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Effects of the Phosphatase Inhibitors Calyculin A and Okadaic Acid on Acetylcholine Synthesis and Content of Rat Hippocampal Formation
Author(s) -
Issa Amalia M.,
Gauthier Serge,
Collier Brian
Publication year - 1996
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 - 10.1046/j.1471-4159.1996.66051924.x
Subject(s) - okadaic acid , phosphatase , choline , acetylcholine , choline acetyltransferase , cholinergic , chemistry , biochemistry , hippocampal formation , biology , threonine , phosphorylation , serine , medicine , endocrinology
The biochemical mechanisms involved in the regulation of acetylcholine (ACh) turnover are poorly understood. In the experiments reported here, we examined whether inhibition of the serine/threonine phosphatases 1 and 2A by calyculin A or okadaic acid alters ACh synthesis by rat hippocampal preparations. With hippocampal slices, calyculin A (50 n M ) and okadaic acid (50 n M ) reduced significantly ( p < 0.01) the synthesis of [ 3 H]ACh from [ 3 H]choline. Both calyculin A and okadaic acid produced significant depletion of endogenous tissue ACh in a concentration‐dependent manner ( p < 0.01). This depletion was not the result of a drug‐induced increase of spontaneous ACh release, which was not changed significantly ( p > 0.7) by either drug. Choline acetyltransferase (ChAT) activity from tissue exposed to calyculin A or okadaic acid was reduced in a concentration‐dependent manner ( p < 0.05), but these phosphatase inhibitors did not act directly on ChAT in vitro; i.e., enzymatic activity was not altered significantly ( p > 0.4) in the presence of calyculin A or okadaic acid. Both high‐affinity and low‐affinity [ 3 H]choline uptake by hippocampal synaptosomes were reduced significantly in a concentration‐dependent manner in the presence of calyculin A or okadaic acid; these agents reduced V max values for high‐ and low‐affinity choline uptake ( p < 0.01) with no significant change in K m values ( p > 0.1), indicating a noncompetitive inhibition. Taken together, these data suggest that phosphatase activity plays a role in presynaptic central cholinergic nerve terminal function, in particular in the modulation of ACh synthesis.