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1Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de Mexico, México City 04510, México; 2Department of Physiology, School of Medicine, University of Maryland, Baltimore, Maryland 21201; 3Department of Physics E22 (Biophysics), Technical University of Munich, 80333 Garching, Germany; and 4Departamento de Bioquímica, Instituto Nacional de Perinatología, México City 11000, México
Submitted 25 August 2003 ; accepted in final form 10 March 2004
The sarcoplasmic reticulum (SR) Ca2+ pump is the main homeostatic regulatory mechanism in fast skeletal muscle that maintains intracellular Ca2+ concentration ([Ca2+]i) at the nanomolar level at rest. The transverse tubule (TT) Ca2+ pump transports cytosolic Ca2+ to the extracellular space. During prolonged muscular activity, [Ca2+]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 Ca2+ pumps of fast skeletal muscle from rabbit at rest. The Ca2+ 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 Ca2+ pump and 2) a significant change in the transition temperature of the SR Ca2+ pump Ca2+-binding domain. We conclude that the TT Ca2+ pump activity was upgraded in association with structural changes to handle the changes in [Ca2+]i and TT lumen Ca2+ concentration that occur during endurance exercise.
muscle adaptation; exercise training
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