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Zhou Q, Zheng Z, Wang X, Li W, Wang L, Yin C, Zhang Q, Wang Q. taVNS Alleviates Sevoflurane-Induced Cognitive Dysfunction in Aged Rats Via Activating Basal Forebrain Cholinergic Neurons. Neurochem Res 2023; 48:1848-1863. [PMID: 36729311 DOI: 10.1007/s11064-023-03871-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 12/24/2022] [Accepted: 01/21/2023] [Indexed: 02/03/2023]
Abstract
Postoperative cognitive dysfunction (POCD) is a common complication of central nervous system after anesthesia or surgery. Sevoflurane, an inhalation anesthetic, may inhibit cholinergic pathway that induce neuronal death and neuroinflammation, ultimately leading to POCD. Transauricular vagus nerve stimulation (taVNS) has neuroprotective effects in POCD rats, but the mechanisms related to cholinergic system have not been revealed. Sprague-Dawley rats were anesthetized with sevoflurane to construct the POCD model. The immunotoxin 192-IgG-saporin (192-sap) selectively lesioned cholinergic neurons in the basal forebrain, which is the major source of cholinergic projections to hippocampus. After lesion, rats received 5 days of taVNS treatment (30 min per day) starting 24 h before anesthesia. Open field test and Morris water maze were used to test the cognitive function. In this study, rats exposed to sevoflurane exhibited cognitive impairment that was attenuated by taVNS. In addition, taVNS treatment activated cholinergic system in the basal forebrain and hippocampus, and downregulated the expression of apoptosis- and necroptosis-related proteins, such as cleaved Caspase-3 and p-MLKL, in the hippocampus. Meanwhile, the activation of Iba1+ microglial by sevoflurane was reduced by taVNS. 192-sap blocked the cholinergic system activation in the basal forebrain and hippocampus and inhibited taVNS-mediated neuroprotection and anti-inflammation effects in the hippocampus. Generally, our study indicated that taVNS might alleviate sevoflurane-induced hippocampal neuronal apoptosis, necroptosis and microglial activation though activating cholinergic system in the basal forebrain.
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Affiliation(s)
- Qi Zhou
- Department of Anesthesiology, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei, China
| | - Zilei Zheng
- Department of Anesthesiology, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei, China.,Department of Anesthesiology, Zhangjiakou Second Hospital, Zhangjiakou, Hebei, China
| | - Xupeng Wang
- Department of Anesthesiology, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei, China
| | - Wei Li
- Department of Anesthesiology, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei, China
| | - Luqi Wang
- Department of Radiology, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei, China
| | - Chunping Yin
- Department of Anesthesiology, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei, China
| | - Qi Zhang
- Department of Anesthesiology, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei, China.,Department of Anesthesiology, Hebei Children's Hospital Affiliated to Hebei Medical University, Shijiazhuang, Hebei, China
| | - Qiujun Wang
- Department of Anesthesiology, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei, China.
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Muramatsu I, Uwada J, Chihara K, Sada K, Wang MH, Yazawa T, Taniguchi T, Ishibashi T, Masuoka T. Evaluation of radiolabeled acetylcholine synthesis and release in rat striatum. J Neurochem 2021; 160:342-355. [PMID: 34878648 DOI: 10.1111/jnc.15556] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Revised: 10/18/2021] [Accepted: 11/30/2021] [Indexed: 12/26/2022]
Abstract
Cholinergic transmission underlies higher brain functions such as cognition and movement. To elucidate the process whereby acetylcholine (ACh) release is maintained and regulated in the central nervous system, uptake of [3 H]choline and subsequent synthesis and release of [3 H]ACh were investigated in rat striatal segments. Incubation with [3 H]choline elicited efficient uptake via high-affinity choline transporter-1, resulting in accumulation of [3 H]choline and [3 H]ACh. However, following inhibition of ACh esterase (AChE), incubation with [3 H]choline led predominantly to the accumulation of [3 H]ACh. Electrical stimulation and KCl depolarization selectively released [3 H]ACh but not [3 H]choline. [3 H]ACh release gradually declined upon repetitive stimulation, whereas the release was reproducible under inhibition of AChE. [3 H]ACh release was abolished after treatment with vesamicol, an inhibitor of vesicular ACh transporter. These results suggest that releasable ACh is continually replenished from the cytosol to releasable pools of cholinergic vesicles to maintain cholinergic transmission. [3 H]ACh release evoked by electrical stimulation was abolished by tetrodotoxin, but that induced by KCl was largely resistant. ACh release was Ca2+ dependent and exhibited slightly different sensitivities to N- and P-type Ca2+ channel toxins (ω-conotoxin GVIA and ω-agatoxin IVA, respectively) between both stimuli. [3 H]ACh release was negatively regulated by M2 muscarinic and D2 dopaminergic receptors. The present results suggest that inhibition of AChE within cholinergic neurons and of presynaptic negative regulation of ACh release contributes to maintenance and facilitation of cholinergic transmission, providing a potentially useful clue for the development of therapies for cholinergic dysfunction-associated disorders, in addition to inhibition of synaptic cleft AChE.
