In vitro Na+,K+-ATPase (EC 3.6.1.3)-dependent respiration and protein synthesis in skeletal muscle of pigs fed at three dietary protein levels.

1. Eighteen pigs were offered diets containing 130, 170 or 210 g protein/kg with three barrows and three gifts per diet from 20 to 60 kg live weight. Oxygen consumption, Na+,K+-ATPase (EC 3.6.1.3)-dependent and -independent respiration and protein synthesis were measured in vitro in intercostal and sartorius muscle preparations from these pigs. 2. Increasing dietary protein concentration increased (P less than 0.01) daily gain and dissectible muscle in carcass. 3. O2 consumption and Na+,K+-ATPase-dependent respiration of the intercostal and sartorius muscles increased linearly (P less than 0.01) with increase in dietary protein concentration. The requirement for the support of the transport of Na+ and K+ across the cell membrane in these muscles, on average, accounted for 22-25% of the O2 consumption. 4. Synthesis rate (mg/g per d) of protein in the sartorius muscle increased (P less than 0.05) from 3.05 to 5.07 and increased (P less than 0.1) from 2.57 to 4.06 in the intercostal muscle as dietary protein increased from 130 to 210 g/kg diet. 5. Regression of Na+,K+-ATPase-dependent respiration against protein synthesis in each of intercostal and sartorius muscles showed a linear relation, an attestation of a close link between productive processes and auxiliary energy expenditure.