title: Zn(2+) inhibits the anion conductance of the glutamate transporter EEAT4.
abstract: Glutamate transport by the excitatory amino acid transporters (EAATs) is coupled to the co-transport of 3 Na(+) ions and 1 H(+) and the counter-transport of 1 K(+) ion, which ensures that extracellular glutamate concentrations are maintained in the submicromolar range. In addition to the coupled ion fluxes, glutamate transport activates an uncoupled anion conductance that does not influence the rate or direction of transport but may have the capacity to influence the excitability of the cell. Free Zn(2+) ions are often co-localized with glutamate in the central nervous system and have the capacity to modulate the dynamics of excitatory neurotransmission. In this study we demonstrate that Zn(2+) ions inhibit the uncoupled anion conductance and also reduce the affinity of L-aspartate for EAAT4. The molecular basis for this effect was investigated using site-directed mutagenesis. Two histidine residues in the extracellular loop between transmembrane domains three and four of EAAT4 appear to confer Zn(2+) inhibition of the anion conductance.
authors.affiliation: Department of Pharmacology, University of Sydney, New South Wales, 2006, Australia.
authors.forename: A D
authors.initials: AD
authors.lastname: Mitrovic
authors.forename: F
authors.initials: F
authors.lastname: Plesko
authors.forename: R J
authors.initials: RJ
authors.lastname: Vandenberg
mesh_terms: D027322:Amino Acid Transport System X-AG; D018118:Chloride Channels / Q000378:metabolism; D050581:Excitatory Amino Acid Transporter 4; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D017136:Ion Transport; D017470:Receptors, Glutamate / Q000378:metabolism*; D027981:Symporters; D009435:Synaptic Transmission; D015032:Zinc / Q000378:metabolism*
chemical_list: D027322:Amino Acid Transport System X-AG; D018118:Chloride Channels; D050581:Excitatory Amino Acid Transporter 4; D050491:Glutamate Plasma Membrane Transport Proteins; D017470:Receptors, Glutamate; C493391:SLC1A6 protein, human; D027981:Symporters; D018698:Glutamic Acid; D015032:Zinc