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Affiliation(s)
- Ikunobu Muramatsu
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, Uchinada, Ishikawa, Japan.,Division of Genomic Science and Microbiology, School of Medicine, University of Fukui, Eiheiji, Fukui, Japan.,Kimura Hospital, Awara, Fukui, Japan
| | - Junsuke Uwada
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, Uchinada, Ishikawa, Japan.,Division of Cellular Signal Transduction, Department of Biochemistry, Asahikawa Medical University, Asahikawa, Hokkaido, Japan
| | - Kazuyasu Chihara
- Division of Genomic Science and Microbiology, School of Medicine, University of Fukui, Eiheiji, Fukui, Japan
| | - Kiyonao Sada
- Division of Genomic Science and Microbiology, School of Medicine, University of Fukui, Eiheiji, Fukui, Japan
| | - Mao-Hsien Wang
- Division of Genomic Science and Microbiology, School of Medicine, University of Fukui, Eiheiji, Fukui, Japan.,Department of Anesthesia, En Chu Kon Hospital, New Taipei City, Taiwan, ROC
| | - Takashi Yazawa
- Division of Cellular Signal Transduction, Department of Biochemistry, Asahikawa Medical University, Asahikawa, Hokkaido, Japan
| | - Takanobu Taniguchi
- Division of Cellular Signal Transduction, Department of Biochemistry, Asahikawa Medical University, Asahikawa, Hokkaido, Japan
| | - Takaharu Ishibashi
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, Uchinada, Ishikawa, Japan
| | - Takayoshi Masuoka
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, Uchinada, Ishikawa, Japan
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Shen H, Zheng Y, Chen R, Huang X, Shi G. Neuroprotective effects of quercetin 3-O-sophoroside from Hibiscus rosa-sinensis Linn. on scopolamine-induced amnesia in mice. J Funct Foods 2021. [DOI: 10.1016/j.jff.2020.104291] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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Mohamed Ahmed IA, Eltayeb MM, Habora ME, Eltayeb AE, Arima J, Mori N, Taniguchi T, Yamanaka N. Identification of the key genes involved in the degradation of homocholine by Pseudomonas sp. strain A9 by using suppression subtractive hybridization. Process Biochem 2017. [DOI: 10.1016/j.procbio.2016.10.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Ferreira-Vieira TH, Guimaraes IM, Silva FR, Ribeiro FM. Alzheimer's disease: Targeting the Cholinergic System. Curr Neuropharmacol 2016; 14:101-15. [PMID: 26813123 PMCID: PMC4787279 DOI: 10.2174/1570159x13666150716165726] [Citation(s) in RCA: 878] [Impact Index Per Article: 109.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2014] [Revised: 07/01/2015] [Accepted: 07/14/2015] [Indexed: 12/16/2022] Open
Abstract
Acetylcholine (ACh) has a crucial role in the peripheral and central nervous
systems. The enzyme choline acetyltransferase (ChAT) is responsible for
synthesizing ACh from acetyl-CoA and choline in the cytoplasm and the vesicular
acetylcholine transporter (VAChT) uptakes the neurotransmitter into synaptic
vesicles. Following depolarization, ACh undergoes exocytosis reaching the
synaptic cleft, where it can bind its receptors, including muscarinic and
nicotinic receptors. ACh present at the synaptic cleft is promptly hydrolyzed by
the enzyme acetylcholinesterase (AChE), forming acetate and choline, which is
recycled into the presynaptic nerve terminal by the high-affinity choline
transporter (CHT1). Cholinergic neurons located in the basal forebrain,
including the neurons that form the nucleus basalis of Meynert, are severely
lost in Alzheimer’s disease (AD). AD is the most ordinary cause of dementia
affecting 25 million people worldwide. The hallmarks of the disease are the
accumulation of neurofibrillary tangles and amyloid plaques. However, there is
no real correlation between levels of cortical plaques and AD-related cognitive
impairment. Nevertheless, synaptic loss is the principal correlate of disease
progression and loss of cholinergic neurons contributes to memory and attention
deficits. Thus, drugs that act on the cholinergic system represent a promising
option to treat AD patients.
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Affiliation(s)
| | | | | | - Fabiola M Ribeiro
- Departamento de Bioquimica e Imunologia, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
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Maeda S, Jun JG, Kuwahara-Otani S, Tanaka K, Hayakawa T, Seki M. Non-neuronal expression of choline acetyltransferase in the rat kidney. Life Sci 2011; 89:408-14. [PMID: 21798270 DOI: 10.1016/j.lfs.2011.07.011] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2011] [Revised: 06/27/2011] [Accepted: 07/09/2011] [Indexed: 01/11/2023]
Abstract
AIMS Acetylcholine (ACh) has been shown to increase ion and water excretion in the kidneys, resulting in hypotension. However, no evidence of renal parasympathetic innervation has been shown, and the source of ACh acting on nephrons is still unknown. The aim of the present study was to identify ACh-producing cells in the rat kidney, by examining the expression of cholinergic agents and localization of an ACh-synthesizing enzyme, choline acetyltransferase (ChAT), in the kidney. MAIN METHODS Adult mail Sprague-Dawley rats were used in this study. Expression of mRNA of cholinergic agents, ChAT, vesicular ACh transporter (VAChT), and high-affinity choline transporter (CHT-1), in the kidney was examined by RT-PCR. Localization of ChAT mRNA and protein was examined by in situ hybridization and tyramide-enhanced immunohistochemistry, respectively. KEY FINDINGS RT-PCR showed the expression of ChAT, VAChT, and CHT-1. In situ hybridization demonstrated that ChAT mRNA is localized to the renal cortical collecting ducts (CCD). Immunohistochemistry showed that the ChAT-positive cells were principal cells, and that they were unevenly distributed in the tubules, and constituted approximately 15.2% of CCD in the cortex, and 3.6% and 1.5% in the outer and inner medulla, respectively. ChAT-positive immunoreactivity was localized to the apical side of principal cells, suggesting that ACh synthesis may occur in the apical compartment of these cells. SIGNIFICANCE These results suggest that the cholinergic effects in the nephron may be mediated at least in part by ACh originating from CCD principal cells and its expression may be locally regulated in the rat kidney.
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Affiliation(s)
- Seishi Maeda
- Department of Anatomy and Cell Biology, Hyogo College of Medicine, 1-1 Mukogawa, Nishinomiya, Hyogo 663-8501, Japan.
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Bellier JP, Kimura H. Peripheral type of choline acetyltransferase: biological and evolutionary implications for novel mechanisms in cholinergic system. J Chem Neuroanat 2011; 42:225-35. [PMID: 21382474 DOI: 10.1016/j.jchemneu.2011.02.005] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2010] [Revised: 02/23/2011] [Accepted: 02/24/2011] [Indexed: 01/29/2023]
Abstract
The peripheral type of choline acetyltransferase (pChAT) is an isoform of the well-studied common type of choline acetyltransferase (cChAT), the synthesizing enzyme of acetylcholine. Since pChAT arises by exons skipping, its amino acid sequence is similar to that of cChAT, except the lack of a continuous peptide sequence encoded by all the four exons from 6 to 9. While cChAT expression has been observed in both the central and peripheral nervous systems, pChAT is preferentially expressed in the peripheral nervous system. pChAT appears to be a reliable marker for the visualization of peripheral cholinergic neurons and their processes, whereas other conventional markers including cChAT have not been used successfully for it. In mammals like rodents, pChAT immunoreactivity has been observed in most, if not all, physiologically identified peripheral cholinergic structures such as all parasympathetic postganglionic neurons and most neurons of the enteric nervous system. In addition, pChAT has been found in many peripheral neurons that are derived from the neural crest. These include sensory neurons of the trigeminal ganglion and the dorsal root ganglion, and sympathetic postganglionic neurons. Recent studies moreover indicate that pChAT, as well as cChAT, appears ubiquitously expressed among various species not only of vertebrate mammals but also of invertebrate mollusks. This finding implies that the alternative splicing mechanism to generate pChAT and cChAT has been preserved during evolution, probably for some functional benefits.
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Affiliation(s)
- J-P Bellier
- Molecular Neuroscience Research Center, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
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Auld DS, Mennicken F, Day JC, Quirion R. Neurotrophins differentially enhance acetylcholine release, acetylcholine content and choline acetyltransferase activity in basal forebrain neurons. J Neurochem 2008. [DOI: 10.1046/j.1471-4159.2001.00234.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Kim AR, Rylett RJ, Shilton BH. Substrate binding and catalytic mechanism of human choline acetyltransferase. Biochemistry 2007; 45:14621-31. [PMID: 17144655 DOI: 10.1021/bi061536l] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Choline acetyltransferase (ChAT) catalyzes the synthesis of the neurotransmitter acetylcholine from choline and acetyl-CoA, and its presence is a defining feature of cholinergic neurons. We report the structure of human ChAT to a resolution of 2.2 A along with structures for binary complexes of ChAT with choline, CoA, and a nonhydrolyzable acetyl-CoA analogue, S-(2-oxopropyl)-CoA. The ChAT-choline complex shows which features of choline are important for binding and explains how modifications of the choline trimethylammonium group can be tolerated by the enzyme. A detailed model of the ternary Michaelis complex fully supports the direct transfer of the acetyl group from acetyl-CoA to choline through a mechanism similar to that seen in the serine hydrolases for the formation of an acyl-enzyme intermediate. Domain movements accompany CoA binding, and a surface loop, which is disordered in the unliganded enzyme, becomes localized and binds directly to the phosphates of CoA, stabilizing the complex. Interactions between this surface loop and CoA may function to lower the KM for CoA and could be important for phosphorylation-dependent regulation of ChAT activity.
