The Journal of General Physiology
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Published online July 30, 2007
doi:10.1085/jgp.200709809
The Journal of General Physiology, Vol. 130, No. 2, 203-215
The Rockefeller University Press, 0022-1295 $30.00
© 2007 Weise et al.
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ARTICLE

 Enzymatic Suppression of the Membrane Conductance Associated with the Glutamine Transporter SNAT3 Expressed in Xenopus Oocytes by Carbonic Anhydrase II



Alexandra Weise, Holger M. Becker, and Joachim W. Deitmer

Abteilung für Allgemeine Zoologie, FB Biologie, Universitaet Kaiserslautern, D-67653 Kaiserslautern, Germany

Correspondence to Joachim W. Deitmer: deitmer{at}biologie.uni-kl.de

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 CO2/HCO3–, and could be reversed by blocking the catalytic activity of CAII by ethoxyzolamide (10 µM). 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 CO2-bicarbonate buffers for membrane transport processes.

Abbreviations used in this paper: AE, anion exchanger; CAII, carbonic anhydrase isoform II; EZA, ethoxyzolamide; NBC, sodium-bicarbonate cotransporter; NHE, sodium-hydrogen exchanger.


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A. Weise, H. M. Becker, and J. W. Deitmer
Enzymatic Suppression of the Membrane Conductance Associated with the Glutamine Transporter SNAT3 Expressed in Xenopus Oocytes by Carbonic Anhydrase II
J. Cell Biol., August 9, 2007; 178(4): i7 - i7.
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