title: Dual role of K+ and Na+ on the transport of [3H]-gamma-aminobutyric acid by synaptic plasma membrane vesicles.
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.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002540:Cerebral Cortex / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D011188:Potassium / Q000502:physiology*; D012756:Sheep; D012964:Sodium / Q000502:physiology*; D013570:Synaptic Membranes / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism*; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000493:pharmacokinetics*
chemical_list: D014316:Tritium; D005680:gamma-Aminobutyric Acid; D012964:Sodium; D011188:Potassium