Protein Degradation in Human Skeletal Muscle Tissue: The Effect of Insulin, Leucine, Amino Acids and Ions

1981 ◽  
Vol 60 (3) ◽  
pp. 319-326 ◽  
Author(s):  
K. Lundholm ◽  
S. Edström ◽  
L. Ekman ◽  
I. Karlberg ◽  
P. Walker ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Protein Degradation ◽  
Muscle Tissue ◽  
Human Skeletal Muscle ◽  
Degradation Rate ◽  
Rectus Abdominus ◽  
Protein Degradation Rate

1. The protein degradation rate of human skeletal muscle was evaluated in vitro in isolated fibre bundles from the rectus abdominus muscle by measuring the tyrosine released from muscle tissue proteins. Protein metabolism in this semi-intact preparation was compared with that of the intact extensor digitorum longus muscles from rats under the same experimental conditions. 2. Protein balance was negative in both preparations, but protein synthesis and degradation were two to three times higher in the rat muscles. Tyrosine was released at a constant rate for at least 3 h of incubation independent of whether protein synthesis was inhibited or not. Disintegration of the muscle fibres more than doubled the tyrosine release rate. Human red gastrocnemius muscle showed 37% higher degradation rate compared with the predominantly white rectus abdominus muscle. The half-life of human skeletal muscle protein in vitro was estimated to be 20 days when calculated from the rate of tyrosine release. 3. The addition of leucine to the incubation medium decreased the rate of protein degradation, which was further decreased by the addition of other amino acids. Insulin did not influence the protein degradation rate during 2 h of incubation. This did not reflect a lack of sensitivity to insulin of the preparation, since protein synthesis responded to insulin. Calcium (5 mmol/l) stimulated and zinc (0.1 mmol/l) inhibited the protein degradation. 4. This experimental system may be suitable as an additional tool for evaluating protein degradation in human skeletal muscles.

Protein Synthesis in Isolated Human Skeletal Muscle Tissue: Evaluation of an Experimental Model

1979 ◽  
Vol 57 (2) ◽  
pp. 221-223 ◽  
Author(s):  
K. Lundholm ◽  
T. Scherstén
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Experimental Model ◽  
Muscle Tissue ◽  
Time Course ◽  
Human Skeletal Muscle ◽  
Skeletal Muscle Tissue ◽  
Muscle Fibres ◽  
Skeletal Muscle Fibres

Amino acids were incorporated into soluble proteins, myosin and myoglobin at constant rates for at least 4 h on incubation of isolated human skeletal muscle fibres. The time course of incorporation of leucine into proteins not attached to ribosomes was approximately constant, suggesting a continuous termination of proteins. A comparison between estimated pool size of ribosomes and incorporation rate of leucine into proteins indicated that initiation of peptides occurred even in the absence of insulin.

scholarly journals Identification in skeletal muscle of a distinct extracellular pool of amino acids, and its role in protein synthesis

1971 ◽  
Vol 121 (5) ◽  
pp. 817-827 ◽  
Author(s):  
R. C. Hider ◽  
E. B. Fern ◽  
D. R. London
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Incubation Medium ◽  
Extensor Digitorum Longus ◽  
Extensor Digitorum ◽  
Longus Muscle ◽  
Kinetics Of

1. The kinetics of radioactive labelling of extra- and intra-cellular amino acid pools and protein of the extensor digitorum longus muscle were studied after incubations with radioactive amino acids in vitro. 2. The results indicated that an extracellular pool could be defined, the contents of which were different from those of the incubation medium. 3. It was concluded that amino acids from the extracellular pool, as defined in this study, were incorporated directly into protein.

Leucine and insulin activate p70 S6 kinase through different pathways in human skeletal muscle

2001 ◽  
Vol 281 (3) ◽  
pp. E466-E471 ◽  
Author(s):  
Jeffrey S. Greiwe ◽  
Guim Kwon ◽  
Michael L. McDaniel ◽  
Clay F. Semenkovich
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Human Skeletal Muscle ◽  
Vastus Lateralis ◽  
S6 Kinase ◽  
Signaling Mechanism ◽  
Insulin Resistant ◽  
Branched Chain ◽  
Plasma Leucine

Amino acids and insulin have anabolic effects in skeletal muscle, but the mechanisms are poorly understood. To test the hypothesis that leucine and insulin stimulate translation initiation in human skeletal muscle by phosphorylating 70-kDa ribosomal protein S6 kinase (p70S6k), we infused healthy adults with leucine alone ( n = 6), insulin alone ( n= 6), or both leucine and insulin ( n = 6) for 2 h. p70S6k and protein kinase B (PKB) serine473phosphorylation were measured in vastus lateralis muscles. Plasma leucine increased from ∼116 to 343 μmol/l during the leucine-alone and leucine + insulin infusions. Plasma insulin increased to ∼400 pmol/l during the insulin-alone and leucine + insulin infusions and was unchanged during the leucine-alone infusion. Phosphorylation of p70S6k increased 4-fold in response to leucine alone, 8-fold in response to insulin alone, and 18-fold after the leucine + insulin infusion. Insulin-alone and leucine + insulin infusions increased PKB phosphorylation, but leucine alone had no effect. These results show that physiological concentrations of leucine and insulin activate a key mediator of protein synthesis in human skeletal muscle. They suggest that leucine stimulates protein synthesis through a nutrient signaling mechanism independent of insulin, raising the possibility that administration of branched-chain amino acids may improve protein synthesis in insulin-resistant states.

