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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Differential effects of repetitive activity on sarcoplasmic reticulum responses in rat muscles of different oxidative potential

Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada

Submitted 5 January 2005 ; accepted in final form 15 September 2005

We investigated the hypothesis that muscles of different oxidative potential would display differences in sarcoplasmic reticulum (SR) Ca²⁺ handling responses to repetitive contractile activity and recovery. Repetitive activity was induced in two muscles of high oxidative potential, namely, soleus (SOL) and red gastrocnemius (RG), and in white gastrocnemius (WG), a muscle of low oxidative potential, by stimulation in adult male rats. Measurements of SR properties, performed in crude homogenates, were made on control and stimulated muscles at the start of recovery (R0) and at 25 min of recovery (R25). Maximal Ca²⁺-ATPase activity (V_max, µmol·g protein^–1·min^–1) at R0 was lower in stimulated SOL (105 ± 9 vs. 135 ± 7) and RG (269 ± 22 vs. 317 ± 26) and higher (P < 0.05) in WG (795 ± 32 vs. 708 ± 34). At R25, V_max remained lower (P < 0.05) in SOL and RG but recovered in WG. Ca²⁺ uptake, measured at 2,000 nM, was depressed (P < 0.05) in SOL and RG by 34 and 13%, respectively, in stimulated muscles at R0 and remained depressed (P < 0.05) at R25. In contrast, Ca²⁺ uptake was elevated (P < 0.05) in stimulated WG at R0 by 9% and remained elevated (P < 0.05) at R25. Ca²⁺ release, unaltered in SOL and RG at both R0 and R25, was increased (P < 0.05) in stimulated WG at both R0 and R25. We conclude that SR Ca²⁺-handling responses to repetitive contractile activity and recovery are related to the oxidative potential of muscle.

skeletal muscles; contractile activity; calcium handling

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