Expression and functionality of the Na+/myo-inositol cotransporter SMIT2 in rabbit kidney.
Myo-inositol (MI) is involved in several important aspects of cell physiology including cell signaling and the control of intracellular osmolarity i.e. by serving as a "compatible osmolyte". Currently, three MI cotransporters have been identified: two are Na(+)-dependent (SMIT1 and SMIT2) and one is H(+)-dependent (HMIT) and predominantly expressed in the brain. The goal of this study was to characterize the expression of SMIT2 in rabbit kidney and to compare it to SMIT1. First, we quantified mRNA levels for both transporters using quantitative real-time PCR and found that SMIT1 was predominantly expressed in the medulla while SMIT2 was mainly in the cortex. This distribution of SMIT2 was confirmed on Western blots where an antibody raised against a SMIT2 epitope specifically detected a 75 kDa protein in both tissues. Characterization of MI transport in brush-border membrane vesicles (BBMV), in the presence of d-chiro-inositol and l-fucose to separately identify SMIT1 and SMIT2 activities, showed that only SMIT2 is expressed at the luminal side of proximal convoluted tubules. We thus conclude that, in the rabbit kidney, SMIT2 is predominantly expressed in the cortex where it is probably responsible for the apical transport of MI into the proximal tubule.
Lahjouji
Karim
K
Groupe d'Etude des Protéines Membranaires (GEPROM), département de Physiologie, Université de Montréal, Montréal, Québec, Canada H3T 1J4.
Aouameur
Rym
R
Bissonnette
Pierre
P
Coady
Michael J
MJ
Bichet
Daniel G
DG
Lapointe
Jean-Yves
JY
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D015153:Blotting, Western; D005786:Gene Expression Regulation / Q000187:drug effects; D007294:Inositol / Q000378:metabolism*; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008757:Methylglucosides / Q000494:pharmacology; D008871:Microvilli / Q000187:drug effects; D009004:Monosaccharide Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors; D022161:Transport Vesicles / Q000187:drug effects
D008757:Methylglucosides; D009004:Monosaccharide Transport Proteins; D007294:Inositol; C027020:methylglucoside; D012964:Sodium