Rat Gastrocnemius Skeletal Muscle Calpains And Calpastatin With Acute Exhaustive And Repeated Exercise Training

Calpains are intracellular nonlysosomal Ca²⁺-regulatedcysteine proteases. In vitro, they can degrade many cytoskeleton proteinsand contractile proteins. They involved in the skeletal muscle proteindegradation, life and death of the cell and cytoskeleton formation et al.Muscle tissue expresses mainly three different calpains: the ubiquitouscalpains (m-calpain andμ-calpain) and their endogenous inhibitor,calpastatin. Moreover, n-calpain is also mainly expressed in skeletalmuscle. The degradation of skeletal muscle protein increased after anunaccustomed exercise protocol, however, there are no evidencesavailable shown that exercise training of different duration may result in adifferent expression of calpains/calpastatin and their relationship withexercise-induced muscle injury. The objective of this study was toinvestigate whether skeletal muscleμ-calpain, m-calpain, n-calpain andcalpastatin associated with acute exhaustive and repeated exercisetraining in a time or training load-dependent manner, and their relationsto muscle injury. 128 rats were divided into 3 groups randomly,non-exercised control group, acute exhaustive (AEE) and repeated (RE)exercise group. Biopsies of acute exhaustive exercise rats were taken immediately, 2h, 6h, 12h, 24h, 48h and 72h post exercise respectively.The repeated exercise group was divided into large and moderate loadexercise, each exercised 3, 5, 7 and 9 weeks respectively. Gastrocnemiusof each subgroup was harvested after exercise training. Biopsies werestained with H&E to observe the inflammatory cells and muscle injury.We used RT-PCR to detect mRNA expression of calpains/calpastatin, andwestern blot to detect protein expression of calpains/calpastatin. Resultsshowed that different expression of inflammatory cells and muscle injurywas observed. An up-regulation of mRNA for calpastatin was also found,which was also reflected in an increase in protein content, n-calpainmRNA was down-regulated and so is protein content after exercisetraining, m-calpain andμ-calpain showed no changes in mRNAexpression with exercise, m-calpain activity increased with time, whereasμ-calpain activity decreased with time. The decrease ofμ-calpain activitywas earlier than that of n-calpain expression in AEE. The differentexpression of calpains and calpastatin observed after exercise suggestedthat they had different influences in exercise-induced muscle injury andthere must be some different mechanisms. We conferred that theincreased activity of m-calpain promoted muscle proteins degradation andmuscle injury, contrary to it, calpastatin may has a protective function onmuscle injury. The change ofμ-calpain activity was earlier than muscleinjury, and may be a predictor of muscle injury. We also predicted that the decrease of n-calpain expression might facilitate the repairing ofinjured skeletal muscle. Repeated exercise stimulated muscle adaptationsto exercise induced injury, and also m-calpain activity.