Enzymatic suppression of the membrane conductance associated with the glutamine transporter SNAT3 expressed in Xenopus oocytes by carbonic anhydrase II.
The transport activity of the glutamine/neutral amino acid transporter SNAT3 (former SN1, SLC38A3), expressed in oocytes of the frog Xenopus laevis is associated with a non-stoichiometrical membrane conductance selective for Na(+) and/or H(+) (Schneider, H.P., S. Bröer, A. Bröer, and J.W. Deitmer. 2007. J. Biol. Chem. 282:3788-3798). When we expressed SNAT3 in frog oocytes, the glutamine-induced membrane conductance was suppressed, when carbonic anhydrase isoform II (CAII) had been injected into the oocytes. Transport of substrate, however, was not affected by CAII. The reduction of the membrane conductance by CAII was dependent on the presence of CO(2)/HCO(3)(-), and could be reversed by blocking the catalytic activity of CAII by ethoxyzolamide (10 microM). Coexpression of wild-type CAII or a N-terminal CAII mutant with SNAT3 also reduced the SNAT3- associated membrane conductance. The catalytically inactive CAII mutant V143Y coexpressed in oocytes did not affect SNAT3-associated membrane conductance. Our results reveal a new type of interaction between CAII and a transporter-associated cation conductance, and support the hypothesis that the transport of substrate and the non-stoichiometrical ion conductance are independent of each other. This study also emphasizes the importance of carbonic anhydrase activity and the presence of CO(2)-bicarbonate buffers for membrane transport processes.
Abteilung für Allgemeine Zoologie, FB Biologie, Universitaet Kaiserslautern, D-67653 Kaiserslautern, Germany.
Alexandra
A
Weise
Holger M
HM
Becker
Joachim W
JW
Deitmer
D026921:Amino Acid Transport Systems, Neutral / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D024402:Carbonic Anhydrase II / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D004594:Electrophysiology; D004926:Escherichia coli; D005260:Female; D005786:Gene Expression Regulation; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D009154:Mutation / Q000235:genetics; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D014982:Xenopus laevis
D026921:Amino Acid Transport Systems, Neutral; D007527:Isoenzymes; C403222:system N protein 1; D024402:Carbonic Anhydrase II