Matched adaptations of electrophysiological, physiological, and histological properties of skeletal muscles in response to chronic hypoxia.
This study tried to differentiate the consequences of chronic hypoxia on the electrophysiological and physiological properties and the histological characteristics of slow and fast muscles in rats. Animals inhaled a 10% O(2) concentration for a 1-month period. Then, slow [soleus (SOL)] and fast [extensor digitorum longus (EDL)] muscles were analyzed in vitro by physiological and electrophysiological measurements and histological analyses. The results were compared to those obtained in corresponding muscles of an age-matched normoxic group. After exposure to hypoxia: (1) in SOL, there was a tendency to elevated F(max), a significant increase in twitch force and tetanic frequency and a shortening of M-wave duration, and a reduced percentage of type I fibres, whereas the proportion of type IIa fibres doubled; (2) in EDL, F(max) and tetanic frequency were lowered, the muscle became less resistant to fatigue, and the proportion of type IId/x fibres was halved. Then, after 1 month of hypoxia, in the SOL muscle, both the contractile and histological properties resemble those of a fast muscle. By contrast, the EDL became slower, despite its histology was modestly affected. Reduced muscle use in hypoxia could explain the tendency for deteriorating adaptations in EDL, and the faster properties of SOL could result from hypoxia-induced inhibition of the growth-related fast-to-slow shift in muscle fibre types.
Faucher
Marion
M
Laboratoire de Physiopathologie Respiratoire, Institut Jean Roche, Faculté de Médecine, Université de la Méditerranée, Bd Pierre Dramard, 13916 Marseille cedex, France. jammes.y@jean-roche.univ-mrs.fr
Guillot
Chantal
C
Marqueste
Tanguy
T
Kipson
Nathalie
N
Mayet-Sornay
Marie-Hélène
MH
Desplanches
Dominique
D
Jammes
Yves
Y
Badier
Monique
M
D000222:Adaptation, Physiological; D000818:Animals; D006651:Histocytochemistry; D000860:Hypoxia / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000473:pathology / Q000503:physiopathology*; D009218:Myosins / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley
D009218:Myosins