Mouse GLUT9: evidences for a urate uniporter.
GLUT9 (SLC2A9) is a newly described urate transporter whose function, characteristics, and localization have just started to be elucidated. Some transport properties of human GLUT9 have been studied in the Xenopus laevis oocyte expression system, but the type of transport (uniport, coupled transport system, stoichiometry ... .) is still largely unknown. We used the same experimental system to characterize in more detail the transport properties of mouse GLUT9, its sensitivity to several uricosuric drugs, and the specificities of two splice variants, mGLUT9a and mGLUT9b. [(14)C]urate uptake measurements show that both splice variants are high-capacity urate transporters and have a K(m) of approximately 650 microM. The well-known uricosuric agents benzbromarone (500 microM) and losartan (1 mM) inhibit GLUT9-mediated urate uptake by 90 and 50%, respectively. Surprisingly, phloretin, a glucose-transporter blocker, inhibits [(14)C]urate uptake by approximately 50% at 1 mM. Electrophysiological measurements suggest that urate transport by mouse GLUT9 is electrogenic and voltage dependent, but independent of the Na(+) and Cl(-) transmembrane gradients. Taken together, our results suggest that GLUT9 works as a urate (anion) uniporter. Finally, we show by RT-PCR performed on RNA from mouse kidney microdissected tubules that GLUT9a is expressed at low levels in proximal tubules, while GLUT9b is specifically expressed in distal convoluted and connecting tubules. Expression of mouse GLUT9 in the kidney differs from that of human GLUT9, which could account for species differences in urate handling.
Bibert
Stéphanie
S
Dept. of Pharmacology and Toxicology, Univ. of Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland.
Hess
Solange Kharoubi
SK
Firsov
Dmitri
D
Thorens
Bernard
B
Geering
Käthi
K
Horisberger
Jean-Daniel
JD
Bonny
Olivier
O
D000818:Animals; D001553:Benzbromarone / Q000494:pharmacology; D001692:Biological Transport; D002712:Chlorides / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D051246:Glucose Transport Proteins, Facilitative / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051273:Glucose Transporter Type 2 / Q000378:metabolism; D007700:Kinetics; D019808:Losartan / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D009399:Nephrons / Q000378:metabolism*; D009865:Oocytes; D027361:Organic Anion Transporters / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010693:Phloretin / Q000494:pharmacology; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000032:analysis; D012964:Sodium / Q000378:metabolism; D013045:Species Specificity; D014527:Uric Acid / Q000378:metabolism*; D014528:Uricosuric Agents / Q000494:pharmacology; D014982:Xenopus laevis
D002712:Chlorides; D051246:Glucose Transport Proteins, Facilitative; D051273:Glucose Transporter Type 2; D027361:Organic Anion Transporters; D020033:Protein Isoforms; D012333:RNA, Messenger; C495682:Slc2a2 protein, mouse; C498775:Slc2a9 protein, mouse; D014528:Uricosuric Agents; C103862:urate transporter; D014527:Uric Acid; D001553:Benzbromarone; D012964:Sodium; D005947:Glucose; D019808:Losartan; D010693:Phloretin