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This Article Full Text Full Text (PDF) All Versions of this Article: 294/6/R1911    most recent 00210.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Roels, B. Articles by Candau, R. PubMed PubMed Citation Articles by Roels, B. Articles by Candau, R.

ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Paradoxical effects of endurance training and chronic hypoxia on myofibrillar ATPase activity

¹UMR 866 Institut National de la Recherche Agronomique, University of Montpellier I, Faculty of Sport Sciences, Montpellier, France; ²Department of Anatomy and Physiology, University of Padova, Padova, Italy; ³Brunel University, School of Sport and Education, West-London, UK; ⁴EA 2426 Laboratory of Cardiovascular Adaptations to Exercise, Avignon, France; ⁵UMR 5236 Centre National de la Recherche Scientifique, University of Montpellier I, France; and ⁶Department of Physics and Applied Mathematics, Faculty of Chemistry, University of Bucharest, Bucharest, Romania

Submitted 24 March 2006 ; accepted in final form 26 March 2008

This study aimed to determine the changes in soleus myofibrillar ATPase (m-ATPase) activity and myosin heavy chain (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 (2,800 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 ± 0.0023 s^–1 and 0.047 ± 0.0050 s^–1 for N and NT and 0.033 ± 0.0021 s^–1 and 0.038 ± 0.0032 s^–1 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 posttranslational modifications or changes in other myofibrillar proteins may therefore be responsible for the observed variations in m-ATPase activity.

myosin ATPase activity; myosin heavy chain isoform; myosin light; chain isoform; exercise; fast kinetics