Abstract
The purpose of this study was to investigate changes in sarcoplasmic reticulum (SR) Ca2+-sequestering capacity in rat fast-twitch plantaris (PL) and slow-twitch soleus (SOL) muscles during recovery after high-intensity exercise. The rats were subjected to treadmill runs to exhaustion at the intensity (10% incline at 50 m/min) estimated to require 100% of maximal O2 consumption. The muscles were excised immediately after exercise, and 15, 30 and 60 min after exercise. Acute high-intensity exercise evoked a 27 % and 38 % depression (P<0.05) in SR Ca2+-uptake rate in the PL and SOL, respectively. In the PL, uptake rate remained lower (P<0.05) at 30 min of recovery but recovered 60 min after exercise. These alterations were paralleled by those of SR Ca2+-ATPase activity. On the other hand, SR Ca2+-uptake rate in the SOL recovered 15 min after exercise. Unlike the PL, discordant time-course changes between SR Ca2+-ATPase activity and uptake occurred in the SOL during recovery. SR Ca2+-ATPase activities were unaltered with exercise and elevated (P<0.05) by 25, 30 and 30% at 15, 30 and 60 min of recovery, respectively. These results demonstrate that SR Ca2+-sequestering ability is restored faster in slow-twitch than in fast-twitch muscle during recovery periods following a single bout of high-intensity exercise and suggest that the rapid restoration of SR Ca2+-sequestering ability in slow-twitch muscle could contribute to inhibition of disturbances in contractile and structural properties that are known to occur with raised myoplasmic Ca2+ concentrations.
