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ACCELERATION OF CHOLINE UPTAKE AFTER DEPOLARIZATION‐INDUCED ACETYLCHOLINE RELEASE IN RAT CORTICAL SYNAPTOSOMES
Author(s) -
Roskoski Robert
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.tb10466.x
Subject(s) - choline , acetylcholine , divalent , chemistry , synaptosome , calcium , depolarization , biophysics , incubation , mole , in vivo , neurotransmitter , cholinergic , biochemistry , in vitro , chromatography , endocrinology , biology , receptor , organic chemistry , microbiology and biotechnology
— Activation of nerve elements in vivo and in vitro is associated with an increased rate of choline uptake by a Na + ‐dependent high affinity transport system. Following the methodology of B arker (1976), rat cortical synaptosomes were depolarized (37°C, 10min) by 25mM‐KCl in the presence of CaCl 2 (1 mM) or other divalent cations. After reisolation by centrifugation, the rate of 3 H‐choline uptake (1.25μM) was measured by Millipore filtration. KCl treatment alone failed to accelerate the rate of uptake in the reisolated synaptosomes. CaCl 2 , BaC1 2 or SrCl 2 (but not MgCl 2 or MnCl 2 ) were necessary (1 mM) to observe the KCl induced acceleration. Moreover, RbCl, but not LiCl or CsCl, also produced the calcium‐dependent rate enhancement in the reisolated synaptosomes. The conditions mediating the enhanced rate of choline uptake correlated strongly with those associated with neurotransmitter release. To test this possibility, synaptosomal acetylcholine content was measured in response to the various salt treatments. Treatment with KCI (25 mM) and CaCl 2 (1 mM), but not KCl alone, reduced the synaptosomal acetylcholine content from 154 to 113pmol/mg protein. The respective rates of choline uptake increased about 60%. The increased rate was reversed by incubation with 50 μM‐choline followed by synaptosome reisolation. This procedure also normalized the acetylcholine content. In summary, the rate of choline uptake by the high affinity choline uptake system is inversely related to the synaptosomal acetylcholine content.