Combined effect of epinephrine and exercise on calpain/calpastatin and cathepsin B and L activity in porcine longissimus muscle

The objective of the study was to improve the understanding of the relation ship between the effect of epinephrine plus exercise and meat tenderness. T he calpain, calpastatin, and cathepsin B + L activities and postmortem prot eolysis in porcine longissimus muscle were studied. The muscle glycogen sto res were depleted in five pigs by s.c. injection of epinephrine (.3 mg/kg) at 15 h antemortem and exercise on a treadmill (5 min, 3.8 km/h) immediatel y before slaughter. Antemortem injection of epinephrine and treadmill exerc ise resulted in higher ultimate pH (6.32 vs 5.66 in control) and decreased (P < .05) thaw loss, cooking loss, and shear force values. The muscle energ y depletion treatment increased (P < .05) the muscle mu-calpain activity me asured 42 min postmortem, and at 24 h mu-calpain activity was still approxi mately 50% greater in the high ultimate pH group. Also, as the ratio of mu- calpain to calpastatin increased (P < .01), the overall proteolytic potenti al of the calpain system were greater. These observations suggest that the muscle energy level may influence the activity of the calpain system in the living animal. The high ultimate pH group showed lower (P < .001) cathepsi n B + L activity in the myofibrillar and the soluble fractions after 8 d of storage, suggesting that the increased ultimate pH increased the stability of the lysosomal membrane and thereby reduced the release of cathepsins fr om the lysosomes during storage. The SDS-PAGE showed increased (P < .001) d egradation of a 39-kDa band in. the epinephrine and exercise-treated sample s. Degradation products at 30, 31, and 32 kDa were labeled by troponin-T an tibody in western blot. An appearing 24-kDa band was identified as a tropon in-I degradation product in western blot. The proteolytic degradation patte rn of myofibrillar proteins during storage differed in control and treated samples, supporting the hypothesis that calpain-mediated proteolysis was af fected after treatment, resulting in meat with high ultimate pH.