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Differential Labeling of Depot and Active Acetylcholine Pools in Nondepolarized and Potassium‐Depolarized Rat Brain Synaptosomes
Author(s) -
Suszkiw J. B.,
O'Leary M. E.
Publication year - 1982
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.1471-4159.1982.tb06648.x
Subject(s) - acetylcholine , depolarization , choline , vesicle , synaptic vesicle , cytoplasm , chemistry , biophysics , potassium , synaptosome , biochemistry , endocrinology , biology , membrane , organic chemistry
To test the hypothesis that a pool of newly synthesized acetylcholine (ACh) turns over independently of preformed ACh, compartmentation and K + ‐evoked release of ACh were examined in perfused synaptosomal beds intermittently stimulated by 50 m M K + . In resting synaptosomes, endogenous and labeled ACh was distributed between synaptic vesicles and the cytoplasm in a dynamic equilibrium ratio of 4:6. In the absence of new ACh synthesis, five sequential K + ‐depolarizations caused a decremental release of preformed labeled ACh totaling 30% of the initial transmitter store. Further depolarization evoked little additional release, despite the fact that 60% of the labeled ACh remained in these preparations. Release of the preformed [ 14 C]ACh was unaltered while new ACh was being synthesized from exogenous [ 3 H]choline. Since the evoked release of [ 3 H]ACh was maintained while that of [ 14 C]ACh was decreasing, the [ 3 H]ACh/[ 14 C]ACh ratio in perfusate increased with each successive depolarization. This ratio was six to ten times higher than the corresponding ratio in vesicles or cytoplasm. These results indicate that the newly synthesized ACh did not equilibrate with either the depot vesicular or cytoplasmic ACh pools prior to release.