Amino acid exchange between plasma and erythrocytes in vivo in humans.
To study amino acid exchange between plasma and erythrocytes in vivo, 4-h primed, continuous intravenous infusions of L-[1-13C]leucine, [15N]glycine, and L-[15N]alanine were administered to five healthy young men in the postabsorptive state. Stable isotope enrichments and amino acid levels were determined by gas chromatography-mass spectrometry in both plasma and whole blood and estimated (using hematocrit) in erythrocytes. A high concentration gradient across the erythrocyte membrane was consistently found for glycine (552 +/- 268 microM in erythrocytes vs. 155 +/- 35 microM in plasma), but not for leucine or alanine. A steady-state isotopic enrichment was observed in whole blood as well as plasma for each amino acid in every subject. Steady-state [13C]leucine enrichment in erythrocytes did not differ from plasma enrichment at steady state, the ratio of erythrocyte to plasma enrichment being 1.03 +/- 0.20 (95% confidence limits = 0.78-1.28); in contrast, this ratio reached only 0.23 +/- 0.04 and 0.59 +/- 0.09 (confidence limits 0.18-0.28 and 0.48-0.70) for [15N]glycine and [15N]alanine at steady state, respectively. These results suggest that most of erythrocyte leucine is exchangeable with plasma, whereas only a fraction of erythrocyte glycine and alanine is involved in exchange with plasma in vivo.
Darmaun
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Institut National de la Santé et de la Recherche Médicale U-290, Hopital St. Lazare, Paris, France.
Froguel
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Rongier
M
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Robert
J J
JJ
D000328:Adult; D000409:Alanine / Q000097:blood / Q000378:metabolism; D000596:Amino Acids / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D002247:Carbon Isotopes; D004912:Erythrocytes / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D005998:Glycine / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism; D006801:Humans; D007262:Infusions, Intravenous; D007930:Leucine / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism; D008297:Male; D009587:Nitrogen Isotopes
D000596:Amino Acids; D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D007930:Leucine; D000409:Alanine; D005998:Glycine