title: Effects of limb immobilization on cytochrome c oxidase activity and GLUT4 and GLUT5 protein expression in human skeletal muscle.
abstract: 1. We investigated the effects of limb immobilization (for 1 or 6 weeks) in a long leg cast after a closed tibial fracture (n = 11). Biopsies of vastus lateralis were taken on admission and after either 1 week (n = 5) or 6 weeks (n = 6) and analysed for muscle fibre type characteristics, cytochrome c oxidase activity and the abundance of GLUT4 and GLUT5 hexose transporters. 2. After 1 week of immobilization there was a significant decrease (8%) in the cross-sectional area of type I, but not type II, muscle fibers and in the protein-DNA ratio (16%) compared with the initial biopsy. Six weeks of immobilization led to further muscle atrophy compared with the initial biopsy and a further reduction in the cross-sectional area of both type I and II fibres (29% and 36% decrease respectively) and in the protein-DNA ratio (25%). No changes were observed in the free leg after 1 week. However, at th end of the 6 week study period, the cross-sectional area of boty type I and II fibres of the free leg were increased (7% and 5%) and there was significant increase in the protein-DNA ratio (14%), indicating a net increase in muscle protein content. 3. Assay for cytochrome c oxidase activity showed significant reduction after 1 (30%) or 6 weeks (36%) of immobilization, reflecting a reduced capacity for oxidative metabolism. No significant changes in activity were observed in muscle from the free leg after 1 or 6 weeks of study. 4. The concentrations of GLUT4 and GLUT5 protein were determined by Western blot analysis. Limb immobilization induced a marked (50%) reduction in muscle GLUT4 protein concentration after 1 week that persisted for 6 weeks. A transient but significant increase (approximately twofold) in GLUT4 concentration was detected in muscle from the free leg after 1 week, but this returned to pre-imobilization values at 6 week. Unlike GLUT4, no significant changes in the abundance of the GLUT5 protein were detected in either the immobilized or free leg at the end of the 1 or 6 week periods. 5. The present findings indicate that disuse rapidly induces a selective loss of activity and abundance of some non-myofibrillar proteins in humans. The decrease in GLUT4 protein abundance and cytochrome c oxidase activity during muscle disuse is consistent with a decreased capacity for glucose uptake and with a lower oxidative potential of inactive muscle. The lack of any major changes in GLUT5 protein abundance during limb immobilization indicates that the expression of some non-myofibrillar proteins is differentially regulated in response to muscle disuse.
authors.affiliation: Department of Anatomy and Physiology, University of Dundee, Scotland, U.K.
authors.forename: S J
authors.initials: SJ
authors.lastname: Blakemore
authors.forename: P K
authors.initials: PK
authors.lastname: Rickhuss
authors.forename: P W
authors.initials: PW
authors.lastname: Watt
authors.forename: M J
authors.initials: MJ
authors.lastname: Rennie
authors.forename: H S
authors.initials: HS
authors.lastname: Hundal
mesh_terms: D000328:Adult; D015153:Blotting, Western; D004247:DNA / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism*; D005260:Female; D051275:Glucose Transporter Type 4; D051296:Glucose Transporter Type 5; D006801:Humans; D007103:Immobilization / Q000502:physiology*; D007866:Leg; D008297:Male; D008875:Middle Aged; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D011897:Random Allocation; D013997:Time Factors
chemical_list: D051275:Glucose Transporter Type 4; D051296:Glucose Transporter Type 5; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495692:SLC2A4 protein, human; D004247:DNA; D003576:Electron Transport Complex IV