Stretch-activated ion channel blockade attenuates adaptations to eccentric exercise.
OBJECTIVE
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.


CONCLUSIONS
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.
Butterfield
Timothy A
TA
Division of Athletic Training, Department of Rehabilitation Sciences, College of Health Sciences, University of Kentucky, Lexington, KY, USA. tim.butterfield@uky.edu
Best
Thomas M
TM
D000818:Animals; D007473:Ion Channels / Q000037:antagonists & inhibitors*; D007537:Isometric Contraction / Q000187:drug effects*; D018763:Muscle Fatigue / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000187:drug effects*; D010805:Physical Conditioning, Animal / Q000502:physiology; D011817:Rabbits; D012508:Sarcolemma / Q000187:drug effects*; D013307:Streptomycin / Q000494:pharmacology*
D007473:Ion Channels; D013307:Streptomycin