title: Glucose supplements increase human muscle in vitro Na+-K+-ATPase activity during prolonged exercise.
abstract: Regulation of maximal Na(+)-K(+)-ATPase activity in vastus lateralis muscle was investigated in response to prolonged exercise with (G) and without (NG) oral glucose supplements. Fifteen untrained volunteers (14 males and 1 female) with a peak aerobic power (Vo(2)(peak)) of 44.8 +/- 1.9 ml.kg(-1).min(-1); mean +/- SE cycled at approximately 57% Vo(2)(peak) to fatigue during both NG (artificial sweeteners) and G (6.13 +/- 0.09% glucose) in randomized order. Consumption of beverage began at 30 min and continued every 15 min until fatigue. Time to fatigue was increased (P < 0.05) in G compared with NG (137 +/- 7 vs. 115 +/- 6 min). Maximal Na(+)-K(+)-ATPase activity (V(max)) as measured by the 3-O-methylfluorescein phosphatase assay (nmol.mg(-1).h(-1)) was not different between conditions prior to exercise (85.2 +/- 3.3 or 86.0 +/- 3.9), at 30 min (91.4 +/- 4.7 vs. 91.9 +/- 4.1) and at fatigue (92.8 +/- 4.3 vs. 100 +/- 5.0) but was higher (P < 0.05) in G at 90 min (86.7 +/- 4.2 vs. 109 +/- 4.1). Na(+)-K(+)-ATPase content (beta(max)) measured by the vanadate facilitated [(3)H]ouabain-binding technique (pmol/g wet wt) although elevated (P < 0.05) by exercise (0<30, 90, and fatigue) was not different between NG and G. At 60 and 90 min of exercise, blood glucose was higher (P < 0.05) in G compared with NG. The G condition also resulted in higher (P < 0.05) serum insulin at similar time points to glucose and lower (P < 0.05) plasma epinephrine and norepinephrine at 90 min of exercise and at fatigue. These results suggest that G results in an increase in V(max) by mechanisms that are unclear.
authors.affiliation: Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada. green@healthy.uwaterloo.ca
authors.forename: H J
authors.initials: HJ
authors.lastname: Green
authors.forename: T A
authors.initials: TA
authors.lastname: Duhamel
authors.forename: K P
authors.initials: KP
authors.lastname: Foley
authors.forename: J
authors.initials: J
authors.lastname: Ouyang
authors.forename: I C
authors.initials: IC
authors.lastname: Smith
authors.forename: R D
authors.initials: RD
authors.lastname: Stewart
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold / Q000187:drug effects; D001786:Blood Glucose / Q000378:metabolism; D004837:Epinephrine / Q000097:blood; D015444:Exercise / Q000502:physiology*; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D006003:Glycogen / Q000378:metabolism; D006728:Hormones / Q000097:blood; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D007700:Kinetics; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000201:enzymology*; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000187:drug effects / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D006728:Hormones; D007295:Inositol Phosphates; D006003:Glycogen; D000254:Sodium-Potassium-Exchanging ATPase; D005947:Glucose; D009638:Norepinephrine; D004837:Epinephrine