Morphological and biochemical assessment of apoptosis in different skeletal muscles of bulls during conditioning

Apoptosis is a form of cell death that involves the changes of mitochondrial function and the regulated activation of caspase cascades, which selectively cleave cytoskeleton proteins and catalyze the changes of cell organelles and morphological structure. The changes of mitochondrial function, cell morphological structure, and degradation of cytoskeleton are considered to be responsible for the development of meat qualities. The LM, semitendinosus, and psoas minor (PM) muscles of 5 crossbred bulls were used to observe the morphologic and quantitative changes of apoptosis, as well as the change of caspase-3 activity during 7 d storage. Transmission electron microscopy shows that the typical features of apoptosis appeared in muscles between d 1 and 4. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) positive nuclei were detected at d 4 and increased subsequently. The count of TUNEL-positive nuclei was different in 3 muscles at d 7 (P < 0.001). There was a significant increase in caspase-3 activities at 4 h postmortem relative to the activities at the first 30 min in 3 muscles (P = 0.0147 in LM; P = 0.0058 in PM; P = 0.0306 in semitendinosus), and the apexes had 2.9 to 6.5 times more activities than activities at the first 30 min postmortem. Apoptosis did exist in 3 types of muscles during the conditioning period. Apoptosis and caspase cascades system could be associated with the postmortem development of meat quality in skeletal muscles of bulls.