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Affiliation(s)
- Ae-Ri Kim
- Department of Biochemistry, and Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, Ontario, Canada
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10
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Heo HJ, Suh YM, Kim MJ, Choi SJ, Mun NS, Kim HK, Kim E, Kim CJ, Cho HY, Kim YJ, Shin DH. Daidzein activates choline acetyltransferase from MC-IXC cells and improves drug-induced amnesia. Biosci Biotechnol Biochem 2006; 70:107-11. [PMID: 16428827 DOI: 10.1271/bbb.70.107] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The choline acetyltransferase (ChAT) activator, which enhances cholinergic transmission via an augmentation of the enzymatic production of acetylcholine (ACh), is an important factor in the treatment of Alzheimer's disease (AD). Methanolic extracts from Pueraria thunbergiana exhibited an activation effect (46%) on ChAT in vitro. Via the sequential isolation of Pueraria thunbergiana, the active component was ultimately identified as daidzein (4',7-dihydroxy-isoflavone). In order to investigate the effects of daidzein from Pueraria thunbergiana on scopolamine-induced impairments of learning and memory, we conducted a series of in vivo tests. Administration of daidzein (4.5 mg/kg body weight) to mice was shown significantly to reverse scopolamine-induced amnesia, according to the results of a Y-maze test. Injections of scopolamine into mice resulted in impaired performance on Y-maze tests (a 37% decreases in alternation behavior). By way of contrast, mice treated with daidzein prior to the scopolamine injections were noticeably protected from this performance impairment (an approximately 12%-21% decrease in alternation behavior). These results indicate that daidzein might play a role in acetylcholine biosynthesis as a ChAT activator, and that it also ameliorates scopolamine-induced amnesia.
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Affiliation(s)
- Ho Jin Heo
- Jeonnam Innovation Agency, Jeonnam, Korea
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Abstract
Choline acetyltransferase (ChAT) synthesizes the neurotransmitter acetylcholine (ACh) and is a phenotypic marker for cholinergic neurons. Cholinergic neurons in brain are involved in cognitive function, attentional processing and motor control, and decreased ChAT activity is found in several neurological disorders including Alzheimer's disease. Dysregulation of ChAT and cholinergic communication is also associated with some spontaneous point-mutations in ChAT that alter its substrate binding kinetics, or by disruption of signaling pathways that could regulate protein kinases for which ChAT is a substrate. It has been identified recently that the catalytic activity and subcellular distribution of ChAT, and its interaction with other cellular proteins, can be modified by phosphorylation of the enzyme by protein kinase-C and Ca2+/calmodulin-dependent protein kinase II; these kinases appear also to mediate some of the effects of beta-amyloid peptides on cholinergic neuron functions, including the effects on ChAT. This review outlines a new model for the regulation of cholinergic transmission at the level of the presynaptic terminal that is mediated by hierarchically-regulated, multi-site phosphorylation of ChAT.
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Affiliation(s)
- Tomas Dobransky
- Cell Biology Group, Robarts Research Institute, and Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
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Hossain MM, Suzuki T, Sato I, Takewaki T, Suzuki K, Kobayashi H. Neuromechanical effects of pyrethroids, allethrin, cyhalothrin and deltamethrin on the cholinergic processes in rat brain. Life Sci 2005; 77:795-807. [PMID: 15936353 DOI: 10.1016/j.lfs.2005.01.014] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2004] [Accepted: 01/05/2005] [Indexed: 11/28/2022]
Abstract
Our previous microdialysis study of freely moving rats demonstrated that 3 pyrethroids, allethrin (type I), cyhalothrin (type II) and deltamethrin (type II) differentially modulate acetylcholine (ACh) release in the hippocampus. To better understand the mechanisms of their modulatory effects and also other effects on the cholinergic system in the brain, the activities of ACh hydrolyzing enzyme acetylcholinesterase (AChE), ACh synthesizing enzyme choline acetyltransferase (ChAT) and ACh synthesizing rate-limiting step, high-affinity choline uptake (HACU) were examined in the present study. The pyrethroids studied had no effect on AChE activity in the cortex, hippocampus and striatum. These pyrethroids had no significant effect on ChAT in the cortex and hippocampus, but striatal ChAT was increased at higher dosage (60 mg/kg) by all three compounds. Lineweaver-Burk analysis of hippocampal HACU revealed that the pyrethroids did not alter the Michaelis-Menten constant (Km) value but caused alteration of maximal velocity (Vmax). Allethrin (60 mg/kg) and cyhalothrin (20 and 60 mg/kg) decreased while deltamethrin (60 mg/kg) increased the Vmax for HACU. In vitro study showed that at higher concentrations (> or = 10(-) (6) M) allethrin and cyhalothrin reduced the hippocampal HACU but deltamethrin increased it. These results suggest that mechanisms of ACh synthesis are involved in the modulatory effects of the pyrethroids on ACh release and other cholinergic activities.
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Affiliation(s)
- Muhammad Mubarak Hossain
- Department of Veterinary Medicine, Faculty of Agriculture, Iwate University, Morioka 020-8550, Japan.
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Heo HJ, Park YJ, Suh YM, Choi SJ, Kim MJ, Cho HY, Chang YJ, Hong B, Kim HK, Kim E, Kim CJ, Kim BG, Shin DH. Effects of oleamide on choline acetyltransferase and cognitive activities. Biosci Biotechnol Biochem 2003; 67:1284-91. [PMID: 12843655 DOI: 10.1271/bbb.67.1284] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We screened 50 Korean traditional natural plants to measure the activation effect on choline acetyltransferase and attenuation of scopolamine-induced amnesia. The methanolic extracts from Zizyphus jujuba among the tested 50 plants, showed the highest activatory effect (34.1%) on choline acetyltransferase in vitro. By sequential fractionation of Zizyphus jujuba, the active component was finally identified as cis-9-octadecenoamide (oleamide). After isolation, oleamide showed a 65% activation effect. Administration of oleamide (0.32%) to mice significantly reversed the scopolamine-induced memory and/or cognitive impairment in the passive avoidance test and Y-maze test. Injection of scopolamine to mice impaired performance on the passive avoidance test (31% decrease in step-through latency), and on the Y-maze test (16% decrease in alternation behavior). In contrast, mice treated with oleamide before scopolamine injection were protected from these changes (12-25% decrease in step-through latency; 1-10% decrease in alternation behavior). These results suggest that oleamide should be a useful chemo-preventive agent against Alzheimer's disease.
