Human sodium/inositol cotransporter 2 (SMIT2) transports inositols but not glucose in L6 cells.
To characterize the function of the sodium/inositol symporter SMIT2 in skeletal muscle, human SMIT2 cDNA was transfected into L6 myoblasts using pcDNA3.1 expression vector. Compared with the pcDNA3.1 vector only transfection, this overexpression increased the uptake of [(3)H]D-chiro-inositol (DCI) by 159-fold. [(3)H]myo-Inositol uptake increased by 37-fold. In contrast, [(14)C]D-glucose, [(14)C]2-deoxy-D-glucose, or [(14)C]3-O-methyl-D-glucose uptake remained unchanged in the presence of either 0, 5.5, or 25 mM unlabeled glucose. The K(m) of DCI and myo-inositol for DCI uptake was 111.0 and 158.0 microM, respectively, whereas glucose competed for DCI uptake with a K(i) of 6.1 mM. Insulin treatment of non-transfected L6 cells (2 microM for 24 h) increased [(3)H]DCI specific uptake 18-fold. DCI transport is up regulated by insulin and competitively inhibited by millimolar levels of glucose. Therefore, expression and/or function of SMIT2, a high affinity transporter specific for DCI and myo-inositol, may be reduced in diabetes mellitus, insulin resistance and polycystic ovary syndrome causing the abnormal DCI metabolism observed in these conditions.
Lin
Xiaobo
X
Division of Endocrinology, Metabolism, and Lipid Research, Department of Medicine, Washington University School of Medicine, 660 South Euclid Avenue Box 8127, St. Louis, MO 63110, USA.
Ma
Lina
L
Fitzgerald
Robin L
RL
Ostlund
Richard E
RE
D016475:3T3 Cells; D000818:Animals; D001692:Biological Transport; D006528:Carcinoma, Hepatocellular; D045744:Cell Line, Tumor; D017931:DNA Primers; D018076:DNA, Complementary; D015971:Gene Expression Regulation, Enzymologic; D005947:Glucose / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007294:Inositol / Q000378:metabolism; D007700:Kinetics; D008113:Liver Neoplasms; D051379:Mice; D012333:RNA, Messenger / Q000235:genetics; D015183:Restriction Mapping; D020133:Reverse Transcriptase Polymerase Chain Reaction; D027981:Symporters / Q000235:genetics* / Q000378:metabolism*
D017931:DNA Primers; D018076:DNA, Complementary; D006360:Heat-Shock Proteins; D012333:RNA, Messenger; D027981:Symporters; C073884:SLC5A3 protein, human; D007294:Inositol; D005947:Glucose