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This Article Full Text Full Text (PDF) All Versions of this Article: 558/3/759    most recent jphysiol.2004.064311v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bissonnette, P. Articles by Lapointe, J.-Y. Search for Related Content PubMed PubMed Citation Articles by Bissonnette, P. Articles by Lapointe, J.-Y.

Groupe d'étude des protéines membranaires, département de physique, Université de Montréal, Canada

Myo-inositol is a compatible osmolyte used by cells which are challenged by variations in extracellular osmolarity, as in the renal medulla. In order to accumulate large quantities of this polyol, cells rely on Na⁺-dependent transporters such as SMIT1. We have recently identified a second Na⁺–myo-inositol cotransporter, SMIT2, which presents transport characteristics corresponding to those recently described for the apical membrane of renal proximal tubules. In order to further characterize this transport system, we transfected Madin-Darby canine kidney (MDCK) cells with rabbit SMIT2 cDNA and selected a stable clone with a high expression level. The accumulation of radiolabelled myo-inositol by this cell line is 20-fold larger than that seen in native MDCK cells. The affinity for myo-inositol of MDCK cells transfected with SMIT2 is slightly lower (K_m= 334 µM) than that found in voltage-clamped Xenopus laevis oocytes expressing SMIT2 (K_m= 120 µM). Transport studies performed using semipermeable filters showed complete apical targeting of the SMIT2 transporter. This apical localization of SMIT2 was confirmed by transport studies on purified rabbit renal brush border membrane vesicles (BBMVs). Using a purified antibody against SMIT2, we were also able to detect the SMIT2 protein (molecular mass = 66 kDa) in Western blots of BBMVs purified from SMIT2-transfected MDCK cells. SMIT2 activity was also shown to be stimulated 5-fold when submitted to 24 h hypertonic treatment (+200 mosmol l^–1). The SMIT2-MDCK cell line thus appears to be a promising model for studying SMIT2 biochemistry and regulation.

(Received 15 March 2004; accepted after revision 2 June 2004; first published online 4 June 2004)
Corresponding author P. Bissonnette: Dép. physiologie, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, Québec, Canada, H3C3J7. Email: pierre.bissonnette{at}umontreal.ca

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				R. Aouameur, S. Da Cal, P. Bissonnette, M. J. Coady, and J.-Y. Lapointe SMIT2 mediates all myo-inositol uptake in apical membranes of rat small intestine Am J Physiol Gastrointest Liver Physiol, December 1, 2007; 293(6): G1300 - G1307. [Abstract] [Full Text] [PDF]