Affiliation:
1. Laboratory of Cellular and Molecular Physiology, Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy; and
2. Fondazione Maugeri Istituto di Ricovero e Cura a Carattere Scientifico, Tradate, Italy
Abstract
The role of internal substrates in the biophysical properties of the GABA transporter GAT1 has been investigated electrophysiologically in Xenopus oocytes heterologously expressing the cotransporter. Increments in Cl− and/or Na+ concentrations caused by intracellular injections did not produce significant effects on the pre-steady-state currents, while a positive shift of the charge-voltage ( Q–V) and decay time constant (τ)-voltage (τ- V) curves, together with a slowing of τ at positive potentials, was observed following treatments producing cytosolic Cl− depletion. Activation of the reverse transport mode by injections of GABA caused a reduction in the displaced charge. In the absence of external Cl−, a stronger reduction in the displaced charge, together with a significant increase in reverse transport current, was observed. Therefore, complementarity between pre-steady-state and transport currents, observed in the forward mode, is preserved in the reverse mode. All these findings can be qualitatively reproduced by a kinetic scheme in which, in the forward mode, the Cl− ion is released first, after the inward charge movement, while the two Na+ ions can be released only after binding of external GABA. In the reverse mode, internal GABA must bind first to the empty transporter, followed by internal Na+ and Cl−.
Publisher
American Physiological Society
Cited by
11 articles.
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