The anion conductance of the glutamate transporter EAAC1 depends on the direction of glutamate transport.
The steady-state and pre-steady-state kinetics of glutamate transport by the neuronal glutamate transporter EAAC1 were determined under conditions of outward glutamate transport and compared to those found for the inward transport mode. In both transport modes, the glutamate-induced current is composed of two components, the coupled transport current and the uncoupled anion current, and inhibited by a specific non-transportable inhibitor. Furthermore, the glutamate-independent leak current is observed in both transport modes. Upon a glutamate concentration jump outward transport currents show a distinct transient phase that deactivates within 15 ms. The results demonstrate that the general properties of EAAC1 are symmetric, but the rates of substrate transport and anion flux are asymmetric with respect to the orientation of the substrate binding site in the membrane. Therefore, the EAAC1 anion conductance differs from normal ligand-gated ion channels in that it can be activated by glutamate and Na(+) from both sides of the membrane.
Watzke
N
N
Max-Planck-Institut für Biophysik, Kennedyallee 70, D-60596 Frankfurt, Germany.
Grewer
C
C
D027322:Amino Acid Transport System X-AG; D000818:Animals; D000838:Anions / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D004553:Electric Conductivity; D050580:Excitatory Amino Acid Transporter 3; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D017136:Ion Transport; D007700:Kinetics; D008954:Models, Biological; D010782:Photolysis; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D027981:Symporters
D027322:Amino Acid Transport System X-AG; D000838:Anions; D002352:Carrier Proteins; D050580:Excitatory Amino Acid Transporter 3; D050491:Glutamate Plasma Membrane Transport Proteins; D011994:Recombinant Proteins; C493400:SLC1A1 protein, human; C493398:Slc1a1 protein, rat; D027981:Symporters; D018698:Glutamic Acid; D012964:Sodium