Postmortem Proteolysis Is Not Driven by Calpain Alone: Epinephrine and Electrical Stimulation Reveal Multilevel Control

Abstract

To better understand how pH decline can alter calpain-1 autolysis , electrical stimulation (ES) and pre-slaughter epinephrine administration were used to alter pH decline. A total of 21 steers were fed for either 60 or 120 days and assigned to one of two injection treatments: saline at 48 and 24 h pre harvest (Con) or epinephrine (0.06 mg/kg) administered at 48 and 24 h pre harvest (Epi). Muscle samples were collected pre and post ES (45 min) at 1, 3, 6, 9, 24 hrs, 3 d, 5, 7, 10 and 14 d postmortem. Epinephrine elevated muscle pH from 24 h to 14 d at both feeding durations. High ultimate pH did not alter calpain 1 autolysis (P > 0.05). Epinephrine treated carcasses delayed calpastatin and desmin degradation under high pH conditions (P < 0.05). Electrical stimulation accelerated early pH decline (P < 0.05). Cattle fed 60 d had increased autolysis with no difference in desmin degradation (P = 0.0573; P > 0.05). While cattle fed for 120 days showed no difference in calpastatin degradation, ES reduced desmin degradation in con carcasses (P > 0.05; P < 0.0001). Longer time on feed showed a delayed calpastatin and desmin degradation and an increase in calpain-1 activation. Overall, calpain-1 autolysis alone does not translate into proteolysis.