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Affiliation(s)
- Ho-Jin Heo
- Graduate School of Biotechnology, Korea University, Seoul 136-701, Korea
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Gabrielle P, Jeana M, Lorenza EC. Cytosolic choline acetyltransferase binds specifically to cholinergic plasma membrane of rat brain synaptosomes to generate membrane-bound enzyme. Neurochem Res 2003; 28:543-9. [PMID: 12675143 DOI: 10.1023/a:1022825407631] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Uncovering the way membrane-bound choline acetyltransferase (ChAT) interacts with membranes and with which membrane in cholinergic neurons may help in understanding its role in acetylcholine metabolism. Subfractionation of rat hippocampal synaptosomes aiming to separate synaptic vesicles from plasma membranes shows that membrane-bound ChAT is bound to plasma membrane. Either detergents or urea and alkali can solubilize membrane-bound enzyme. Detergent-solubilized enzyme has a higher sedimentation rate than urea-alkali solubilized or cytosolic ChAT. Once dissociated, membrane-bound ChAT reassociates specifically with cholinergic plasma membranes, a process that was abolished by previous treatment of membranes with trypsin. Cytosolic ChAT behaves similarly. Thus, in cholinergic synaptosomes, ChAT exists as cytosolic and peripheral activity. Cytosolic ChAT generates peripheral enzyme most probably by interacting with a protein of plasma membrane of cholinergic nerve terminals. This "receptor" protein might regulate the amount of membrane-bound ChAT in cholinergic neurons.
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Affiliation(s)
- Pahud Gabrielle
- Department of Pharmacology (APSIC), Centre Médical Universitaire, 1, rue Michel Servet, 1211 Geneva 4, Switzerland
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15
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Jonnala RR, Graham JH, Terry AV, Beach JW, Young JA, Buccafusco JJ. Relative levels of cytoprotection produced by analogs of choline and the role of alpha7-nicotinic acetylcholine receptors. Synapse 2003; 47:262-9. [PMID: 12539199 DOI: 10.1002/syn.10176] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Several analogs of the acetylcholine precursor molecule choline have been widely studied as potential false cholinergic neurotransmitters with the therapeutic goal of using them to limit cholinergic neurotransmission. More recently, choline itself has been shown to act as a full, if low potency, agonist at the alpha7 subtype of the nicotinic acetylcholine receptor. This pharmacological property has been associated with the ability of nicotine and other related alpha7 receptor agonists to offer neuroprotection in a variety of experimental models. We confirm here that choline offers a significant degree of protection against the cytotoxicity induced by growth factor deprivation in differentiated PC-12 cells. Choline-induced cytoprotection ( approximately 1 mM) was about 3 orders of magnitude less potent than that for nicotine (EC(50) = 0.7 microM). Choline also exhibited only about 40% of the full cytoprotective effect of nicotine. Ethyl substitution for choline's N-methyl groups did not result in a significant improvement over choline as a cytoprotective agent. In contrast, pyrrolidinecholine exhibited much greater potency (EC(50) = 20 microM) and increased efficacy (about 55% of nicotine's effect) than choline. Like choline and nicotine, pyrrolidinecholine fully displaced [(125)I]alpha-bungarotoxin binding (K(i) = 33 microM) and chronic exposure to the analog increased cell surface binding sites. The cytoprotective effects of the analog were completely inhibited by coincubation with methyllycaconitine (MLA), a selective alpha7-nicotinic receptor antagonist. These findings are consistent with the possibility that the choline structure may serve as a template for the development of novel agents with both alpha7-nicotinic agonist activity and potential neuroprotective ability, as many of these compounds, including pyrrolidinecholine, are transported along with choline into the central nervous system.
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Affiliation(s)
- Ramamohana R Jonnala
- Alzheimer's Research Center, Medical College of Georgia, Augusta, Georgia 30912-2300l, USA
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Zambrzycka A, Alberghina M, Strosznajder JB. Effects of aging and amyloid-beta peptides on choline acetyltransferase activity in rat brain. Neurochem Res 2002; 27:277-81. [PMID: 11958528 DOI: 10.1023/a:1014951010834] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Choline acetyltransferase (ChAT, acetyl-CoA:choline O-acetyltransferase, EC 2.3.1.6), involved in the learning and memory processes is responsible for the synthesis of acetylcholine. There are many discrepancies in literature concerning ChAT activity during brain aging and the role of amyloid beta peptides in modulation of this enzyme. The aim of the study was to investigate the mechanism of ChAT regulation and age-related alteration of ChAT activity in different parts of the brain. Moreover the effect of Abeta peptides on ChAT activity in adult and aged brain was investigated. The enzyme activity was determined in the brain cortex, hippocampus and striatum in adult (4-months-old), adult-aged (14-months-old) and aged (24-months-old) animals. The highest ChAT activity was observed in the striatum. We found that inhibitors of protein kinase C, A, G and phosphatase A2 have no effect on ChAT activity and that this enzyme is not dependent on calcium ions. About 70% of the total ChAT activity is present in the cytosol. Arachidonic acid significantly inhibited cytosolic form of this enzyme. In the brain cortex and striatum from aged brain ChAT activity is inhibited by 50% and 37%, respectively. The aggregated form of Abeta 25-35 decreased significantly ChAT activity only in the aged striatum and exerted inhibitory effect on this enzyme in adult, however, statistically insignificant. ChAT activity in the striatum was diminished after exposure to 1 mM H2O2. The results from our study indicate that aging processes play a major role in inhibition of ChAT activity and that this enzyme in striatum is selectively sensitive for amyloid beta peptides.
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Affiliation(s)
- Agata Zambrzycka
- Department of Cellular Signaling, Medical Research Centre, Polish Academy of Sciences, Warsaw
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17
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Issa AM, Gauthier S, Collier B. Enzyme activity and protein of multiple forms of choline acetyltransferase: effects of calyculin A and okadaic acid. Neurochem Res 1999; 24:987-93. [PMID: 10478937 DOI: 10.1023/a:1021096408174] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Choline acetyltransferase (ChAT) appears to exist in multiple forms, three of which can be isolated biochemically as cytosolic (cChAT), ionically-membrane bound (ibChAT) and non-ionic membranous (mChAT). In this study, we first examined whether the quantitative distribution of enzyme protein and enzyme activity was the same. Enzyme activity and ChAT protein distributed similarly: the majority of ChAT activity and protein were found in cChAT followed by mChAT and least activity and amount were in ibChAT. Our second objective was to investigate the effects of calyculin A or okadaic acid on the subcellular distribution of ChAT activity and amount from rat hippocampal formation. Calyculin A and okadaic acid decreased significantly (p < 0.01) cytosolic and membranous ChAT activity; ionically-bound ChAT was not significantly (p > 0.67) different from control. Removal of calyculin A or okadaic acid restored cytosolic ChAT activity (p > 0.9 as compared to control), but not membranous enzyme activity (p < 0.05 as compared to control). The immunoreactive cytosolic ChAT was reduced significantly (p < 0.01) by calyculin A and okadaic acid. Enzyme amount of membranous ChAT was decreased significantly by calyculin A (p < 0.01) and okadaic acid (p < 0.001). Enzyme amount of ionically-bound ChAT was not changed (p > 0.99) by either of these two phosphatase inhibitors. This investigation demonstrates that alterations in ChAT activity of each subfraction parallel changes in enzyme amounts in the same fractions.
