title: Muscle Na+-K+-ATPase response during 16 h of heavy intermittent cycle exercise.
abstract: This study investigated the effects of a 16-h protocol of heavy intermittent exercise on the intrinsic activity and protein and isoform content of skeletal muscle Na(+)-K(+)-ATPase. The protocol consisted of 6 min of exercise performed once per hour at approximately 91% peak aerobic power (Vo(2 peak)) with tissue sampling from vastus lateralis before (B) and immediately after repetitions 1 (R1), 2 (R2), 9 (R9), and 16 (R16). Eleven untrained volunteers with a Vo(2 peak) of 44.3 +/- 2.3 ml x kg(-1) x min(-1) participated in the study. Maximal Na(+)-K(+)-ATPase activity (V(max), in nmol x mg protein(-1) x h(-1)) as measured by the 3-O-methylfluorescein K(+)-stimulated phosphatase assay was reduced (P < 0.05) by approximately 15% with exercise regardless of the number of repetitions performed. In addition, V(max) at R9 and R16 was lower (P < 0.05) than at R1 and R2. Vanadate-facilitated [(3)H]ouabain determination of Na(+)-K(+)-ATPase content (maximum binding capacity, pmol/g wet wt), although unaltered by exercise, increased (P < 0.05) 8.3% by R9 with no further increase observed at R16. Assessment of relative changes in isoform abundance measured at B as determined by quantitative immunoblotting showed a 26% increase (P < 0.05) in the alpha(2)-isoform by R2 and a 29% increase in alpha(3) by R9. At R16, beta(3) was lower (P < 0.05) than at R2 and R9. No changes were observed in alpha(1), beta(1), or beta(2). It is concluded that repeated sessions of heavy exercise, although resulting in increases in the alpha(2)- and alpha(3)-isoforms and decreases in beta(3)-isoform, also result in depression in maximal catalytic activity.
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: G P
authors.initials: GP
authors.lastname: Holloway
authors.forename: J W
authors.initials: JW
authors.lastname: Moule
authors.forename: J
authors.initials: J
authors.lastname: Ouyang
authors.forename: D
authors.initials: D
authors.lastname: Ranney
authors.forename: A R
authors.initials: AR
authors.lastname: Tupling
mesh_terms: D000328:Adult; D001642:Bicycling; D004837:Epinephrine / Q000097:blood; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000378:metabolism; D009638:Norepinephrine / Q000097:blood; D010042:Ouabain / Q000378:metabolism; D005082:Physical Exertion / Q000502:physiology*; D011485:Protein Binding; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013997:Time Factors
chemical_list: D007527:Isoenzymes; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D009638:Norepinephrine; D004837:Epinephrine