Glutamate modifies ion conduction and voltage-dependent gating of excitatory amino acid transporter-associated anion channels.
Excitatory amino acid transporters (EAATs) mediate two distinct transport processes, a stoichiometrically coupled transport of glutamate, Na+, K+, and H+, and a pore-mediated anion conductance. We studied the anion conductance associated with two mammalian EAAT isoforms, hEAAT2 and rEAAT4, using whole-cell patch clamp recording on transfected mammalian cells. Both isoforms exhibited constitutively active, multiply occupied anion pores that were functionally modified by various steps of the Glu/Na+/H+/K+ transport cycle. Permeability and conductivity ratios were distinct for cells dialyzed with Na(+)- or K(+)-based internal solution, and application of external glutamate altered anion permeability ratios and the concentration dependence of the anion influx. EAAT4 but not EAAT2 anion channels displayed voltage-dependent gating that was modified by glutamate. These results are incompatible with the notion that glutamate only increases the open probability of the anion pore associated with glutamate transporters and demonstrate unique gating mechanisms of EAAT-associated anion channels.
D027322:Amino Acid Transport System X-AG; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D000838:Anions; D001692:Biological Transport; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D027342:Excitatory Amino Acid Transporter 2 / Q000737:chemistry / Q000378:metabolism*; D050581:Excitatory Amino Acid Transporter 4; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D007477:Ions; D007700:Kinetics; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000737:chemistry; D011485:Protein Binding; D020033:Protein Isoforms; D051381:Rats; D017470:Receptors, Glutamate / Q000737:chemistry / Q000378:metabolism*; D012964:Sodium / Q000737:chemistry; D027981:Symporters; D013997:Time Factors; D014162:Transfection
D027322:Amino Acid Transport System X-AG; D000596:Amino Acids; D000838:Anions; D027342:Excitatory Amino Acid Transporter 2; D050581:Excitatory Amino Acid Transporter 4; D050491:Glutamate Plasma Membrane Transport Proteins; D007477:Ions; D020033:Protein Isoforms; D017470:Receptors, Glutamate; C493397:SLC1A2 protein, human; C493391:SLC1A6 protein, human; C493395:Slc1a2 protein, rat; C493389:Slc1a6 protein, rat; D027981:Symporters; D018698:Glutamic Acid; D012964:Sodium; D011188:Potassium