Effects of the Phosphatase Inhibitors Calyculin A and Okadaic Acid on Acetylcholine Synthesis and Content of Rat Hippocampal Formation
Version of Record online: 23 NOV 2002
Journal of Neurochemistry
Volume 66, Issue 5, pages 1924–1932, May 1996
How to Cite
Issa, A. M., Gauthier, S. and Collier, B. (1996), Effects of the Phosphatase Inhibitors Calyculin A and Okadaic Acid on Acetylcholine Synthesis and Content of Rat Hippocampal Formation. Journal of Neurochemistry, 66: 1924–1932. doi: 10.1046/j.1471-4159.1996.66051924.x
- Issue online: 23 NOV 2002
- Version of Record online: 23 NOV 2002
- Received September 19, 1995; revised manuscript received November 27, 1995; accepted December 11, 1995.
- Okadaic acid;
- Calyculin A;
- Phosphatase inhibitor;
- Serine/threonine phosphatases;
- Choline transport;
- Acetylcholine synthesis
Abstract: 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 nM) and okadaic acid (50 nM) reduced significantly (p < 0.01) the synthesis of [3H]ACh from [3H]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 [3H]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 Vmax values for high- and low-affinity choline uptake (p < 0.01) with no significant change in Km 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.