A comparative analysis of the effects of exercise training on contractile responses in fast- and slow-twitch rat skeletal muscles.
The effects of 5 weeks treadmill-exercise training on isometric tension and contractile proteins were studied in intact and skinned isolated small bundles of rat skeletal soleus and extensor digitorum longus (edl) fibers. In soleus and edl muscles, 5 weeks exercise training: (i) increased twitch amplitude by 25% and 8%, respectively, without modification in the time-to-peak tension and the time constant of relaxation, (ii) increased the amplitude of K(+) contracture by 93% and 88%, respectively, and accelerated its relaxation by 17% and 43%, respectively, and (iii) increased the amplitude of caffeine contractures (soleus: 0.5 mM: 86%, 10 mM: 77%; edl: 0.5 mM: 89%, 10 mM: 87%). In conclusion, changes in contractile responses were associated with shifts in the steady state inactivation curves and in the voltage-dependent activation curve to a more negative potential, with increases in soleus and edl caffeine sensitivity, without changes in the Ca(2+) sensitivity of contractile proteins and myosin heavy chain isoforms.
Joumaa
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Laboratoire de Physiologie Générale, CNRS UMR 6018, Université de Nantes - Faculté des Sciences et des Techniques, F-44322 Nantes, France. claude.leoty@svt.univ-nantes.fr
Léoty
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C
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000737:chemistry / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000737:chemistry / Q000502:physiology*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000032:analysis; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
D010726:Phosphodiesterase Inhibitors; D002110:Caffeine; D018995:Myosin Heavy Chains; D011188:Potassium