Ion fluxes associated with excitatory amino acid transport.
Flux of substrate and charge mediated by three cloned excitatory amino acid transporters widely expressed in human brain were studied in voltage-clamped Xenopus oocytes. Superfusion of L-glutamate or D-aspartate resulted in currents due in part to electrogenic Na+ cotransport, which contributed 1 net positive charge per transport cycle. A significant additional component of the currents was due to activation of a reversible anion flux that was not thermodynamically coupled to amino acid transport. The selectivity sequence of this ligand-activated conductance was NO3- > 1- > Br- > Cl- > F-. The results suggest that these proteins mediate both transporter- and channel-like modes of permeation, providing a potential mechanism for dampening cell excitability, in addition to removal of transmitter.
Wadiche
J I
JI
Vollum Institute, Oregon Health Sciences University, Portland 97201, USA.
Amara
S G
SG
Kavanaugh
M P
MP
D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D001692:Biological Transport; D001921:Brain / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D004553:Electric Conductivity; D018846:Excitatory Amino Acids / Q000378:metabolism*; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism; D006801:Humans; D015640:Ion Channel Gating; D007473:Ion Channels / Q000502:physiology*; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D013816:Thermodynamics; D014162:Transfection; D014981:Xenopus
D002352:Carrier Proteins; D002712:Chlorides; D018846:Excitatory Amino Acids; D007473:Ion Channels; D001224:Aspartic Acid; D018698:Glutamic Acid