期刊
AMERICAN JOURNAL OF PHYSIOLOGY-ENDOCRINOLOGY AND METABOLISM
卷 295, 期 3, 页码 E595-E604出版社
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpendo.90411.2008
关键词
muscle protein synthesis; muscle protein breakdown
资金
- Iovate, Mississauga, ON, Canada
- United Kingdom (UK) Medical Research Council [G 99000163]
- UK Biotechnology and Biological Sciences Research Council [BB/X510697/1, BB/C516779/1]
- Wellcome Trust [056885/Z/99]
- European Community
- MRC [G0401644] Funding Source: UKRI
- Biotechnology and Biological Sciences Research Council [BB/C516779/1] Funding Source: researchfish
- Medical Research Council [G0401644] Funding Source: researchfish
We determined the effects of intravenous infusion of amino acids (AA) at serum insulin of 5, 30, 72, and 167 mU/l on anabolic signaling, expression of ubiquitin-proteasome components, and protein turnover in muscles of healthy young men. Tripling AA availability at 5 mU/l insulin doubled incorporation of [1-C-13] leucine [i.e., muscle protein synthesis ( MPS), P < 0.01] without affecting the rate of leg protein breakdown (LPB; appearance of d(5)-phenylalanine). While keeping AA availability constant, increasing insulin to 30 mU/l halved LPB (P < 0.05) without further inhibition at higher doses, whereas rates of MPS were identical to that at 5 mU/l insulin. The phosphorylation of PKB Ser(473) and (p)70(S6k) Thr(389) increased concomitantly with insulin, but whereas raising insulin to 30 mU/l increased the phosphorylation of mTOR Ser(2448), 4E-BP1 Thr(37/46), or GSK3 beta Ser(9) and decreased that of eEF2 Thr(56), higher insulin doses to 72 and 167 mU/l did not augment these latter responses. MAFbx and proteasome C2 subunit proteins declined as insulin increased, with MuRF-1 expression largely unchanged. Thus increasing AA and insulin availability causes changes in anabolic signaling and amounts of enzymes of the ubiquitin-proteasome pathway, which cannot be easily reconciled with observed effects on MPS or LPB.
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