Hypoxia-induced fibre type transformation in rat hindlimb muscles. Histochemical and electro-mechanical changes.
Twelve male Sprague-Dawley rats (21 days old) were randomly assigned into two experimental groups: sea level control (CONT) and hypobaric hypoxia (HYPO). The HYPO rats were kept in an hypobaric chamber maintaining a simulated altitude of 4000 m (61.1 kPa). After 10 weeks of treatment, the rat hindlimb muscles [soleus (SOL) and extensor digitorum longus (EDL)] were subjected to histochemical and electro-mechanical analyses. Results indicated that compared to CONT the HYPO SOL muscle had a significantly greater relative distribution of fast-twitch-oxidative-glycolytic (FOG) fibres (28.9% SEM 2.0 vs 18.3% SEM 1.8, P less than 0.01) with a significant decrease in slow twitch oxidative fibre distribution (69.5% SEM 2.4 vs 82.9% SEM 3.1, P less than 0.01). Compared to CONT the HYPO EDL muscle also manifested a significant increase in FOG fibre distribution (51.6% SEM 0.8 vs 46.6% SEM 1.1, P less than 0.01), but this was accompanied by a significant decrease in fast twitch glucolytic fibres (44.3% SEM 0.9 vs 49.2% SEM 1.7, P less than 0.05). These histochemical fibre type transformations accompanied significant and expected changes in the electro-mechanical parameters tested in situ, e.g. maximal twitch force, maximal rate of force development, contraction time, half relaxation time, force: frequency curve, and fatigability. It was concluded that chronic hypobaric hypoxia could have a potent influence upon the phenotype expression of muscle fibres.
Itoh
K
K
Laboratory of Applied Physiology, College of Liberal Arts and Sciences, Kyoto University, Japan.
Moritani
T
T
Ishida
K
K
Hirofuji
C
C
Taguchi
S
S
Itoh
M
M
D000818:Animals; D001274:Atmospheric Pressure; D001696:Biomechanical Phenomena; D004594:Electrophysiology; D006614:Hindlimb; D006651:Histocytochemistry; D000860:Hypoxia / Q000209:etiology / Q000503:physiopathology*; D008297:Male; D009132:Muscles / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains