title: Increments in skeletal muscle GLUT-1 and GLUT-4 after endurance training in humans.
abstract: We investigated the time course of training-induced changes in the expression of GLUT-1 and GLUT-4 in human skeletal muscle. Seven healthy males trained for 2 h/day (approximately 60% pretraining VO2peak) for 31 days (31D). Muscle biopsies were obtained before training (PRE) and after 5 (5D) and 31 days (31D) of training. Training resulted in progressive increases in muscle GLUT-4 with increasing training duration (PRE<5D<31D; P<0.01). Muscle GLUT-1 content was also increased (P<0.05) after training; however, the increase was not observed until 31D (131%). Increases in muscle hexokinase (HK) activity were complete by 5D (P<0.01). Muscle malate dehydrogenase activity was not elevated after 5D of training but was increased (+35%; P<0.01) at 31D. Results from this study show that increases in both GLUT-4 and HK represent early training-induced adaptations to prolonged exercise training. As training progresses, further increases in GLUT-4, but not HK, occur in conjunction with an increase in muscle mitochondrial potential and GLUT-1.
authors.affiliation: Department of Kinesiology, University of Waterloo, Ontario, Canada.
authors.forename: S M
authors.initials: SM
authors.lastname: Phillips
authors.forename: X X
authors.initials: XX
authors.lastname: Han
authors.forename: H J
authors.initials: HJ
authors.lastname: Green
authors.forename: A
authors.initials: A
authors.lastname: Bonen
mesh_terms: D000328:Adult; D001706:Biopsy; D015444:Exercise; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D006593:Hexokinase / Q000378:metabolism; D006801:Humans; D008291:Malate Dehydrogenase / Q000378:metabolism; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D010807:Physical Endurance; D012044:Regression Analysis; D013997:Time Factors
chemical_list: D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495677:SLC2A1 protein, human; C495692:SLC2A4 protein, human; D008291:Malate Dehydrogenase; D006593:Hexokinase