Effects of varied fatigue protocols on sarcoplasmic reticulum calcium uptake and release rates.
The purpose of this investigation was to examine changes in sarcoplasmic reticulum (SR) function in muscles subjected to different patterns of muscle activity. Frog sartorius muscles were stimulated with tetanic trains (100 ms, 100 Hz) delivered at rates of 2.0, 0.5, and 0.2 trains/s. In one set of experiments, stimulation was continued until force had declined to approximately 17% of initial (constant fatigue), whereas in the other set, stimulation was continued for 1 min (constant duration). In the constant-fatigue experiments, Ca2+ uptake (1 mM MgATP) and release rates (25 microM AgNO3, 5 mM 4-chloro-m-cresol) were depressed by similar extents following each protocol. This occurred despite 1, 4, and 17 min of stimulation, respectively, used to induce fatigue. In the constant-duration experiments, larger reductions in SR function occurred following the highest frequency stimulation protocol. These data suggest that when muscles are fatigued to similar extents, depressions in SR function are independent of the activity protocol. On the other hand, when a constant duration of activity is imposed, changes in SR function are closely linked to the extent of force reduction.
Ward
C W
CW
Muscular Function Laboratory, Department of Human Nutrition, Foods and Exercise, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
Spangenburg
E E
EE
Diss
L M
LM
Williams
J H
JH
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003408:Cresols / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D004558:Electric Stimulation; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008297:Male; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000502:physiology*; D011894:Rana pipiens; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D012835:Silver Nitrate / Q000494:pharmacology; D019810:Sodium Azide / Q000494:pharmacology
D003408:Cresols; D007211:Indoles; C006984:chlorocresol; D000255:Adenosine Triphosphate; D012835:Silver Nitrate; D019810:Sodium Azide; D002118:Calcium; D004229:Dithiothreitol; C000543:cyclopiazonic acid