Composition and turnover of contractile proteins in volume-overtrained skeletal muscle.
The purpose of this study was to find the composition shift of myosin heavy chain (MyHC) isoforms in overtraining in fast- and slow-twitch skeletal muscles and different changes in MyHC isofom composition, synthesis and turnover rate between 4-week and 6-week overtraining. Male Wistar rats were randomly assigned to 4-week and 6-week endurance training, 4-week and 6-week overtraining groups. Plantaris (Pla), extensor digitorum longus (EDL), and soleus (Sol) muscles were studied. Daily excretion of 3-methylhistidine (3-MeHis) pool as an indicator for protein degradation increased in the 4-week and 6-week overtraining group to 4.04 +/- 0.21 and 4.32 +/- 0.23 %/day subsequently in comparison with the control group (2.16 +/- 14 %/day, p < 0.001). In Pla muscle MyHC I isoform synthesis rate was 33 200 +/- 2150 (after 6-week overtraining 27 100 +/- 1800, p < 0.05), IIa 32 600 +/- 2100; IId 27 300 +/- 1890 and IIb isoform 20 100 +/- 1600 (after 6-week overtraining 15 500 +/- 1400, p < 0.05) dpm/M leucine/min. Actin synthesis rate increased in fast-twitch muscles during 4- and 6-week overtraining, and in soleus muscle during 6-week overtraining. In EDL and Sol muscle MyHC isoform composition during 6-week overtraining did not change significantly. During the 6-week overtraining the relative content of MyHC I and IIb isoforms decreased and IIa and IId isoforms increased in Pla muscle. The initial increase of MyHC IIb isoform after 4-week overtraining shows the higher stability of this isoform in comparison with MyHC I isoform in fast-twitch muscles during high volume exercise.
Seene
T
T
Department of Functional Morphology, University of Tartu, Tartu, Estonia. teet.seene@ut.ee
Kaasik
P
P
Alev
K
K
Pehme
A
A
Riso
E M
EM
D000818:Animals; D003285:Contractile Proteins / Q000032:analysis / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000032:analysis / Q000378:metabolism*; D010807:Physical Endurance / Q000502:physiology; D020033:Protein Isoforms / Q000032:analysis / Q000378:metabolism; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D012420:Running / Q000502:physiology*; D013997:Time Factors
D003285:Contractile Proteins; D020033:Protein Isoforms; D018995:Myosin Heavy Chains