The calpain system in three muscles of normal and callipyge sheep

Activities of mu- and m-calpain and of calpastatin were measured at four di fferent times during postmortem storage (0, 1, 3, and 10 d) in three muscle s from either callipyge or noncallipyge (normal) sheep. The weights of two muscles, the biceps femoris and the longissimus, are greater in the callipy ge phenotype, whereas the weight of the infraspinatus is not affected. The activity of m-calpain was greater (P < 0.05) in the biceps femoris and long issimus from callipyge than in those from normal sheep, but it was the same in the infraspinatus in the two phenotypes. The extractable activity of m- calpain did not change (biceps femoris and infraspinatus) or decreased slig htly (longissimus) during postmortem storage. Extractable activity of <mu>- calpain decreased to zero or nearly zero after 10 d postmortem in all muscl es from both groups of sheep. The rate of decrease in CL-calpain activity w as the same in muscles from the callipyge and normal sheep. At all time poi nts during postmortem storage, calpastatin activity was greater (P < 0.05) in the biceps femoris and longissimus from the callipyge than from the norm al sheep, but it was the same in the infraspinatus from callipyge and norma l sheep. Calpastatin activity decreased (P < 0.05) in all three muscles fro m both phenotypes during postmortem storage; the rate of this decrease in t he callipyge biceps femoris and longissimus and in the infraspinatus from b oth the callipyge and normal sheep was slow, especially after the first 24 h postmortem, whereas calpastatin activity in the biceps femoris and longis simus from the normal sheep decreased rapidly. During postmortem storage, t he 125-kDa calpastatin polypeptide was degraded, but the 80-kDa subunit of mu -calpain was cleaved only to 76- and 78-kDa polypeptides even though ext ractable mu -calpain activity declined nearly to zero. Approximately 50 to 60% of total mu -calpain became associated with the nonextractable pellet a fter 1 d postmortem. The myofibril fragmentation index for the biceps femor is and longissimus from normal sheep increased significantly during postmor tem storage. The fragmentation index for the infraspinatus from the callipy ge and normal sheep increased to an intermediate extent, whereas the index for the biceps femoris and longissimus from the callipyge did not change du ring 10-d postmortem storage. The results suggest that postmortem tenderiza tion is related to the rate of calpastatin degradation in postmortem muscle and that calpastatin inhibition of the calpains in postmortem muscle is mo dulated in some as yet unknown manner.