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

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2008-06, Vol.294 (6), p.R1911-R1918
• Main Authors: Roels, B, Reggiani, C, Reboul, C, Lionne, C, Iorga, B, Obert, P, Tanguy, S, Gibault, A, Jougla, A, Travers, F, Millet, G. P, Candau, R
• Format: Article
• Language: English
• Subjects: Adenosine triphosphatase; Adenosine Triphosphatases; Adenosine Triphosphatases - metabolism; Animals; Anoxia; Body Weight; Body Weight - physiology; Calcium; Calcium - metabolism; Cellular Biology; Exercise; Hypoxia; Hypoxia - physiopathology; Life Sciences; Male; Muscle, Skeletal; Muscle, Skeletal - enzymology; Myofibrils; Myofibrils - enzymology; Myosin Heavy Chains; Myosin Heavy Chains - metabolism; Physical Conditioning, Animal; Physical Conditioning, Animal - physiology; Physical Endurance; Physical Endurance - physiology; Proteins; Rats; Rats, Inbred Strains; Rodents; Studies
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00210.2006

1 UMR 866 Institut National de la Recherche Agronomique, University of Montpellier I, Faculty of Sport Sciences, Montpellier, France; 2 Department of Anatomy and Physiology, University of Padova, Padova, Italy; 3 Brunel University, School of Sport and Education, West-London, UK; 4 EA 2426 Laboratory of Cardiovascular Adaptations to Exercise, Avignon, France; 5 UMR 5236 Centre National de la Recherche Scientifique, University of Montpellier I, France; and 6 Department 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 Address for reprint requests and other correspondence: B. Roels, Orion Clinical Services, 7 Bath Rd., Slough, Berkshire SL1 3UE UK (e-mail: belleroels{at}hotmail.com )