title: Use of hexose transport mutants to examine the expression and properties of the rat myoblast GLUT 1 transport process.
abstract: Rat L6 myoblasts were recently shown to possess the GLUT 1, 3 and 4 transporters, and not the GLUT 2 isoform [1]. This investigation examined the expression and properties of the GLUT 1 isoform. GLUT 1 transcript level was significantly reduced in cells grown at high densities and during myogenic differentiation. A comparison of the GLUT 1 and 4 transcript levels in myogenesis-competent and impaired cells revealed an inverse relationship between these two isoforms. This relationship was confirmed by studies using two independent spontaneous GLUT 3- GLUT 4- mutants, M1 and M3. These mutants possessed very high level of the GLUT 1 isoform, but negligible amount of the GLUT 3 and 4 isoforms. GLUT 1 expression was also subject to positive regulation. Glucose starvation was found to increase not only the levels of the GLUT 1 transcript and transporter, but also the intrinsic activity of the GLUT 1 transporter. Studies with M1 and M3 mutants revealed that the GLUT 1 transporter was not functional in glucose-grown cells, even though it was present at a very high level in the plasma membrane. This transporter became functional when cells were starved for glucose. The functional GLUT 1 transporter had an apparent Km value of around 0.9 mM, and was sensitive to cytochalasin B, phloretin, phlorizin and pCMBS.
authors.affiliation: Department of Biochemistry, University of Western Ontario, London, Canada.
authors.forename: Z
authors.initials: Z
authors.lastname: Lu
authors.forename: L
authors.initials: L
authors.lastname: Xia
authors.forename: O T
authors.initials: OT
authors.lastname: Mesmer
authors.forename: T C
authors.initials: TC
authors.lastname: Lo
mesh_terms: D019325:3-O-Methylglucose; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D015152:Blotting, Northern; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D015342:DNA Probes; D003847:Deoxyglucose / Q000378:metabolism; D005632:Fructose / Q000378:metabolism; D005690:Galactose / Q000494:pharmacology; D015870:Gene Expression; D005786:Gene Expression Regulation; D005947:Glucose / Q000378:metabolism; D051272:Glucose Transporter Type 1; D051274:Glucose Transporter Type 3; D051275:Glucose Transporter Type 4; D007700:Kinetics; D008757:Methylglucosides / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000096:biosynthesis* / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D009154:Mutation; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger / Q000096:biosynthesis / Q000302:isolation & purification; D051381:Rats; D014158:Transcription, Genetic
chemical_list: D015342:DNA Probes; D051272:Glucose Transporter Type 1; D051274:Glucose Transporter Type 3; D051275:Glucose Transporter Type 4; D008757:Methylglucosides; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; C495679:Slc2a1 protein, rat; C495690:Slc2a3 protein, rat; C495694:Slc2a4 protein, rat; D019325:3-O-Methylglucose; D005632:Fructose; D003847:Deoxyglucose; D005947:Glucose; D005690:Galactose