Human soleus and vastus lateralis muscle protein metabolism with an amino acid infusion

Abstract

The calf muscles, compared with the thigh, are less responsive to resistance exercise in ambulatory and bed-rested individuals, apparently due to muscle-specific differences in protein metabolism. We chose to evaluate the efficacy of using amino acids to elevate protein synthesis in the soleus, because amino acids have been shown to have a potent anabolic effect in the vastus lateralis. Mixed muscle protein synthesis in the soleus and vastus lateralis was measured before and after infusion of mixed amino acids in 10 individuals (28 +/- 1 yr). Phosphorylation of ribosomal protein p70 S6 kinase (p70S6K; Thr389) and eukaryotic initiation factor 4E-binding protein-1 (4E-BP1; Thr37/46) was also evaluated at rest and after 3 h of amino acid infusion. Basal protein synthesis was similar (P = 0.126), and amino acids stimulated protein synthesis to a similar extent (P = 0.004) in the vastus lateralis (0.043 +/- 0.011%/h) and soleus (0.032 +/- 0.017%/h). Phosphorylation of p70S6K (P = 0.443) and 4E-BP1 (P = 0.192) was not increased in either muscle; however, the soleus contained more total (P = 0.002) and phosphorylated (P = 0.013) 4E-BP1 than the vastus lateralis. These data support the need for further study of amino acid supplementation as a means to compensate for the reduced effectiveness of calf resistance exercise in ambulatory individuals and those exposed to extended periods of unloading. The greater 4E-BP1 in the soleus suggests that there is a muscle-specific distribution of general translational initiation machinery in human skeletal muscle.

The influence of acute resistance exercise on cyclooxygenase-1 and -2 activity and protein levels in human skeletal muscle

“…The meal contained 50% of the subject's estimated caloric need [1.5 times the subject's predicted resting metabolic rate (10)]. This type of diet control has been used previously in similar studies of skeletal muscle metabolism (5,7,39).…”

Muscle protein synthesis and gene expression during recovery from aerobic exercise in the fasted and fed states

“…A catheter was placed in an antecubital vein for infusion of the stable, isotopically labeled amino acid (Cambridge Isotopes, Andover, MA). The amino acid tracer ( 2 H5-phenylalanine) was dissolved in 0.9% saline, passed through a 0.2-m filter, and infused at a constant rate after an initial priming dose, as we have previously described (6,9,20). The stable isotope infusion was administered for five continuous hours to ensure that steady state tracer enrichment in the plasma and muscle was maintained.…”

“…2 H5]-phenylalanine enrichment (tracer to tracee) in muscle samples (ϳ20 mg) from the vastus lateralis, as we have previously described (6,9,20). All samples were analyzed using GC-MS (6890N GC coupled with 5973 inert MSD; Agilent Technologies, Wilmington, DE) in triplicate using electron impact ionization and selected ion monitoring of m/z 234 (mϩ0), 235 (mϩ1), 237 (mϩ3), and 239 (mϩ5), with mϩ0 representing the lowest molecular weight of the ion.…”

Determinants of Disuse-Induced Skeletal Muscle Atrophy: Exercise and Nutrition Countermeasures to Prevent Protein Loss

“…In addition, because the first two steps in BCAA catabolism are common to the three BCAAs (186) and are upregulated by increased plasma leucine concentrations (187), resulting in abnormally low levels of circulating isoleucine and valine (183,187), supplementation with leucine alone with the aim of preventing muscle protein loss during inactivity is not recommended. Continuous infusion of 10% Travasol, which contains the 9 essential plus 6 nonessential amino acids, has been reported to result in increased rates of mixed muscle protein synthesis in humans (188). Furthermore, infusion of essential amino acids suppresses muscle protein breakdown in hindlimb-immobilized rats (185).…”