GABA and was not due to H(+) permeation. The Li(+)-bound conformation of the protein displayed a lower passive water permeability than that of the Na(+)- and choline (Ch(+))-bound conformations and the leak current did not saturate with increasing amounts of Li(+) in the test solution. The mechanism that gives rise to the leak current did not support active water transport in contrast to the mechanism responsible for GABA translocation (approximately 330 water molecules per charge). Altogether, these data support the distinct nature of the leak conductance in relation to the substrate translocation process. It was observed that the leak current was inhibited by low millimolar concentrations of Na(+) (the apparent affinity constant, K'(0.5) = 3 mM). In addition, it was found that the GABA transport current was sustained at correspondingly low Na(+) concentrations if Li(+) was present instead of choline. This is consistent with a model in which Li(+) can bind and substitute for Na(+) at the putative "first" apparently low-affinity Na(+) binding site. In the absence of Na(+), this allows a Li(+)-permeable channel to open at hyperpolarized potentials. Occupancy of the "second" apparently high-affinity Na(+) binding site by addition of low millimolar concentrations of Na(+) restrains the transporter from moving into a leak conductance mode as well as allowing maintenance of GABA-elicited transport-associated current.
AB - The rat gamma-aminobutyric acid transporter-1 (GAT-1) was expressed in Xenopus laevis oocytes and the substrate-independent Li(+)-induced leak current was examined using two-electrode voltage clamp. The leak current was not affected by the addition of GABA and was not due to H(+) permeation. The Li(+)-bound conformation of the protein displayed a lower passive water permeability than that of the Na(+)- and choline (Ch(+))-bound conformations and the leak current did not saturate with increasing amounts of Li(+) in the test solution. The mechanism that gives rise to the leak current did not support active water transport in contrast to the mechanism responsible for GABA translocation (approximately 330 water molecules per charge). Altogether, these data support the distinct nature of the leak conductance in relation to the substrate translocation process. It was observed that the leak current was inhibited by low millimolar concentrations of Na(+) (the apparent affinity constant, K'(0.5) = 3 mM). In addition, it was found that the GABA transport current was sustained at correspondingly low Na(+) concentrations if Li(+) was present instead of choline. This is consistent with a model in which Li(+) can bind and substitute for Na(+) at the putative "first" apparently low-affinity Na(+) binding site. In the absence of Na(+), this allows a Li(+)-permeable channel to open at hyperpolarized potentials. Occupancy of the "second" apparently high-affinity Na(+) binding site by addition of low millimolar concentrations of Na(+) restrains the transporter from moving into a leak conductance mode as well as allowing maintenance of GABA-elicited transport-associated current.
KW - Animals
KW - Biological Transport
KW - Carrier Proteins
KW - Electric Conductivity
KW - Female
KW - GABA Plasma Membrane Transport Proteins
KW - Hydrogen-Ion Concentration
KW - Lithium
KW - Membrane Proteins
KW - Membrane Transport Proteins
KW - Molecular Conformation
KW - Oocytes
KW - Organic Anion Transporters
KW - Patch-Clamp Techniques
KW - Permeability
KW - Rats
KW - Sodium
KW - Water
KW - Xenopus laevis
M3 - Journal article
C2 - 12381817
VL - 544
SP - 447
EP - 458
JO - The Journal of Physiology
JF - The Journal of Physiology
SN - 0022-3751
IS - Pt 2
ER -
ID: 47293533