Functional aspects of skeletal muscle contractile apparatus and sarcoplasmic reticulum after fatigue.
This study examined the effects of fatigue on the functional aspects of the contractile apparatus and sarcoplasmic reticulum (SR). Frog semitendinosus muscles were stimulated to fatigue, and skinned fibers or a homogenate fraction was prepared from both fatigued and rested contralateral muscles. In fatigued fibers, maximal Ca2+-activated force of the contractile apparatus was unaltered, whereas maximal actomyosin-ATPase activity was depressed by 20%. The Ca2+ sensitivity of force was increased, whereas that of actomyosin-ATPase was not altered. Also, the rate constant for tension redevelopment was decreased at submaximal Ca2+ concentration. These latter findings suggest that fatigue slows the dissociation of force-generating myosin cross bridges. Ca2+ uptake and Ca2+-ATPase activity of the SR were depressed by 46 and 21%, respectively, in the fatigued muscles. Fatigue also reduced the rates of SR Ca2+ release evoked by AgNO3 and 4-chloro-m-cresol by 38 and 45%, respectively. During fatigue, the contractile apparatus and SR undergo intrinsic functional alterations. These changes likely result in altered force production and energy consumption by the intact muscle.
Muscular Function Laboratory, Department of Human Nutrition, Foods, and Exercise, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0430, USA. jhwms@vt.edu
J H
JH
Williams
C W
CW
Ward
E E
EE
Spangenburg
R M
RM
Nelson
D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D004558:Electric Stimulation; D004734:Energy Metabolism / Q000502:physiology; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000201:enzymology / Q000502:physiology; D018482:Muscle, Skeletal / Q000201:enzymology / Q000502:physiology* / Q000648:ultrastructure; D011894:Rana pipiens; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000502:physiology*
D000252:Calcium-Transporting ATPases; D002118:Calcium