Uptake of 3H-leucine into different fractions of rat skeletal muscle following acute endurance and sprint exercise.

In order to study the specificity of the protein synthetic response to different acute exercise loads, 48 male rats served as non-exercised controls or ran at either 0.5 m . s-1 for 1 h or 1.5 m . s-1, 10 s: 20 s work : rest, for 1 h. Animals were killed and red and white vastus muscles excised from the controls or at 0, 2, 18, 24, or 48 h post-exercise. Muscle slices were incubated in a medium containing 10 muCi L-[4,5-3H]leucine for 30 min. Incorporation of the radionuclide was measured by liquid scintillation (dpm . mg-1 protein) in the whole homogenate and in four subcellular fractions. The endurance exercise elicited increased uptakes into the mitochondrial fractions of both red and white vastus at 2 and 18 h respectively. However, the mitochondrial uptake was depressed at 24 h in the red and at 2 h in the white vastus. Only in red vastus was incorporation into the soluble protein elevated following endurance exercise. The sprint protocol elicited increased uptake into soluble protein at 2 and 18 h in both red and white vastus and into mitochondrial protein at 18 and 24 h in the white vastus. The shifts in uptake in white vastus occurred in conjunction with depressed uptakes in the total homogenate. These data indicate that both the changes in the type of protein and the time course of amino acid incorporation following acute exercise are related to both the metabolic characteristics of the muscle fibers and the intensity of the exercise.