Na+ transport by the neural glutamine transporter ATA1.
Transfer of glutamine between astrocytes and neurons is an essential part of the glutamate-glutamine cycle in the brain. Here we have investigated how the neural glutamine transporter (rATA1/GlnT) works. Rat ATA1 was expressed in Xenopus laevis oocytes and examined using two-electrode voltage-clamp recordings, ion-sensitive microelectrodes and tracer flux experiments. Glutamine transport via rATA1 was electrogenic and caused inward currents that did not reverse at positive holding potentials. Currents were induced by a variety of neutral amino acids in the following relative order Ala>Ser/Gln/Asn/His/Cys/Met >MeAIB/Gly>Thr/Pro/Tyr/Val, where MeAIB is the amino acid analogue N-methylaminoisobutyric acid. The uptake of glutamine and the corresponding currents depended on Na+ and pH. Hill-coefficient and flux studies with 22NaCl indicated a cotransport stoichiometry 1 Na+ per transport cycle. The transporter also showed uncoupled Na+ transport, particularly when alanine was used as the substrate. Although substrate uptake increased strongly with increasing pH, no change of intracellular pH was observed during transport. A decrease of the intracellular pH similarly inhibited glutamine transport via ATA1, suggesting that the pH dependence was an allosteric effect on the transporter.
Albers
A
A
Physiologisches Institut der Universität, Gmelinstr. 5, 72076 Tübingen, Germany.
Bröer
A
A
Wagner
C A
CA
Setiawan
I
I
Lang
P A
PA
Kranz
E U
EU
Lang
F
F
Bröer
S
S
D026924:Amino Acid Transport System A / Q000235:genetics / Q000378:metabolism*; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000378:metabolism*; D004553:Electric Conductivity; D005260:Female; D015870:Gene Expression; D005973:Glutamine / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials; D008839:Microelectrodes; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D014162:Transfection; D014982:Xenopus laevis
D026924:Amino Acid Transport System A; D000596:Amino Acids; D011994:Recombinant Proteins; C486716:Slc38a1 protein, rat; D005973:Glutamine; D012964:Sodium