Effect of endurance exercise on the Ca2+ pumps from transverse tubule and sarcoplasmic reticulum of rabbit skeletal muscle.

The sarcoplasmic reticulum (SR) Ca(2+) pump is the main homeostatic regulatory mechanism in fast skeletal muscle that maintains intracellular Ca(2+) concentration (Ca(2+)](i)) at the nanomolar level at rest. The transverse tubule (TT) Ca(2+) pump transports cytosolic Ca(2+) to the extracellular space. During prolonged muscular activity, Ca(2+)](i) may increase. TT and SR isolated microsomal vesicles were highly purified, and the purity was checked by immunoblotting. The present study shows the effects of endurance exercise on the activities and structures of the TT and SR Ca(2+) pumps of fast skeletal muscle from rabbit at rest. The Ca(2+) pump activity increased manifolds in TT but did not change in SR. The protein denaturalization profiles obtained by differential scanning calorimetry showed 1) a shift in the transition temperature and an increase in the enthalpy of the TT Ca(2+) pump and 2) a significant change in the transition temperature of the SR Ca(2+) pump Ca(2+)-binding domain. We conclude that the TT Ca(2+) pump activity was upgraded in association with structural changes to handle the changes in Ca(2+)](i) and TT lumen Ca(2+) concentration that occur during endurance exercise.