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RELATIONSHIP BETWEEN SYNAPTOSOMAL UPTAKE AND RELEASE OF [ 14 C]GABA, [ 14 C]DIAMINOBUTYRIC ACID AND [ 14 C]β‐ALANINE 1
Author(s) -
Redburn Dianna A.
Publication year - 1978
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.1471-4159.1978.tb00131.x
Subject(s) - veratridine , synaptosome , chemistry , divalent , stimulation , depolarization , biophysics , potassium , alanine , biochemistry , sodium , amino acid , membrane , endocrinology , biology , organic chemistry , sodium channel
[ 14 C]GABA is taken up by rat brain synaptosomes via a high affinity, Na + ‐dependent process. Subsequent addition of depolarizing levels of potassium (56.2 MM) or veratridine (100 μM) stimulates the release of synaptosomal [ 14 C]GABA by a process which is sensitive to the external concentration of divalent cations such as Ca 2+ , Mg 2+ , and Mn 2+ . However, the relatively smaller amount of [ 14 C]GABA taken up by synaptosomes in the absence of Na + is not released from synaptosomes by Ca 2+ ‐dependent, K + ‐stimulation. [ 14 C]DABA, a competitive inhibitor of synaptosomal uptake of GABA (I versen & J ohnson , 1971) is also taken up by synaptosomal fractions via a Na + ‐dependent process; and is subsequently released by Ca 2+ ‐dependent, K + ‐stimulation. On the other hand, [ 14 C]β‐alanine, a purported blocker of glial uptake systems for GABA (S chon & K elly , 1974) is a poor competitor of GABA uptake into synaptosomes. Comparatively small amounts of [ 14 C] β‐alanine are taken up by synaptosomes and no significant amount is released by Ca 2+ ‐dependent, K + ‐stimulation. These data suggest that entry of [ 14 C]GABA into a releasable pool requires external Na + ions and maximal evoked release of [ 14 C]GABA from the synaptosomal pool requires external Ca 2+ ions. The GABA analogue, DABA, is apparently successful in entering the same or similar synaptosomal pool. The GABA analogue, β‐alanine, is not. None of the compounds or conditions studied were found to simultaneously affect both uptake and release processes. Compounds which stimulated release (veratridine) or inhibited release (magnesium) were found to have minimal effect on synaptosomal uptake. Likewise compounds (DABA) or conditions (Na + ‐free medium) which inhibited uptake, had little effect on release.