PROTEIN DEGRADATION IN EXERCISED SKELETAL MUSCLE: ROLE OF CALCIUM ACTIVATED FACTOR

ANN CATHERINE SNYDER, Purdue University

Abstract

Strenous exercise is associated with ultrastructural disturbances in muscle, increased muscle inflammation and accelerated muscle protein degradation. The precise myofibrillar proteins affected and the mechanism of exercise-induced protein degradation are unknown. Therefore, the purpose of this study was threefold: (1) to confirm that eccentric exercise does increase muscle protein degradation, (2) to determine if alterations in myofibrillar proteins occur after exercise and (3) to determine if enhanced protein degradation is associated with increased activity of a specific protease, the calcium activated factor (CAF). Methods. Untrained rats (n = 60) were randomly assigned to one of three treatment groups: (1) sedentary (SED), (2) exercised and sacrificed 18 hr later (EX18) and (3) exercised and sacrificed 42 hr later (EX42). The exercised animals ran for 90 min on a treadmill at 16 m/min with a 16 degree decline. This exercise regimen involved eccentric contractions of the triceps brachii muscles. Muscle protein degradation was determined by analysis of urinary 3-methylhistidine (3MHIS). The relative percentages of the minor myofibrillar proteins were determined electrophoretically with the use of sodium dodecyl sulfate-polyacrylamide gels. The amount of CAF was determined by first isolating CAF and then measuring its activity against casein. Results. Muscle protein degradation increased after the non-exhaustive eccentric exercise. Elevated levels of 3MHIS were observed in the urine 18 and 42 hrs after the exercise bout, but were significant (P < .05) only after 42 hrs. The increased muscle degradation was associated with a significant increase in the relative percentage of a minor myofibrillar protein weighing 125,000 D. This unknown protein was found in small amounts in the SED and EX18 groups muscles, but was 2.4-fold greater in the muscles from the EX18 group (P < .05). Of the other minor myofibrillar proteins, small increases and decreases were observed, but none of these changes was statistically significant. CAF protease activity was not significantly different among treatment groups. Conclusions. After eccentric exercise, muscle protein degradation is increased, and there are changes in the electrophoretic distribution of the minor myofibrillar proteins. However, our data do not provide conclusive support for CAF involvement in these changes.

Degree

Ph.D.

Subject Area

Anatomy & physiology|Animals

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