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Affiliation(s)
- A M Issa
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada
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18
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Resendes MC, Dobransky T, Ferguson SS, Rylett RJ. Nuclear localization of the 82-kDa form of human choline acetyltransferase. J Biol Chem 1999; 274:19417-21. [PMID: 10383456 DOI: 10.1074/jbc.274.27.19417] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Choline acetyltransferase is the enzyme catalyzing synthesis of the neurotransmitter acetylcholine in cholinergic neurons. In human, transcripts encoding two forms of the enzyme with apparent molecular masses of 69 and 82 kDa are found in brain and spinal cord; the 82-kDa form differs from the 69-kDa enzyme only in terms of a 118-amino acid extension on its amino terminus. Using green fluorescent protein-tagged choline acetyltransferase, we show that the 82-kDa enzyme is targeted to nuclei of cells, whereas the 69-kDa protein is found in cytoplasm. Expression of site-directed and deletion mutants of the 82-kDa isoform reveals that the extended amino terminus contains a nuclear localization signal in the first nine amino acids which targets the protein to nucleus. This represents the first report of a neurotransmitter-synthesizing enzyme that is localized to the cell nucleus.
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Affiliation(s)
- M C Resendes
- Department of Physiology, The University of Western Ontario and the Neurodegenerative Diseases Group, The John P. Robarts Research Institute, London, Ontario N6A 5C1, Canada
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19
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Cooke LJ, Rylett RJ. Inhibitors of serine/threonine phosphatases increase membrane-bound choline acetyltransferase activity and enhance acetylcholine synthesis. Brain Res 1997; 751:232-8. [PMID: 9099809 DOI: 10.1016/s0006-8993(96)01183-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The present investigation examines the effects of phosphatase inhibition on short-term regulation of cholinergic function, with particular emphasis on choline acetyltransferase, the enzyme which synthesizes acetylcholine. Rat hippocampal synaptosomes were treated with either okadaic acid (10 nM) or calyculin-A (50 nM) to inhibit protein phosphatases 1 and 2A for 20 min prior to subfractionation of nerve terminals and measurement of choline acetyltransferase activity, or quantification of high-affinity choline transport and acetylcholine synthesis. Inhibition of synaptosomal phosphatases did not alter total or salt-soluble choline acetyltransferase activity, but membrane-bound and water-soluble forms of the enzyme were selectively increased in okadaic acid-treated nerve terminals to 129 +/- 11% and 137 +/- 10% of control, respectively. High-affinity choline transport was reduced to 77 +/- 6% and 76 +/- 7% of control in calyculin-A- and okadaic acid-treated nerve terminals, respectively. Acetylcholine synthesis was reduced to 73 +/- 6% of control in calyculin-A-treated synaptosomes only; acetylcholine synthesis was at control levels in okadaic acid-treated cultures correlating with enhanced choline acetyltransferase activity in the water-soluble and nonionically membrane-bound fractions. These investigations indicate a role for phosphoprotein phosphatases in the regulation of acetylcholine synthesis in the cholinergic nerve terminal. The observed increases in choline acetyltransferase activity in two subcellular fractions appears to compensate for decreased choline precursor availability, allowing acetylcholine synthesis to be maintained at control levels. The uncoupling of choline transport and acetylcholine synthesis in this situation represents a unique functional role for a subfraction of choline acetyltransferase.
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Affiliation(s)
- L J Cooke
- Department of Physiology, The University of Western Ontario, London, Canada
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20
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Schmidt BM, Rylett RJ. Basal synthesis of acetylcholine in hippocampal synaptosomes is not dependent upon membrane-bound choline acetyltransferase activity. Neuroscience 1993; 54:649-56. [PMID: 8392667 DOI: 10.1016/0306-4522(93)90236-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Choline acetyltransferase, the enzyme which catalyses the formation of acetylcholine within cholinergic nerve terminals, exists in both cytosolic and membrane-associated subcellular pools. In the present study, alteration in nerve terminal Cl- homeostasis was used as an experimental tool to elucidate the role of membrane-bound choline acetyltransferase in regulation of the biosynthesis of acetylcholine in rat hippocampal synaptosomes under basal or resting conditions. Reduction of extracellular Cl- concentration from 131 to 48 mM through iso-osmotic replacement with isethionate ions produced a selective decrease, to approximately 50% of control, of nerve terminal membrane-associated choline acetyltransferase activity. Under these experimental conditions, there were no changes in the activity of cytosolic enzyme or high-affinity choline uptake, or in acetylcholine synthesis. Replacement of medium Cl- with Br- supported maintenance of synaptosomal membrane-bound choline acetyltransferase activity better than did I- or isethionate ions; high-affinity choline uptake activity and acetylcholine synthesis were affected similarly. Incubation of synaptosomes with low concentrations of the Cl- channel blockers 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid (50 microM) and niflumic acid (100 microM) selectively decreased activity of the membrane-bound enzyme, with no effect on cytosolic choline acetyltransferase or high-affinity choline uptake activities. Acetylcholine synthesis was unchanged, even though membrane-bound choline acetyltransferase activity was decreased in some samples (250 microM 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid) to about 10% of control. Experimental manipulations designed to alter neuronal Cl- homeostasis resulted in selective changes in membrane-bound choline acetyltransferase activity, thereby allowing the first direct examination of its physiological role in regulation of acetylcholine synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- B M Schmidt
- Department of Physiology, University of Western Ontario, London, Canada
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21
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Salem N, Medilanski J, Pellegrinelli N, Eder-Colli L. The proportion of amphiphilic choline acetyltransferase in Drosophila melanogaster is higher than in rat or Torpedo and is developmentally regulated. Brain Res 1993; 609:223-30. [PMID: 8508306 DOI: 10.1016/0006-8993(93)90876-o] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We show that in the central nervous system of the fly, Drosophila melanogaster, choline acetyltransferase (ChAT) activity exists under two molecular forms, a soluble, hydrophilic form and a membrane-bound, amphiphilic form. This is based on the following demonstrations of differential solubilization and interaction with non-denaturing detergents: sequential extraction of Drosophila heads produced low-salt-soluble (83-87%) and detergent-soluble (6-7%) ChAT activity. Sedimentation in sucrose gradients of detergent-soluble ChAT was found to be influenced by the type of detergent present in the gradient (Triton X-100 and Brij 96). This was not the case for low-salt-soluble ChAT. To further confirm these findings, we subjected Drosophila heads to Triton X-114 fractionation. This method, which yielded 12% of amphiphilic ChAT activity, separates hydrophilic from amphiphilic proteins. Compared to central nervous tissue of rat and Torpedo electric lobes, Drosophila head contained the highest proportion of amphiphilic ChAT activity. Synaptosomes isolated from Torpedo electric organ exhibited higher levels of amphiphilic ChAT than did electric lobes. Of the three animal species analyzed here, the Torpedo amphiphilic enzyme was the most hydrophobic and the rat enzyme the least hydrophobic. The proportion of amphiphilic ChAT was analyzed during Drosophila development. The percentage of this activity increased about 7 times from embryo to larva and then remained constant until the adult fly age.
