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Functional heterogeneity of intracellular leucine pools in human skeletal muscle
Örebro University, School of Medical Sciences. Department of Medicine, University of Vermont, Burlington VT, United States; Department of Surgery, Karolinska Institute, Karolinska Hospital, Stockholm, Sweden.ORCID iD: 0000-0003-2636-4745
Endocrine Research Unit, Div. of Endocrinology and Metabolism, Mayo Clinic and Mayo Foundation, Rochester MN, United States.
Endocrine Research Unit, Div. of Endocrinology and Metabolism, Mayo Clinic and Mayo Foundation, Rochester MN, United States.
Endocrine Research Unit, Div. of Endocrinology and Metabolism, Mayo Clinic and Mayo Foundation, Rochester MN, United States; Mayo Clinic, Rochester MN, United States.
1997 (English)In: American Journal of Physiology, ISSN 0002-9513, E-ISSN 2163-5773, Vol. 273, no 3, p. E564-E570Article in journal (Refereed) Published
Abstract [en]

Current models to measure muscle protein synthesis in humans assume a homogeneous intracellular amino acid pool. This assumption was tested by measuring the isotopic enrichment of leucine and its transamination product alpha-ketoisocaproate (KIC) in plasma and muscle tissue fluid and comparing them with that of leucyl-tRNA during a continuous infusion of L-[1-13C]leucine in 12 healthy subjects. Six subjects were studied twice while drinking a carbohydrate (0.42 kcal/kg) drink every 20 min for 11 h or the same volume of water. Six others took an isocaloric mixed meal providing 14 mg protein/kg every 20 min and water. Enrichment of plasma and tissue fluid KIC and plasma leucine was consistently higher than that of leucyl-tRNA and tissue fluid leucine (P < 0.01), whereas the enrichment of leucyl-tRNA was equivalent to that of tissue fluid leucine in all experiments. Furthermore, the ratio of enrichment of leucyl-tRNA to that of plasma leucine and KIC decreased after the mixed meal, whereas that of leucyl-tRNA to tissue fluid leucine remained constant. The enrichment of KIC was closer (approximately 17% lower) to that of plasma leucine than that of leucyl-tRNA (approximately 43% higher), indicating that the transamination pool derived more leucine from extracellular sources than the acylation pool. We conclude that the use of plasma KIC enrichment as a surrogate measure of leucyl-tRNA enrichment substantially underestimates muscle protein synthetic rates in humans, whereas tissue fluid leucine enrichment is a valid surrogate measure. In addition, the differences in enrichment of leucyl-tRNA and KIC support a regulated cytoplasmic trafficking of leucine in muscle cells.

Place, publisher, year, edition, pages
American Physiological Society , 1997. Vol. 273, no 3, p. E564-E570
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Physiology
Identifiers
URN: urn:nbn:se:oru:diva-63875DOI: 10.1152/ajpendo.1997.273.3.E564PubMedID: 9316447Scopus ID: 2-s2.0-33745385220OAI: oai:DiVA.org:oru-63875DiVA, id: diva2:1171029
Available from: 2018-01-05 Created: 2018-01-05 Last updated: 2018-02-05Bibliographically approved

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Ljungqvist, Olle

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