title: Substrate-dependent interference of carbonic anhydrases with the glutamine transporter SNAT3-induced conductance.
abstract: The glutamine transporter SNAT3 (SLC38A3), which also transports asparagine and histidine, exchanges sodium for protons, and displays a non-stoichiometrical conductance, which is suppressed by the catalytic activity of carbonic anhydrase II (CAII). In this study, we show that this conductance of rat SNAT3, expressed in Xenopus oocytes, is also suppressed following co-expression with CAI, CAIII, CAIV, and CAII-H64A (mutant with impaired intramolecular H(+) shuttling). All CA isoforms and the CAII mutant displayed catalytic activity in intact oocytes, although in vitro studies had reported only very low catalytic activity of CAIII and CAII-H64A. The CA-mediated suppression of conductance was only observed, however, when glutamine, but not when asparagine, was the substrate. We hypothesized that this substrate specificity of the CA action might be due to the different ion selectivity induced by the different amino acid substrates, which induce currents carried by sodium and/or protons. The ion selectivity and conductance was dependent on both pH and extracellular sodium concentration for glutamine and asparagine; however the sodium dependence of the conductance, when asparagine was the substrate, was significantly greater at higher sodium concentrations, which might explain the difference in the sensitivity of the conductance to CAs. Given the presence of CAs in most cells, substrate sensing of SNAT3 would be indicated by different membrane potential changes.
authors.affiliation: Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Kaiserslautern, Germany.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Weise
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Schneider
authors.forename: Robert
authors.initials: R
authors.lastname: McKenna
authors.forename: Joachim W
authors.initials: JW
authors.lastname: Deitmer
mesh_terms: D019943:Amino Acid Substitution; D026921:Amino Acid Transport Systems, Neutral / Q000378:metabolism*; D000818:Animals; D001216:Asparagine / Q000378:metabolism; D024401:Carbonic Anhydrase I / Q000378:metabolism; D024402:Carbonic Anhydrase II / Q000378:metabolism; D024403:Carbonic Anhydrase III / Q000378:metabolism; D030741:Carbonic Anhydrase IV / Q000378:metabolism; D002256:Carbonic Anhydrases / Q000235:genetics / Q000378:metabolism*; D055724:Electrophysiological Phenomena; D006639:Histidine / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism; D014982:Xenopus laevis / Q000196:embryology / Q000378:metabolism
chemical_list: D026921:Amino Acid Transport Systems, Neutral; C403222:system N protein 1; D006639:Histidine; D001216:Asparagine; D012964:Sodium; D024401:Carbonic Anhydrase I; D024402:Carbonic Anhydrase II; D024403:Carbonic Anhydrase III; D030741:Carbonic Anhydrase IV; D002256:Carbonic Anhydrases