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Affiliation(s)
- N Salem
- Department of Pharmacology, Centre Médical Universitaire, Geneva, Switzerland
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22
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Collier B, Tandon A, Prado MA, Bachoo M. Storage and release of acetylcholine in a sympathetic ganglion. PROGRESS IN BRAIN RESEARCH 1993; 98:183-9. [PMID: 8248507 DOI: 10.1016/s0079-6123(08)62397-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- B Collier
- Department of Pharmacology and Therapeutics, McGill University, Canada
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23
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Eder-Colli L, Briand PA, Dunant Y. Membrane-bound choline acetyltransferase of the torpedo has characteristics of an integral membrane protein and can be solubilized by proteolysis. Brain Res 1992; 573:284-92. [PMID: 1504766 DOI: 10.1016/0006-8993(92)90774-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Due to Triton X-114 fractionation of synaptosomes isolated from the electric organ of the fish Torpedo, the existence of a hydrophilic and an amphiphilic form of the enzyme choline-O-acetyltransferase (ChAT) was revealed. Amphiphilic ChAT which represents about 10% of total enzyme activity in synaptosomes, reached 40% of ChAT activity measured in preparations of synaptosomal plasma membranes (SPM) which were washed with solutions of increasing ionic strength. ChAT activity bound to washed SPM could be partially solubilized using proteinase K but not phospholipase C. No ChAT solubilization occurred by treating intact synaptosomes with proteinase K. Water/Triton X-114 partition coefficients of hydrophilic and amphiphilic ChAT were found to be 6.5 and 0.17, respectively. Sedimentation coefficients determined by centrifugation in linear density gradients of sucrose containing Triton X-100, were 4.2S and 4.4S for amphiphilic and hydrophilic ChAT, respectively. On the other hand, removal of Triton X-114 from the detergent phase containing amphiphilic ChAT activity led to enzyme aggregation. Finally, amphiphilic ChAT was slightly more acidic (pH 6.6) than was hydrophilic enzyme (6.8-7.0). We conclude that in Torpedo synaptosomes two forms of ChAT activity, a soluble and a membrane-bound form, are indeed present which differ in their hydrophobicity. The soluble form is hydrophilic. The membrane-bound form is amphiphilic and it aggregates upon removal of detergent. These are two characteristics of integral membrane proteins. Membrane-bound ChAT is most probably intracellularly oriented and not bound to membrane through a 'receptor' protein.
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Affiliation(s)
- L Eder-Colli
- Department of Pharmacology, Centre Médical Universitaire, Geneva, Switzerland
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24
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Wessler I. Acetylcholine at motor nerves: storage, release, and presynaptic modulation by autoreceptors and adrenoceptors. INTERNATIONAL REVIEW OF NEUROBIOLOGY 1992; 34:283-384. [PMID: 1587718 DOI: 10.1016/s0074-7742(08)60100-2] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- I Wessler
- Department of Pharmacology, University of Mainz, Germany
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25
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Eder-Colli L, Froment Y, Monsurro MR. Direct inhibition of choline acetyltransferase activity by a monoclonal antibody raised against the plasma membrane of cholinergic nerve terminals. Brain Res 1989; 500:90-8. [PMID: 2605511 DOI: 10.1016/0006-8993(89)90302-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A monoclonal antibody raised against cholinergic synaptosomal plasma membranes isolated from Torpedo electric organ, inhibited completely amphiphilic and hydrophilic choline acetyltransferase (ChAT) activities extracted and separated by using Triton X-114 phase partition of synaptosomes. We tested whether ChAT inhibition was direct or not. We found that the antibody was inhibiting ChAT in preparations of very low purity as well as ChAT that was immunoprecipitated by using a non-inhibitory anti-ChAT polyclonal antibody. Also, inclusion of acetylcoenzyme A at 20 times its Km during incubation of ChAT and antibody, completely prevented ChAT inhibition. This same concentration of the ChAT substrate could significantly but not completely dissociate the complex enzyme-antibody. These results spoke in favour of a direct inhibition of ChAT; the antibody most probably binds to an epitope that may be located at or near the acetylcoenzyme A binding site. The inhibitory effect on hydrophilic and amphiphilic ChAT was dependent on the antibody concentration, but amphiphilic activity required higher concentrations to be affected to the same extent as hydrophilic activity. This was found not only with Torpedo, but also with rat and human ChAT activities. Thus, the antibody appears to be able to distinguish the two forms of ChAT activity.
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Affiliation(s)
- L Eder-Colli
- Department of Pharmacology, Centre Médical Universitaire, Geneva, Switzerland
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26
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Abstract
Human placental Choline Acetyltransferase (ChAT) has been shown to be phosphorylated in vitro by kinases present in rat brain. Phosphorylation occurs at a single site with the exclusive phosphoamino acid being serine. ChAT phosphorylation was shown to be calcium, and not cyclic nucleotide, dependent and was inhibited by inhibitors of calcium/calmodulin protein kinases including anti-calmodulin anti-sera. ChAT phosphorylation was stimulated by calmodulin (9 fold) and, to a lesser extent, by phosphatidylserine (4 fold). These results indicate the involvement of a calcium/calmodulin and possibly also a calcium/phospholipid kinase. This finding was confirmed by demonstrating ChAT phosphorylation using both purified multifunctional calcium/calmodulin protein kinase (CaMK) and calcium/phospholipid protein kinase C (PKC) from rat brain. A stoichiometric incorporation of 0.9 mol phosphate/mol ChAT was achieved by CaMK. Phosphorylated ChAT could be isolated from freshly prepared rat brain synaptosomes. The results obtained with this model system support the hypothesis that in vivo a fraction of ChAT exists phosphorylated.
