| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 Division of Molecular Physiology, School of Life Sciences
2 Division of Cell & Developmental Biology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
3 Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912, USA
System N (SNAT3 and SNAT5) amino acid transporters are key mediators of glutamine transport across the plasma membrane of mammalian cell types, including hepatocytes and astrocytes. We demonstrate that SNAT5 shows simultaneous bidirectional glutamine fluxes when overexpressed in Xenopus oocytes. Influx and efflux are both apparently Na+ dependent but, since they are not directly coupled, the carrier is capable of mediating net amino acid movement across the cell membrane. The apparent Km values for glutamine influx and efflux are similar (
1 mM) and the transporter behaviour is consistent with a kinetic model in which re-orientation of the carrier from outside- to inside-facing conformations (either empty or substrate loaded) is the limiting step in the transport cycle. In perfused rat liver, the observed relationship between influent (portal) glutamine concentration and net hepatic glutamine flux may be described by a simple kinetic model, assuming the balance between influx and efflux through System N determines net flux, where under physiological conditions efflux is generally saturated owing to high intracellular glutamine concentration. SNAT5 shows a more periportal mRNA distribution than SNAT3 in rat liver, indicating that SNAT5 may have particular importance for modulation of net hepatic glutamine flux.
(Received 23 December 2003;
accepted after revision 18 June 2004;
first published online 24 June 2004)
Corresponding author P. M. Taylor: Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK. Email: p.m.taylor{at}dundee.ac.uk
This article has been cited by other articles:
|
|
 |
|
  S. Broer Amino Acid Transport Across Mammalian Intestinal and Renal Epithelia Physiol Rev, January 1, 2008; 88(1): 249 - 286. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Evans, Z. Nasim, J. Brown, H. Butler, S. Kauser, H. Varoqui, J. D. Erickson, T. P. Herbert, and A. Bevington Acidosis-Sensing Glutamine Pump SNAT2 Determines Amino Acid Levels and Mammalian Target of Rapamycin Signalling to Protein Synthesis in L6 Muscle Cells J. Am. Soc. Nephrol., May 1, 2007; 18(5): 1426 - 1436. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. C. Onan, J. S. Fisher, J.-S. Ju, B. C. Fuchs, and B. P. Bode Type I Diabetes Affects Skeletal Muscle Glutamine Uptake in a Fiber-Specific Manner Experimental Biology and Medicine, October 1, 2005; 230(9): 606 - 611. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
