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Mechanisms by which human blood platelets accumulate glycine, gaba and amino acid precursors of putative neurotransmitters
Author(s) -
BOULLIN D. J.,
GREEN A. R.
Publication year - 1972
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1972.tb09579.x
Subject(s) - phenylalanine , amino acid , tyrosine , glycine , tryptophan , platelet , incubation , biochemistry , metabolism , chemistry , intracellular , biology , immunology
Summary1 . We have examined the accumulation by human blood platelets of amino acids that are believed to be involved in neurohumoral transmission in the central nervous system. 2 . Platelets were incubated in Ca ++ ‐free Krebs solution at 37° C with radioactive amino acids for various times and then the platelets were analysed for the radioactive substance and its metabolites. 3 . l ‐Phenylalanine, l ‐DOPA, l ‐tryptophan and l ‐tyrosine were rapidly accumulated, the equilibrium tissue/medium concentration ratio ( C i / C o ) being greater than 10: 1 when the concentration of amino acid in the medium was 10 −7 m or lower. Glycine and γ‐aminobutyric acid (GABA) accumulation was less, C i / C o being lower than 3: 1 when C o was 10 −7 m . 4 . Uptake of l ‐phenylalanine, l ‐DOPA and l ‐tryptophan were all decreased or abolished by incubation at 4° C, or with metabolic inhibitors or by disruption of the platelet membrane prior to incubation, while l ‐tyrosine accumulation was not affected. 5 . It is considered that l ‐phenylalanine, l ‐DOPA and l ‐tryptophan are accumulated by saturable, energy‐dependent processes; that glycine and GABA diffuse into the platelet, and l ‐tyrosine accumulates as a result of diffusion and intracellular binding. 6 . None of the amino acids examined showed any significant metabolism during a 20 min incubation. However, some evidence for tyrosine binding to soluble protein was obtained. 7 . Results are compared to reports of accumulation of these amino acids by the central nervous system.