Submitted on September 9, 2008
Revised on March 3, 2009
Accepted on April 5, 2009
AMPK activation is fiber type specific in human skeletal muscle: effects of exercise and short-term exercise training
Robert S. Lee-Young1*, Benedict J. Canny2, Damian E. Myers3, and Glenn Kevin McConell3
1 Vanderbilt University School of Medicine
2 Monash University
3 The University of Melbourne
* To whom correspondence should be addressed. E-mail: robert.s.lee-young{at}Vanderbilt.Edu.
AMP-activated protein kinase (AMPK) has been extensively studied in whole muscle biopsy samples of humans, yet the fiber type specific expression and/or activation of AMPK is unknown. We examined basal and exercise AMPK 
Thr172 phosphorylation and AMPK subunit expression (1, 2, and 
3) in type I, IIa, and IIx fibers of human skeletal muscle before and after 10 days of exercise training. Before training basal AMPK phosphorylation was greatest in type IIa fibers (P<0.05 vs. type I and IIx), whilst an acute bout of exercise increased AMPK phosphorylation in all fibers (P<0.05), with the greatest increase occurring in type IIx fibers. Exercise training significantly increased basal AMPK phosphorylation in all fibers, and the exercise-induced increases were uniformly suppressed compared with pre-training exercise. Expression of AMPK 1 and 2 was similar between fibers and was not altered by exercise training. However, AMPK 3 was differentially expressed in skeletal muscle fibers (type IIx > type IIa > type I), irrespective of training status. Thus, skeletal muscle AMPK phosphorylation and AMPK expression is fiber type specific in humans in the basal state, as well as during exercise. Our findings reveal fiber type specific differences that have been masked in previous studies examining mixed muscle samples.
