Ischemia-reperfusion-induced calpain activation and SERCA2a degradation are attenuated by exercise training and calpain inhibition

Department of Applied Physiology and Kinesiology, Center for Exercise Science, and Departments of Psychiatry and Neuroscience, Center for Traumatic Brain Injury Studies, University of Florida, Gainesville, Florida Submitted 13 July 2005 ; accepted in final form 7 September 2005 The Ca 2+ -activated protease calpain has been shown to play a deleterious role in the heart during ischemia-reperfusion (I/R). We tested the hypothesis that exercise training would minimize I/R-induced calpain activation and provide cardioprotection against I/R-induced injury. Hearts from adult male rats were isolated in a working heart preparation, and myocardial injury was induced with 25 min of global ischemia followed by 45 min of reperfusion. In sedentary control rats, I/R significantly increased calpain activity and impaired cardiac performance (cardiac work during reperfusion = 24% of baseline). Compared with sedentary animals, exercise training prevented the I/R-induced rise in calpain activity and improved cardiac work (recovery = 80% of baseline). Similar to exercise, pharmacological inhibition of calpain activity resulted in comparable cardioprotection against I/R injury (recovery = 86% of baseline). The exercise-induced protection against I/R-induced calpain activation was not due to altered myocardial protein levels of calpain or calpastatin. However, exercise training was associated with increased myocardial antioxidant enzyme activity (Mn-SOD, catalase) and a reduction in oxidative stress. Importantly, exercise training also prevented the I/R-induced degradation of sarco(endo)plasmic reticulum Ca 2+ -ATPase (SERCA)2a. These findings suggest that increases in endogenous antioxidants may diminish the free radical-mediated damage and/or degradation of Ca 2+ handling proteins (such as SERCA2a) typically observed after I/R. In conclusion, these results support the concept that calpain activation is an important component of I/R-induced injury and that exercise training provides cardioprotection against I/R injury, at least in part, by attenuating I/R-induced calpain activation. antioxidants; oxidative stress; cardioprotection Address for reprint requests and other correspondence: S. K. Powers, Dept. of Applied Physiology and Kinesiology, Center for Exercise Science, Univ. of Florida, Gainesville, FL 32611 (e-mail: spowers{at}hhp.ufl.edu )