title: 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.
authors.affiliation: Nutrition, Metabolism, and Exercise Laboratory, DWR Department of Geriatrics, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA.
authors.forename: Chad C
authors.initials: CC
authors.lastname: Carroll
authors.forename: James D
authors.initials: JD
authors.lastname: Fluckey
authors.forename: Rick H
authors.initials: RH
authors.lastname: Williams
authors.forename: Dennis H
authors.initials: DH
authors.lastname: Sullivan
authors.forename: Todd A
authors.initials: TA
authors.lastname: Trappe
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D000596:Amino Acids / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D000601:Amino Acids, Essential / Q000097:blood; D001706:Biopsy; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D003903:Deuterium / Q000737:chemistry; D004573:Electrolytes; D005260:Female; D005947:Glucose; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000737:chemistry; D009124:Muscle Proteins / Q000032:analysis / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D009210:Myofibrils / Q000737:chemistry; D018995:Myosin Heavy Chains / Q000032:analysis; D057947:Parenteral Nutrition Solutions; D010649:Phenylalanine / Q000737:chemistry / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D014176:Protein Biosynthesis / Q000187:drug effects / Q000502:physiology; D020033:Protein Isoforms / Q000032:analysis / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000737:chemistry; D012996:Solutions
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000596:Amino Acids; D000601:Amino Acids, Essential; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D004573:Electrolytes; D009124:Muscle Proteins; D057947:Parenteral Nutrition Solutions; D010750:Phosphoproteins; D020033:Protein Isoforms; D012996:Solutions; C545824:amino-acid, glucose, and electrolyte solution; D010649:Phenylalanine; D003903:Deuterium; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D018995:Myosin Heavy Chains; D005947:Glucose