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Affiliation(s)
- G Bruce
- Department of Biochemistry, University of Texas, Dallas 75235
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27
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Mykita S, Collier B. Acetylcholine synthesis by a sympathetic ganglion in the presence of 2-(4-phenylpiperidino)cyclohexanol (AH5183) and picrylsulfonic acid. J Neurochem 1989; 52:1686-93. [PMID: 2723629 DOI: 10.1111/j.1471-4159.1989.tb07245.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The present experiments measured the release and the synthesis of acetylcholine (ACh) by cat sympathetic ganglia in the presence of 2-(4-phenylpiperidino)cyclohexanol (AH5183 or vesamicol) and/or picrylsulfonic acid (TNBS), two compounds known to have the ability to block the uptake of ACh by cholinergic synaptic vesicles in vitro. We confirmed that, in stimulated (5 Hz) perfused (30 min) ganglia, AH5183 depressed ACh release and ACh tissue content increased by 86 +/- 6% compared to contralateral ganglia used as controls. Preganglionic activity increased ACh release by a similar amount in the presence (19.9 +/- 1.0 pmol/min) or absence (20.5 +/- 2.4 pmol/min) of TNBS. The final tissue ACh content was also similar in the presence (1,668 +/- 166 pmol) or absence (1,680 +/- 56 pmol) of TNBS. However, the AH5183-induced increase of tissue ACh content (86 +/- 6%) was abolished completely when AH5183 was perfused with 1.5 mM TNBS (-3.0 +/- 1.0%). This inhibition of ACh synthesis, observed in TNBS-AH5183-perfused ganglia, was not dependent upon further inhibition of ACh release beyond that caused by AH5183 alone, because 14.0 +/- 1.9% of the transmitter store was released by preganglionic nerve stimulation in the presence of TNBS plus AH5183 and this was similar in the presence of AH5183 without TNBS (14.0 +/- 0.6%). Moreover, when ganglia were first treated with TNBS and then stimulated in the presence of AH5183, an increase of 64 +/- 6% of the ganglionic ACh content occurred, and this increase was not statistically different from the increase measured with AH5183 alone (86 +/- 6%).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- S Mykita
- Department of Pharmacology and Therapeutics, McGill University, Montreal, Canada
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28
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Rylett RJ. Synaptosomal "membrane-bound" choline acetyltransferase is most sensitive to inhibition by choline mustard. J Neurochem 1989; 52:869-75. [PMID: 2918313 DOI: 10.1111/j.1471-4159.1989.tb02535.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The objectives of the present study were to validate the presence of cytoplasmic and membrane-associated pools of choline acetyltransferase (ChAT) in rat brain synaptosomes, and to evaluate inhibition of these different forms of the enzyme by the nitrogen mustard analogue of choline, choline mustard aziridinium ion (ChM Az). The relative distribution of ChAT and lactate dehydrogenase (LDH) was followed in subfractions of synaptosomes to establish whether ChAT activity associated with salt-washed presynaptic membranes represents membrane-bound protein rather than cytosolic enzyme trapped within undisrupted synaptosomes or revesiculated membrane fragments. The percentage of total synaptosomal ChAT activity (14%) recovered in the final membrane pellet always exceeded that of LDH (6%), lending support to the hypothesis that much of the ChAT associated with the membranes was a membrane bound form of the enzyme. Incubation of purified synaptosomes with ChM Az led to irreversible inhibition of ChAT activity; this loss of enzyme activity could not be accounted for by lysis of nerve terminals during incubation in the presence of the mustard analogue. Subfractionation of the ChM Az-treated nerve terminals revealed that the membrane-bound form of ChAT was inhibited to the greatest extent, followed by the ionically membrane-associated enzyme, with the activity of the water-solubilized enzyme not differing significantly from control. Preparation of the synaptosomal ChAT subfractions from untreated nerve terminals prior to incubation with varying concentrations of ChM Az or naphthylvinylpyridine revealed that under these conditions water-solubilized, ionically membrane-associated, and detergent-solubilized membrane-bound pools of ChAT were not differentially inhibited by either compound.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R J Rylett
- Department of Physiology, University of Western Ontario, London, Canada
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29
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Toledo A, Sabriá J, Rodriguez R, Brandner R, Rodriguez J, Palacios JM, Blanco I. Properties and ontogenic development of membrane-bound histidine decarboxylase from rat brain. J Neurochem 1988; 51:1400-6. [PMID: 3171585 DOI: 10.1111/j.1471-4159.1988.tb01104.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Histidine decarboxylase (HD) activity was determined in high-speed fractions (100,000 g for 60 min) obtained from whole rat brain homogenates. Twenty-eight percent of the HD activity was associated with membranes, and the remaining was soluble. Several properties of the soluble and membrane-bound HD were compared. No significant differences in the values of Km for histidine and pyridoxal 5'-phosphate were observed. The solubilization of membrane-bound HD with Triton X-100 resulted in an increase of 60% over the nonsolubilized activity with no changes in the Km for substrate and cofactor. The proportion of free pyridoxal 5'-phosphate-independent activity was identical in both fractions. The soluble and membrane-bound forms of the enzyme differ slightly in their pH-activity profiles, although both enzymes showed an optimum pH near 6.5. The HD activities present in soluble and membrane fractions were determined at different postnatal ages. The soluble activity increased until day 90, whereas the membrane-bound activity became stabilized from day 20.
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Affiliation(s)
- A Toledo
- Departamento Bioquimica y Biologia Molecular, Facultad de Medicina, Universidad Autónoma de Barcelona, Spain
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Carroll PT, Ivy MT. Effect of 2-(4-phenylpiperidino)cyclohexanol (AH 5183) on the veratridine-induced increase in acetylcholine synthesis by rat hippocampal tissue. J Neurochem 1988; 51:808-19. [PMID: 3411328 DOI: 10.1111/j.1471-4159.1988.tb01816.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The intent of this study was to determine whether the drug 2-(4-phenylpiperidino)cyclohexanol (AH 5183 or vesamicol) might inhibit the veratridine-induced increase in acetylcholine (ACh) synthesis by reducing the veratridine-induced activation of a detergent-soluble choline-O-acetyltransferase (EC 2.3.1.6; ChAT) fraction associated with a vesicle-bound store of ACh. When minces of rat hippocampal tissue were loaded with [14C]choline and subsequently depolarized with veratridine, an increase in the synthesis of [14C]ACh occurred that could be abolished by L-AH 5183 (75 nM). When minces were depolarized with veratridine in the presence of L-AH 5183 (75 nM), the depolarization-induced activation of a detergent-soluble ChAT fraction associated with a vesicle-bound store of ACh was blocked. Conversely, the veratridine-induced activation of a water-soluble ChAT fraction believed to be cytosolic was not. AH 5183 also blocked the repletion of the vesicle-bound store with newly synthesized ACh following veratridine-induced depletion of ACh, a result that appeared to be mediated by an effect on the synthesis of ACh at the vesicular surface. These results suggest that veratridine depolarization of rat hippocampal nerve terminals stimulates the synthesis of ACh by activating a detergent-soluble fraction of ChAT closely associated with synaptic vesicle release sites. ACh synthesis and transport at the vesicular surface may be influenced by a common AH 5183-sensitive regulatory protein.
