title: Functional properties of the retinal glutamate transporters GLT-1c and EAAT5.
abstract: In the mammalian retina, glutamate uptake is mediated by members of a family of glutamate transporters known as "excitatory amino acid transporters (EAATs)." Here we cloned and functionally characterized two retinal EAATs from mouse, the GLT-1/EAAT2 splice variant GLT-1c, and EAAT5. EAATs are glutamate transporters and anion-selective ion channels, and we used heterologous expression in mammalian cells, patch-clamp recordings and noise analysis to study and compare glutamate transport and anion channel properties of both EAAT isoforms. We found GLT-1c to be an effective glutamate transporter with high affinity for Na(+) and glutamate that resembles original GLT-1/EAAT2 in all tested functional aspects. EAAT5 exhibits glutamate transport rates too low to be accurately measured in our experimental system, with significantly lower affinities for Na(+) and glutamate than GLT-1c. Non-stationary noise analysis demonstrated that GLT-1c and EAAT5 also differ in single-channel current amplitudes of associated anion channels. Unitary current amplitudes of EAAT5 anion channels turned out to be approximately twice as high as single-channel amplitudes of GLT-1c. Moreover, at negative potentials open probabilities of EAAT5 anion channels were much larger than for GLT-1c. Our data illustrate unique functional properties of EAAT5, being a low-affinity and low-capacity glutamate transport system, with an anion channel optimized for anion conduction in the negative voltage range.
authors.affiliation: From the Institute of Complex Systems, Zelluläre Biophysik, Forschungszentrum Jülich, Leo-Brandt-Straβe, 52428 Jülich, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Schneider
authors.forename: Sönke
authors.initials: S
authors.lastname: Cordeiro
authors.forename: Jan-Philipp
authors.initials: JP
authors.lastname: Machtens
authors.forename: Simona
authors.initials: S
authors.lastname: Braams
authors.forename: Thomas
authors.initials: T
authors.lastname: Rauen
authors.forename: Christoph
authors.initials: C
authors.lastname: Fahlke
mesh_terms: D000818:Animals; D027342:Excitatory Amino Acid Transporter 2 / Q000235:genetics / Q000378:metabolism*; D050582:Excitatory Amino Acid Transporter 5 / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D017136:Ion Transport / Q000502:physiology; D051379:Mice; D012160:Retina / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
chemical_list: D027342:Excitatory Amino Acid Transporter 2; D050582:Excitatory Amino Acid Transporter 5; C493396:Slc1a2 protein, mouse; C493387:Slc1a7 protein, mouse; D018698:Glutamic Acid; D012964:Sodium
keywords: Excitatory Amino Acid Transporter; Glutamate; Ion Channels; Neurotransmitter Transport; Patch Clamp; Retina