A stereospecific myo-inositol/D-chiro-inositol transporter in HepG2 liver cells. Identification with D-chiro-[3-3H]inositol.
D-chiro-Inositol is an epimer of myo-inositol that is found in certain mammalian glycosylphosphatidylinositol protein anchors and inositol phosphoglycans possessing insulin-like bioactivity. In order to generate a probe for metabolic studies, D-chiro-[3-3H]inositol was synthesized by selective reduction of D-chiro-3-inosose at pH 6.5 with sodium borotritide. D-chiro-[3-3H]Inositol was taken up by HepG2 human liver cells through a saturable and stereospecific pathway in which D-chiro-inositol and myo-inositol competed equally but L-chiro-inositol was not recognized. Dd-Glucose, but not L-glucose, competed for D-chiro-[3-3H]inositol uptake over glucose concentrations of 4-28 mM. Maximum transport capacity was 717 pmol/mg cell protein/3 h with a Km value of 348 microM. Uptake was reduced by 76% when sodium was eliminated from the medium and by 94% when the experiment was performed at 0 degrees C. The new myo/D-chiro-inositol transporter is distinct from the sodium-myo-inositol co-transporter found in many tissues and accounts for all of the saturable D-chiro-inositol uptake and for a portion of the saturable low affinity myo-inositol uptake in HepG2 cells. It may allow D-chiro-inositol to be used by cells in the presence of a relatively large amount of competing myo-inositol.
Ostlund
R E
RE
Metabolism Division and the Department of Psychiatry, Washington University, St. Louis, Missouri 63110, USA.
Seemayer
R
R
Gupta
S
S
Kimmel
R
R
Ostlund
E L
EL
Sherman
W R
WR
D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects; D003571:Cytochalasin B / Q000494:pharmacology; D006801:Humans; D007294:Inositol / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D010695:Phlorhizin / Q000494:pharmacology; D013237:Stereoisomerism; D014407:Tumor Cells, Cultured
D003571:Cytochalasin B; D007294:Inositol; D010695:Phlorhizin