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Am J Physiol Regul Integr Comp Physiol 293: R821-R828, 2007. First published April 25, 2007; doi:10.1152/ajpregu.00796.2006
0363-6119/07 $8.00
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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Skeletal muscle nNOSµ protein content is increased by exercise training in humans

Glenn K. McConell,1 Scott J. Bradley,2,3 Terry J. Stephens,2 Benedict J. Canny,2 Bronwyn A. Kingwell,3 and Robert S. Lee-Young1

1Department of Physiology, The University of Melbourne, Parkville; 2Department of Physiology, Monash University, Clayton; and 3Alfred & Baker Medical Unit, Baker Heart Research Institute, Prahran, Victoria, Australia

Submitted 13 November 2006 ; accepted in final form 20 April 2007

The major isoform of nitric oxide synthase (NOS) in skeletal muscle is the splice variant of neuronal NOS, termed nNOSµ. Exercise training increases nNOSµ protein levels in rat skeletal muscle, but data in humans are conflicting. We performed two studies to determine 1) whether resting nNOSµ protein expression is greater in skeletal muscle of 10 endurance-trained athletes compared with 11 sedentary individuals (study 1) and 2) whether intense short-term (10 days) exercise training increases resting nNOSµ protein (within whole muscle and also within types I, IIa, and IIx fibers) in eight sedentary individuals (study 2). In study 1, nNOSµ protein was ~60% higher (P < 0.05) in endurance-trained athletes compared with the sedentary participants. In study 2, nNOSµ protein expression was similar in types I, IIa, and IIx fibers before training. Ten days of intense exercise training significantly (P < 0.05) increased nNOSµ protein levels in types I, IIa, and IIx fibers, a finding that was validated by using whole muscle samples. Endothelial NOS and inducible NOS protein were barely detectable in the skeletal muscle samples. In conclusion, nNOSµ protein expression is greater in endurance-trained individuals when compared with sedentary individuals. Ten days of intense exercise is also sufficient to increase nNOSµ expression in untrained individuals, due to uniform increases of nNOSµ within types I, IIa, and IIx fibers.

nitric oxide; nitric oxide synthase; immunohistochemistry


Address for reprint requests and other correspondence: G. McConell, Dept. of Physiology, The Univ. of Melbourne, Parkville, Victoria 3010, Australia (e-mail: mcconell{at}unimelb.edu.au)






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