In vitro energy costs of Na+, K+ATPase activity and protein synthesis in muscle from calves differing in age and breed.

1. An in vitro preparation was used to measure rates of oxygen consumption, Na+, K+-ATPase-dependent respiration. [14C]phenylalanine incorporation and tyrosine release of skeletal (sternomandibularis) muscle from 10-21-d-old (three) and 7-month dairy (three) calves and control (CDM; four) and extreme double-muscled (EDM; two) calves. 2. Rates of oxygen consumption was greatest (P less than 0.001) for muscle from 10-21-d-old dairy calves and lowest (P less than 0.05) for CDM calves. 3. Ouabain (10(-6) M) caused a 40% inhibition of muscle respiration. 4. Na+, K+-ATPase-independent respiration was similar for muscle from all calf groups except 10-21-d-old dairy calves which had a value 26% greater (P less than 0.001) than than of older dairy calves. 5. Na+, K+-ATPase-independent respiration was 16% greater (P less than 0.001) for muscle from 10-21-d-old than that of older dairy calves while muscle from EDM calves had a value 11% greater than that of CDM calves. 6. The rate of [14C]phenylalanine incorporation was greater (P less than 0.05) for muscle from 10-21-d-old dairy than from older dairy calves, similar between older dairy and CDM calves, and decreased (P less than 0.05) for EDM calves. 7. Rate of tyrosine release was greatest (P less than 0.05) for muscle from CDM and EDM calves; both dairy groups had similarly low rates of muscle tyrosine release. 8. The energy estimated to be required for peptide bond synthesis accounted for 2.0-3.3% of the O2 consumption of the muscle preparations.