The effect of nutritional status on protein degradation and components of the calpain system in skeletal muscle of weaned wether lambs

The association between the rate of protein degradation and the components of the calpain system in lambs fed at sub-maintenance, maintenance and supra-maintenance levels of nutrition was investigated. Weights of the cold carcass, liver, kidney, pluck and m. semitendinosus increased with nutritional level (P<0·05). The rate of protein degradation in the hind-limb was determined using an in vivo arterio-venous method. Blood flow, protein gain and protein synthesis across the hind-limb increased with nutritional status (P<0·05). There was an increase in the amount of protein synthesised per unit of RNA (mg RNA/g protein) with improved nutritional status. The rate of protein degradation across the hind-limb increased between the sub-maintenance and maintenance treatments (P<0·05) but there was no further increase above maintenance (P>0·10). The activity of the components of the calpain system was determined after separation on a DEAE-Sepharose column with a stepwise gradient with increasing NaCl concentrations. Although there were no significant effects of nutritional status on the components of the calpain system, there was a negative association between the rate of protein degradation and the activity of μ-calpain (R2=0·61; P<0·005) and a weak positive association between calpastatin activity and protein gain (R2=0·44; P<0·05).