title: Na(+)-dependent glutamate transporters (EAAT1, EAAT2, and EAAT3) of the blood-brain barrier. A mechanism for glutamate removal.
abstract: Na(+)-dependent transporters for glutamate exist on astrocytes (EAAT1 and EAAT2) and neurons (EAAT3). These transporters presumably assist in keeping the glutamate concentration low in the extracellular fluid of brain. Recently, Na(+)-dependent glutamate transport was described on the abluminal membrane of the blood-brain barrier. To determine whether the above-mentioned transporters participate in glutamate transport of the blood-brain barrier, total RNA was extracted from bovine cerebral capillaries. cDNA for EAAT1, EAAT2, and EAAT3 was observed, indicating that mRNA was present. Western blot analysis demonstrated all three transporters were expressed on abluminal membranes, but none was detectable on luminal membranes of the blood-brain barrier. Measurement of transport kinetics demonstrated voltage dependence, K(+)-dependence, and an apparent K(m) of 14 microM (aggregate of the three transporters) at a transmembrane potential of -61 mV. Inhibition of glutamate transport was observed using inhibitors specific for EAAT2 (kainic acid and dihydrokainic acid) and EAAT3 (cysteine). The relative activity of the three transporters was found to be approximately 1:3:6 for EAAT1, EAAT2, and EAAT3, respectively. These transporters may assist in maintaining low glutamate concentrations in the extracellular fluid.
authors.affiliation: Department of Physiology, Finch University of Health Science, The Chicago Medical School, North Chicago, Illinois 60064-3095, USA.
authors.forename: R L
authors.initials: RL
authors.lastname: O'Kane
authors.forename: I
authors.initials: I
authors.lastname: Martínez-López
authors.forename: M R
authors.initials: MR
authors.lastname: DeJoseph
authors.forename: J R
authors.initials: JR
authors.lastname: Viña
authors.forename: R A
authors.initials: RA
authors.lastname: Hawkins
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D027322:Amino Acid Transport System X-AG; D000818:Animals; D001692:Biological Transport; D001812:Blood-Brain Barrier; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D027342:Excitatory Amino Acid Transporter 2; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D027981:Symporters
chemical_list: D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D002352:Carrier Proteins; D027342:Excitatory Amino Acid Transporter 2; D050491:Glutamate Plasma Membrane Transport Proteins; D017981:Receptors, Neurotransmitter; D027981:Symporters; D018698:Glutamic Acid