In vitro ruminal undegradable proteins of alfalfa cultivars

2000 ◽  
Vol 80 (2) ◽  
pp. 315-325 ◽  
Author(s):  
G. F. Tremblay ◽  
R. Michaud ◽  
G. Bélanger ◽  
K. B. McRae ◽  
H. V. Petit
Keyword(s):  
Protein Degradation ◽  
Dry Matter ◽  
Degradation Rate ◽  
Weight Ratio ◽  
Principal Component ◽  
Neutral Detergent Fiber ◽  
Cultivar Differences ◽  
Dry Matter Digestibility ◽  
Protein Degradation Rate

The quality of alfalfa would be greatly improved by an increase in its ruminal undegradable protein (RUP) concentration. Protein degradation rate (PDR), in vitro dry matter digestibility (IVDMD), leaf weight ratio (LWR), dry matter yield (DMY), total nitrogen (TN), in vitro RUP (expressed on both TN, RUP-TN, and dry matter basis, RUP-DM), acid detergent fiber (ADF), and neutral detergent fiber (NDF) concentrations were determined in 27 alfalfa cultivars. Cultivars were seeded in triplicate on 2 consecutive years and evaluated during the 2 subsequent production years with two harvests per year. Protein degradation rate and RUP-TN were determined using a ruminal inhibitor in vitro system. Data were averaged for spring growth, summer regrowth, and both harvests across 2 production years. Each of the three data sets was analyzed by ANOVA followed by a principal component analysis (PCA) on the ANOVA means. For the four-harvest data, cultivar differences were highly significant (P < 0.001) for all variates except for PDR (P = 0.07) and RUP-TN concentration (P = 0.10). The first PCA axis was largely defined positively by RUP-DM, IVDMD, TN, LWR, and RUP-TN, but negatively with ADF, NDF, PDR, and DMY. The second PCA axis defined a contrast between PDR versus RUP-TN, DMY, ADF, and NDF. Five cultivars were distinctive with high or low PCA scores in all three PCA. Rangelander and Heinrichs, along with Ultra, had low PDR; the first two cultivars had low DMY whereas Ultra was a medium-yielding cultivar. In contrast, Algonquin and Oneida VR had high PDR and medium DMY. While the first principal component (PC) indicated a general trend that low PDR and high RUP were associated with low-yielding cultivars, the second PC identified specific cultivars with both low PDR and high DMY. Therefore, selection for low PDR and high DMY is feasible. Key words: ruminal protein escape, dry matter digestibility, alfalfa

Transmembrane transport and intracellular kinetics of amino acids in human skeletal muscle

1995 ◽  
Vol 268 (1) ◽  
pp. E75-E84 ◽  
Author(s):  
G. Biolo ◽  
R. Y. Fleming ◽  
S. P. Maggi ◽  
R. R. Wolfe
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Human Skeletal Muscle ◽  
De Novo ◽  
Transmembrane Transport ◽  
Acid Transport ◽  
De Novo Synthesis ◽  
Intracellular Amino Acid

We have used stable isotopic tracers of amino acids to measure in vivo transmembrane transport of phenylalanine, leucine, lysine, alanine, and glutamine as well as the rates of intracellular amino acid appearance from proteolysis, de novo synthesis, and disappearance to protein synthesis in human skeletal muscle. Calculations were based on data obtained by the arteriovenous catheterization of the femoral vessels and muscle biopsy. We found that the fractional contribution of transport from the bloodstream to the total intracellular amino acid appearance depends on the individual amino acid, varying between 0.63 +/- 0.02 for phenylalanine and 0.22 +/- 0.02 for alanine. Rates of alanine and glutamine de novo synthesis were approximately eight and five times their rate of appearance from protein breakdown, respectively. The model-derived rate of protein synthesis was highly correlated with the same value calculated by means of the tracer incorporation technique. Furthermore, amino acid transport rates were in the range expected from literature values. Consequently, we conclude that our new model provides a valid means of quantifying the important aspects of protein synthesis, breakdown, and amino acid transport in human subjects.

scholarly journals Amino acids are necessary for the insulin-induced activation of mTOR/S6K1 signaling and protein synthesis in healthy and insulin resistant human skeletal muscle

2008 ◽  
Vol 27 (3) ◽  
pp. 447-456 ◽  
Author(s):  
Micah J. Drummond ◽  
Jill A. Bell ◽  
Satoshi Fujita ◽  
Hans C. Dreyer ◽  
Erin L. Glynn ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Human Skeletal Muscle ◽  
Insulin Resistant

Osteoprogenitor cells of mature human skeletal muscle tissue: an in vitro study

Bone ◽  
2001 ◽  
Vol 29 (4) ◽  
pp. 317-322 ◽  
Author(s):  
M.M Levy ◽  
C.J Joyner ◽  
A.S Virdi ◽  
A Reed ◽  
J.T Triffitt ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscle Tissue ◽  
Human Skeletal Muscle ◽  
In Vitro Study ◽  
Skeletal Muscle Tissue ◽  
Vitro Study ◽  
Osteoprogenitor Cells
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