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HIGH AFFINITY AMINO ACID TRANSPORT BY FROG SPINAL CORD SLICES
Author(s) -
Davidoff R. A.,
Adair R.
Publication year - 1975
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1975.tb07673.x
Subject(s) - aspartic acid , glycine , amino acid , glutamic acid , ouabain , biochemistry , chemistry , biophysics , stereochemistry , biology , sodium , organic chemistry
— The characteristics of amino acid uptake by frog spinal cord slices was studied by in vitro incubations in appropriate media. The uptake mechanisms exhibited saturation; kinetic analysis demonstrated 2 distinct systems for the influx of the possible neurotransmitters: GABA, glycine, L‐glutamic acid and L‐aspartic acid. One system showed a comparatively high substrate affinity (K m values, 10‐26 μM ) while the other system had a lower affinity (K m , 0.4‐1.6 mM).‐Leucine, an amino acid presumably not a transmitter, was accumulated only by a low affinity mechanism (K m 1.6 mM). The process responsible for high affinity uptake had many of the properties of an active transport mechanism. These included temperature sensitivity, energy dependence, requirement for Na + ions and inhibition by ouabain. GABA and glycine uptake was inhibited only by closely related amino acids or structural analogues. The influx of L‐glutamic acid was competitively inhibited by the presence of L‐aspartic acid in the medium; the converse was also demonstrated. Thus, the high affinity uptake system for possible transmitter amino acids in the frog spinal cord closely resembles that described for mammalian CNS tissue. These results are compatible with the assumption that GABA, glycine, L‐glutamic acid and L‐aspartic acid are neurotransmitters in the amphibian spinal cord.