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Ammonia‐Induced Release of Neurotransmitters from Rat Brain Synaptosomes: Differences Between the Effects on Amines and Amino Acids
Author(s) -
Erecinska Maria,
Pastuszko Anna,
Wilson David F.,
Nelson David
Publication year - 1987
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.1471-4159.1987.tb10018.x
Subject(s) - chemistry , depolarization , dopamine , amino acid , biophysics , glutamate receptor , biogenic amine , stimulation , neurotransmitter , membrane potential , biochemistry , endocrinology , biology , receptor
The effect of NH 4 Cl on release of amine and amino acid transmitters from rat brain synaptosomes was investigated. Ammonia (0.1–10 m M ) stimulated the secretion of dopamine and 5‐hydroxytryptamine in a dose‐dependent manner, in a process which was additive with the effect of 40 m M K + , almost unaffected by withdrawal of Ca 2+ , and markedly decreased by increasing [H + ] in the medium. The NH 4 Cl‐induced dopamine efflux, in contrast to that caused by high [K + ] e , was inhibited by benztropine. The release of γ‐aminobutyric acid, aspartate, and glutamate was unaltered by [NH 4 Cl] < 5 m M , but somewhat stimulated at higher levels. Transmembrane pH gradient, acid inside, was dissipated by NH 4 Cl in a concentration‐dependent manner and the internal alkalinization correlated with the stimulation of the rate of dopamine efflux. Transmembrane electrical potential was unaffected by [ammonia] < 5 m M , but a small depolarization was observed at higher levels. It is postulated that ammonia‐induced alkalinization of the intrasynaptic storage granules causes extrusion of amines into the cytoplasm and their subsequent leakage into the medium through a reversal of the plasma membrane transporters. A lack of correlation between the release of amino acid neurotransmitters and the dissipation of the ΔpH suggests that in rat brain intrasynaptic vesicles, acidic inside, are unlikely to store substantial amounts of γ‐aminobutyric acid, aspartate, or glutamate.