Submitted on March 24, 2006
Accepted on March 26, 2008
Paradoxical effects of endurance training and chronic hypoxia on myofibrillar ATPase activity
Belle Roels1*, Carlo Reggiani2, Cyril Reboul3, Corinne Lionne4, Bogdan Iorga4, Philippe Obert3, Stephane Tanguy3, Adrien Gibault5, Aurelie Jougla6, Frank Travers4, Gregoire P. Millet6, and Robin Candau7
1 Department of Anatomy and Physiology, University of Padova, Padova, Italy; School of Sport and Education, Brunel University, London, United Kingdom; Faculty of Sport Sciences, UMR 866 INRA, University of Montpellier I, Montpellier, France
2 Department of Anatomy and Physiology, University of Padova, Padova, Italy
3 Dpt STAPS, Universite d'Avignon, Laboratoire Physiologie des adaptations Cardio-vasculaires a l'exercice, AVIGNON, France
4 UMR 5236 CNRS, University of Montpellier I, Montpellier, France
5 Laboratoire Physiologie des adaptations Cardio-vasculaires a l'exercice, Dpt STAPS, Universite d'Avignon, Avignon, France
6 Faculty of Sport Sciences, UMR 866 INRA, University of Montpellier I, Montpellier, France
7 Faculty of Sport Sciences, UMR 866 INRA, University of Montpellier I, Montpellier, France; UMR 5236 CNRS, University of Montpellier I, Montpellier, France
* To whom correspondence should be addressed. E-mail: belle.roels{at}orioncro.com.
This study aimed to determine the changes in soleus myofibrillar ATPase (m-ATPase) activity and MHC isoform expression after endurance training and/or chronic hypoxic exposure. Dark Agouti rats were randomly divided into four groups: control, normoxic sedentary (N, n = 14); normoxic endurance trained (NT, n = 14); hypoxic sedentary (H, n = 10) and hypoxic endurance trained (HT, n = 14). Rats lived and trained in normoxia at 760 mmHg (N and NT), or hypobaric hypoxia at 550 mmHg (~ 2800 m) (H and HT). M-ATPase activity was measured by Rapid Flow Quench technique; myosin subunits were analyzed with mono- and two-dimensional gel electrophoresis. Endurance training significantly increased m-ATPase (P < 0.01), although an increase in MHC-I content occurred (P < 0.01). In spite of slow-to-fast transitions in MHC isoform distribution in chronic hypoxia (P < 0.05) no increase in m-ATPase was observed. The rate constants of m-ATPase were 0.0350 s-1 (SD 0.0023) and 0.047 s-1 (SD 0.0050) for N and NT and 0.033 s-1(SD 0.0021) and 0.038 s-1 (SD 0.0032) for H and HT. Thus, dissociation between variations in m-ATPase and changes in MHC isoform expression was observed. Changes in fraction of active myosin heads, in myosin light chain isoform (MLC) distribution or in MLC phosphorylation could not explain the variations in m-ATPase. Myosin post-translational modifications or changes in other myofibrillar proteins may therefore be responsible for the observed variations in m-ATPase activity.
