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

Belle Roels (1, 2, 3) , Carlo Reggiani (1) , Cyril Reboul (4) , Corinne Lionne (5) , B. Iorga (5) , Philippe Obert (4) , Stéphane Tanguy (4) , A. Gibault (4) , A. Jougla (2) , F. Travers (5) , Gaëlle P. Millet (2) , R. Candau (2, 5)

1 Department of Human Anatomy and Physiology
2 Laboratoire Sport Performance Santé
3 School of Sport and Education
4 Physiopathologie des adaptations cardiovasculaires à l'Exercice
5 IRIM - Institut de Recherche en Infectiologie de Montpellier

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 (approximately 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.

Mots clés: myosin ATPase activity; myosin heavy chain isoform; myosin light; chain isoform; exercise; fast kinetics

Domaines: Biologie cellulaire

Belle Roels, Carlo Reggiani, Cyril Reboul, Corinne Lionne, B. Iorga, et al.. Paradoxical effects of endurance training and chronic hypoxia on myofibrillar ATPase activity.. AJP - Regulatory, Integrative and Comparative Physiology, 2008, 294 (6), pp.R1911-8. ⟨10.1152/ajpregu.00210.2006⟩. ⟨hal-00311705⟩