The Role of Heat Shock Protein 70 in Protecting Muscle Mechanical Function & SERCA Function in Human Skeletal Muscle
Stewart, Riley David
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Two studies were conducted to determine if Hsp70 is able to protect human skeletal muscle from muscle mechanical damage and alterations in SERCA activity associated with prolonged concentric exercise. In the first study, one-legged isometric knee extension exercise at 40% MVC and a duty cycle of 50% (5 sec contraction followed by 5 sec of relaxation) was used to induce a heat shock response in one leg only. Participants were followed over six recovery days to determine the time course of Hsp70 induction and decay. Results showed fiber type specific increases in Hsp70 that persisted in one leg only throughout six days of recovery. These increases in Hsp70 occurred with only transient changes in Ca2+ uptake and muscular force. With the exception of minor decreases in low frequency force, there were no apparent reductions in muscular force or SERCA activity by the third recovery day. Therefore an exercise protocol was established which was able to induce a heat shock response with only minor alterations in muscle mechanical function and SERCA activity. In the second study, the same isometric exercise was employed, however, on the day corresponding to recovery day 3 in the first study, participants were asked to complete a one hour cycling protocol at 70% VO2 max. The goal was to cause similar one-legged increases in Hsp70 as the first study and to then challenge SERCA activity and muscular force in the presence of elevated Hsp70 by using cycling exercise. Results showed cycling induced reductions in maximal Ca2+ ATPase activity, muscular force, rates of muscle relaxation, and rates of muscle force development were attenuated by the preconditioning (isometric) exercise. These studies confirm the idea that preconditioning exercise is able to attenuate subsequent exercise induced insults to SERCA activity and muscular force, likely through an Hsp70 mediated mechanism.