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Am J Physiol Endocrinol Metab (May 8, 2007). doi:10.1152/ajpendo.00004.2007
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Submitted on January 3, 2007
Accepted on April 30, 2007

Muscle Na+-K+-ATPase Response During 16 Hours of Heavy Intermittent Cycle Exercise

H. J. Green1*, T. A. Duhamel1, Graham Paul Holloway2, John Moule3, J. Ouyang3, Don Ranney3, and A. Russell Tupling3

1 Department of Kinesiology, University of Waterloo, Waterloo, Canada
2 Human Health and Nutritional Sciences, University of Guelph, Guelph, Canada
3 Kinesiology, University of Waterloo, Waterloo, Canada

* To whom correspondence should be addressed. E-mail: green{at}healthy.uwaterloo.ca.

This study investigated the effects of a 16 hour protocol of heavy intermittent exercise on the intrinsic activity, protein and isoform content of skeletal muscle Na+-K+-ATPase. The protocol consisted of 6 min of exercise performed once per hour at ~91% peak aerobic power (VO2peak) with tissue sampling from vastus lateralis before (B) and immediately after (A) repetitions 1 (R1), 2 (R2), 9 (R9) and 16 (R16). Eleven untrained volunteers with a VO2peak of 44.3±2.3 ml.kg.-1min-1 participated in the study. Maximal Na+-K+-ATPase activity (Vmax, nmol.mg protein-1.h-1) as measured by the 3-O-methylfluorescein K+-stimulated phosphatase assay (3-O-MFPase) was reduced (P<0.05) by ~15% with exercise regardless of the number of repetitions performed. In addition, Vmax at R9 and R16 was lower (P<0.05) than at R1 and R2. Vanadate-facilitated [3H] ouabain determination of Na+-K+-ATPase content ({beta}max, 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 and decreases in {beta}3 isoform, also results in depression in maximal catalytic activity.




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