Purpose: The purpose of this study was to test the hypothesis that stretch-activated ion channel (SAC) function is essential for the repeated bout effect (RBE) in skeletal muscle. Specifically, we investigated if daily injections of streptomycin (a known SAC blocker) would abrogate the muscle's adaptive resistance to the damaging effects of eccentric exercise over a 4-wk period. Furthermore, we hypothesized that the lack of an RBE would be due to the lack of functional adaptations that typically result from repeated bouts of eccentric exercise, including increased peak isometric torque, muscle hypertrophy, and rightward shift of the torque-angle relationship.
Methods: Twelve New Zealand white rabbits were each subjected to 12 bouts of eccentric exercise over a 4-wk period while receiving either daily injections of streptomycin or sham injections.
Results: Although blocking the SAC function completely eliminated the expected adaptive response in biomechanical parameters during the exercise regimen, there remained evidence of an acquired RBE, albeit with an attenuated response when compared with the muscles with intact SAC function.
Conclusion: Blocking sarcolemmal SAC eliminates functional adaptations of muscle after eccentric exercise. In the absence of SAC function, muscles subjected to chronic eccentric exercise still exhibit some degree of the RBE. As such, it appears that the signaling cascade that results in functional, biomechanical adaptations associated with the RBE during eccentric exercise is dependent upon intact SAC function.
1Division of Athletic Training, Department of Rehabilitation Sciences, College of Health Sciences, University of Kentucky, Lexington, KY; and 2Division of Sports Medicine, Department of Family Medicine, The OSU Sports Medicine Center, College of Medicine and Public Health, The Ohio State University, Columbus, OH
Address for correspondence: Timothy A. Butterfield, Ph.D., Department of Rehabilitation Sciences, College of Health Sciences, University of Kentucky, 900 South Limestone, Lexington, KY; E-mail: firstname.lastname@example.org.
Submitted for publication March 2008.
Accepted for publication July 2008.