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The Effect of Ouabain on the Release of [ 14 C]Acetylcholine and Other Substances from Synaptosomes
Author(s) -
Vyas S.,
Marchbanks R. M.
Publication year - 1981
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.1471-4159.1981.tb06316.x
Subject(s) - ouabain , chemistry , acetylcholine , depolarization , choline , synaptosome , calcium , choline chloride , efflux , biophysics , sodium , endocrinology , medicine , biochemistry , membrane , biology , organic chemistry
The effect of ouabain and dihydroouabain on Na + ‐K + ATPase, 86 Rb uptake and the release of [ 14 C]ACh (acetylcholine) from synaptosomal preparations of guinea pigs was compared. At low concentrations of glycoside (<50 μ m ) there was a good correlation between the potency of ouabain and of dihydroouabain in inhibiting Na + ‐K + ATPase and in causing the release of [ l4 C]ACh in a nondepolarising medium. Ouabain (200 μM) increased the release of [ 14 C]ACh evoked by 25 m m ‐KCl, but not that evoked by 100 μ m ‐veratrine. The enhancement of release was independent of the presence of calcium. It was observed that in addition to [ 14 C]ACh release, choline efflux was also stimulated by ouabain, independently of the presence of Ca 2+ . Experiments with hemicholinium‐3 showed that the ouabain‐induced increase in choline efflux was not due to an inhibition of reuptake. The effect of ouabain on intrasynaptosomal K + concentration was measured in order to investigate the degree of depolarisation it caused. The decrease in K + was found to be similar in magnitude and time course to that caused by veratrine. It was shown that ouabain‐induced depolarisation caused an increased efflux of another positive ion (dibenzyldimethylammonium chloride) and retention of a negatively charged ion (chloride), as would be expected from the operation of the electrochemical potential gradient changing as a result of depolarisation. It is suggested that ouabain acts to stimulate ACh release from synaptosomes as follows: following blockage of the Na + ‐K + ATPase there is rapid depolarisation which, if Ca 2+ is present, provokes the normal Ca 2+ ‐dependent transmitter release process to occur. In addition, depolarisation accelerates the leakage of positive ions down their electrochemical potential gradient, but causes a retention of negative ions. Such an action does not depend on the presence of Ca 2+ , nor is it specific to transmitters.