Issn Print: 0195-9131
Publication Date: 2001/05/01
KINETICS OF METABOLIC ACTIVATION IN CANINE MUSCLE IN SITU AT THE ONSET OF HIGH INTENSITY CONTRACTIONS
K M. Kelley; R A. Howlett; L B. Gladden; B Grassi; M C. Hogan
+ Author Information
Author Information: Dept. Medicine, Univ. California, San Diego, La Jolla, CA 92093
Excerpt
The purpose of this study was to characterize the activation of ATP generating pathways in canine skeletal muscle during the first min of a 3 min bout of intense exercise. The gastrocnemius muscle (n = 6) was surgically isolated in anesthetized dogs and the tendon was attached to a force transducer. Isometric tetanic muscle contractions (0.2 msec stimuli for 200 msec duration at 50 Hz, one per sec) were elicited via the sciatic nerve. Muscle biopsies were taken at 10, 20, 30, 45, 60, and 180 sec in the exercise bout. Blood samples were taken at 15, 30, 60, and 180 sec. Muscle force production and venous blood flow were recorded continuously (100 Hz) throughout the exercise bout. Muscle oxygen consumption had increased to 34% of the peak VO2 (VO2 at 180 sec) by 15 sec, and had reached 81% of peak VO2 by 60 sec. During the first 15 sec of contractions, PCr decreased by 10% from resting values, by 33% at 30 sec, and by 45% at 60 sec. By comparison, net lactate output from the muscle had risen 4-fold by 15 sec and 10-fold by 30 sec. The rapid increase in oxygen consumption and lactate output during the first 15–30 sec of contractions suggests that ATP generating pathways other than PCr hydrolysis are activated more rapidly than previously believed, and may in fact provide a significant portion of the ATP required at the start of intense bouts of exercise.
Supported by NIH Grant No. AR-40342, AR-40155, NATO CRG 972111, and NSERC (Canada).
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