title: Mechanism of hypoxia-stimulated glucose transport in rat skeletal muscle: potential role of glycogen.
abstract: We have previously reported that exercise training is associated with enhanced insulin-stimulated glucose transport activity and inhibited hypoxia-stimulated glucose transport activity in rat epitrochlearis muscle. Here we examine the potential role of muscle glycogen in the inhibited glucose transport response to hypoxia. Three days of swim training (2 x 3 h/day) produce a 100% increase in glycogen and a 70% increase in GLUT-4 in epitrochlearis muscle. Glucose transport after 1 h of hypoxia in muscles from fed exercise-trained (ET) rats is not significantly elevated above basal and is 40% lower than that in muscles from fed sedentary (SED) rats. Glycogen levels after 1 h of hypoxia are reduced by 27 and 64% in muscles from fed ET and fed SED rats, respectively. After 2 h of hypoxia, glucose transport is significantly increased above basal in muscles from fed ET rats, but this response is still 55% lower than that in muscles from fed SED rats. After 2 h of hypoxia, glycogen is reduced by 50 and 83% in muscles from fed ET and fed SED rats, respectively. After a modified overnight fast (approximately 4.5 g of chow), the glucose transport and glycogen responses to 1 h of hypoxia are not significantly different between muscles from ET and SED rats. These findings demonstrate a strong inverse relationship between glycogen and hypoxia-stimulated glucose transport activity and that high levels of glycogen contribute to the inhibited glucose transport response to hypoxia. Furthermore, failure of the overexpression of GLUT-4 after exercise training to enhance the glucose transport response to contraction/hypoxia suggests selective targeting of the additional GLUT-4 to the insulin-responsive pool.
authors.affiliation: Experimental Diabetes, Metabolism, and Nutrition Section, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda 20892-1420, USA.
authors.forename: T H
authors.initials: TH
authors.lastname: Reynolds
authors.forename: J T
authors.initials: JT
authors.lastname: Brozinick
authors.forename: M A
authors.initials: MA
authors.lastname: Rogers
authors.forename: S W
authors.initials: SW
authors.lastname: Cushman
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D006003:Glycogen / Q000502:physiology*; D000860:Hypoxia / Q000378:metabolism*; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000378:metabolism*; D010805:Physical Conditioning, Animal; D051381:Rats; D017208:Rats, Wistar
chemical_list: D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495694:Slc2a4 protein, rat; D006003:Glycogen; D005947:Glucose