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IN VITRO EXPERIMENTS ON THE METABOLISM, ACCUMULATION AND RELEASE OF 5‐HT IN THE NERVOUS SYSTEM OF THE SNAIL HELIX POMATIA
Author(s) -
Osborne N. N.,
Neuhoff V.
Publication year - 1974
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.1471-4159.1974.tb07601.x
Subject(s) - incubation , helix pomatia , tryptophan , ouabain , metabolism , serotonin , dinitrophenol , 5 ht receptor , biochemistry , chemistry , in vitro , endocrinology , medicine , biology , snail , sodium , amino acid , receptor , ecology , organic chemistry
— The accumulation, metabolism and stimulated‐induced release of 5‐HT in the nervous system of the snail was studied. When nervous tissue was incubated at 24°C in a medium containing [ 14 C]5‐HT or [ 3 H]tryptophan, tissue: medium ratios of about 25:1 and 4:1 respectively were obtained after 45 min incubation. The process responsible for [ 14 C]5‐HT accumulation showed properties of an active transport system: it was temperature sensitive and was greatly inhibited by dinitrophenol and ouabain. Furthermore, the accumulation process was inhibited by imipramine and desipramine. Of a number of analogues of indole, N ‐acetyl‐5‐HT and 5‐hydroxytryptophan were the most potent in the inhibition of the accumulation of [ 14 C]5‐HT. The presence of a large molar excess of amino acids had little effect. A small amount (less than 14 per cent) of the accumulated [ 14 C]5‐HT was metabolized to form 5‐hydroxyindole acetic acid, even after long periods (2 h) of incubation. The accumulated [ 3 H]tryptophan was metabolized to form 5‐hydroxytryptophan and 5‐HT; the content of formed [ 3 H]5‐HT increased with incubation time whilst the [ 3 H]5‐hydroxytryptophan remained more or less constant. The presence of p ‐chlorophenylalanine in the incubation medium did not interfere with the accumulation of [ 3 H]tryptophan, though it inhibited the formation of [ 3 H]5‐hydroxytryptophan and to a greater extent [ 3 H]5‐HT. A rapid efflux of the accumulated [ 14 C]5‐HT from snail nervous tissue was observed on electrical stimulation. Slower release resulted when the Ca 2+ ion content of the incubation medium was replaced by Mg 2+ ions. There is also a slight efflux of radioactive substances following electrical stimulation in tissues previously incubated in [ 3 H]tryptophan. Most of this radioactivity was attributed to the formed [ 3 H]5‐HT. The data support the idea that 5‐HT is a transmitter‐substance in the snail Helix pomatia , and that re‐uptake of the substance is a method of inactivating the released amine.