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  • Title: Dual role of K+ and Na+ on the transport of [3H]-gamma-aminobutyric acid by synaptic plasma membrane vesicles.
    Author: Gonçalves PP, Carvalho AP.
    Journal: Brain Res Mol Brain Res; 1995 Aug; 32(1):161-5. PubMed ID: 7494456.
    Abstract:
    The influence of the monovalent cations (Na+ and K+) and of the electrical gradient on the high-affinity [3H]-gamma-aminobutyric acid ([3H]GABA) transport was investigated in synaptic plasma membrane (SPM) vesicles isolated from sheep brain cortex. This process specifically requires internal K+, since when it is replaced by Li+, the delta psi remains of the same order of magnitude, but no uptake of [3H]GABA occurs. The influence of the external Na+ concentration on the rate of [3H]GABA uptake suggests that this mechanism exhibits two components, whose characteristics are determined by the delta psi. Depolarization reduces the Jmax of [3H]GABA influx and enhances the binding of Na+ associated to [3H]GABA transport. Nevertheless, depolarization does not affect the K0.5 of binding sites for Na+ and the stoichiometry of translocation. These results suggest that intravesicular K+ and external Na+ have a dual role on the mechanism of [3H]GABA uptake: K+ acts directly on the carrier and determines the membrane polarization; Na+ is cotransported with GABA and, according to the polarization state of the membrane, it modulates the operation of the carrier in its inward GABA translocation.
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