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Affiliation(s)
- P T Carroll
- Department of Pharmacology, Texas Tech University Health Sciences Center, Lubbock 79430
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31
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Eder-Colli L, Amato S, Froment Y. Amphiphilic and hydrophilic forms of choline-O-acetyltransferase in cholinergic nerve endings of the Torpedo. Neuroscience 1986; 19:275-87. [PMID: 3785667 DOI: 10.1016/0306-4522(86)90021-7] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
In the purely cholinergic nerve endings isolated (i.e. synaptosomes) from the electric organ of the fish Torpedo, the enzyme choline acetyltransferase was found to exist not solely in its well-known soluble form but also in a form which is non-ionically bound to the plasma membrane; this activity could not be solubilized in solutions of high ionic strength (0.5 M NaCl). The non-ionic detergent Triton X-114 was used to solubilize synaptosomes isolated from either the electric organ of Torpedo or rat brain. This detergent allows to separate hydrophilic from amphiphilic proteins of cells or subcellular fractions. Twelve per cent of the synaptosomal choline acetyltransferase partitioned as amphiphilic and 80-97% as hydrophilic activity. The percentage of amphiphilic activity present in synaptosomes was significantly higher than that of the form of activity (4.4%) extracted from samples containing only the soluble form of choline acetyltransferase but was significantly lower than the percentage of amphiphilic enzyme present in preparations of synaptosomal plasma membrane (20-22%) which were enriched in the non-ionically membrane-bound form of choline acetyltransferase. These results indicate that the soluble and the non-ionically membrane-bound enzymes differ in their capacity to interact with non-ionic detergents. The preparations of synaptosomal plasma membranes contained significantly higher proportions of detergent-insoluble choline acetyltransferase activity than did the whole synaptosomes; the difference was more striking for the Torpedo than for the rat enzyme. This detergent-insoluble activity was not due to aggregates of the enzyme. Some properties of the hydrophilic and amphiphilic choline acetyltransferase of Torpedo were analyzed. The two forms of the enzyme did not exhibit different affinities for their substrates; they were found to differ with respect to their sensitivity to inhibition by increasing concentrations of the two products of the reaction, acetylcholine and coenzyme A and heat inactivation at 45 degrees C. Most probably the hydrophilic and amphiphilic activities correspond to what was referred to as soluble and non-ionically membrane-bound choline acetyltransferase, respectively. The amphiphilic form may be an integral enzyme of the plasma membrane of cholinergic nerve endings or may be tightly bound to a specific protein in this membrane which may act as a "receptor" for choline acetyltransferase.
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32
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Badamchian M, Morrow K, Carroll PT. Immunological, isoelectric, hydrophobic and molecular weight differences between soluble and ionically membrane-bound fractions of choline-o-acetyltransferase prepared from mouse and rat brain. Neurochem Int 1986; 9:409-21. [DOI: 10.1016/0197-0186(86)90083-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/1985] [Accepted: 03/24/1986] [Indexed: 10/27/2022]
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33
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Bruce G, Wainer BH, Hersh LB. Immunoaffinity purification of human choline acetyltransferase: comparison of the brain and placental enzymes. J Neurochem 1985; 45:611-20. [PMID: 4009177 DOI: 10.1111/j.1471-4159.1985.tb04030.x] [Citation(s) in RCA: 186] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
A rapid and efficient immunoaffinity purification procedure has been developed for human placental choline acetyltransferase (ChAT). Using this procedure, human placental ChAT was purified to homogeneity with high recovery of enzyme activity (50-60%). Purified ChAT was used to raise a monospecific anti-human ChAT polyclonal antibody in rabbits. A comparison of the physical properties of ChAT was made between the enzymes purified from human brain and human placenta. Only one form of the enzyme exists in either tissue, having identical molecular weights of 68,000 and a single apparent pI of 8.1. A more detailed comparison of the two enzymes using peptide mapping and epitope mapping indicates identity between the brain and placental enzymes.
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Butterfield DA, Nicholas MM, Markesbery WR. Evidence for an increased rate of choline efflux across erythrocyte membranes in Alzheimer's disease. Neurochem Res 1985; 10:909-18. [PMID: 4047285 DOI: 10.1007/bf00964628] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Alzheimer's disease (AD), the major dementing disorder of the elderly, is associated with cholinergic neuronal loss and decreased activity of choline acetyltransferase (CAT). Previous biophysical studies had suggested an altered conformation of membrane proteins in AD erythrocyte ghosts. Since erythrocytes have a choline transport system and cholinergic neurons are implicated in AD, the present experiments were undertaken to determine if the efflux rate of [14C]choline was altered in AD erythrocytes. The mean efflux rate constant was highly significantly increased (P less than 0.01) by greater than 25% in 9 drug-free AD patients compared to 9 sex-matched, drug-free controls of similar age. These results are discussed in terms of potential molecular mechanisms to account for cholinergic neuronal loss in AD.
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Eder-Colli L, Amato S. Membrane-bound choline acetyltransferase in Torpedo electric organ: a marker for synaptosomal plasma membranes? Neuroscience 1985; 15:577-89. [PMID: 4022340 DOI: 10.1016/0306-4522(85)90235-0] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The enzyme choline-O-acetyltransferase catalyses the biosynthesis of acetylcholine from acetyl coenzyme A and choline and is considered as one of the best markers for cholinergic nerve endings. The distribution of this enzymatic activity was analysed during the purification of plasma membranes of purely cholinergic nerve endings isolated from the electric organ of the fish Torpedo marmorata. This tissue, which receives a profuse and purely cholinergic innervation, can be considered as being a "giant" neuromuscular synapse. The isolated nerve endings (synaptosomes) were first osmotically disrupted and their plasma membranes isolated by equilibrium density centrifugation (discontinuous followed by continuous sucrose gradients). Choline acetyltransferase activity was found to exist in three forms: (1) a soluble form (the major one) present in the cytoplasm of the nerve endings, (2) a form which is ionically associated with membranes and which can be solubilized by washing exhaustively the membrane fraction with solutions of high ionic strength (0.5 M NaCl) and (iii) a form which is non-ionically bound to membranes and cannot be solubilized with high salt solution. The soluble and the non-ionically bound activities exhibited very similar affinities for choline (1.34 and 1.64 mM, respectively). The non-ionically membrane-associated form of choline acetyltransferase was found to "copurify" with the cholinergic synaptosomal plasma membranes of Torpedo, its specific activity being increased from 122 (crude fraction) to 475 (purified membrane fraction) nmol/h/mg protein. An enrichment was also observed for another cholinergic marker, the enzyme acetylcholinesterase, but not for the nicotinic receptor to acetylcholine, a marker for postsynaptic membranes. No choline acetyltransferase activity could be detected in preparations of synaptic vesicles that were highly purified from the electric organ. Also, the non-ionically associated form of choline acetyltransferase activity was hardly detectable (2.4 nmol/h/mg protein) in fractions enriched in axonal membranes prepared from the cholinergic electric nerves innervating the electric organ. The partition into soluble and membrane-bound activity was also analysed for choline acetyltransferase present in human placenta, a rich source for the enzyme but a non-innervated tissue. In this case the great majority of the enzyme appeared as soluble activity. Very low levels of non-ionically membrane-bound activity were found to be present in a crude membrane fraction from human placenta (2.8 nmol/h/mg protein).(ABSTRACT TRUNCATED AT 400 WORDS)
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Abstract
A nitrogen phosphorus-gas chromatographic procedure was modified to determine the extent of in vivo acetylation of the choline analogs homocholine and beta-methylcholine. Infusion of homocholine (18 mumoles) for 2 hours into the lateral ventricle of the rat produced 2.3 nmoles/gram of acetylhomocholine which represented 0.035% of the detected homocholine. Infusion of the same quantity of beta-methylcholine produced 1.0 nmole/gram of acetyl-beta-methylcholine representing 0.025% of the detected beta-methylcholine. Although pretreatment with hemicholinium-3 reduced the amount of acetylated product formed from either analog, the reduction was significant only for acetyl-beta-methylcholine (p less than 0.01).
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Carroll PT. Veratridine-induced release of acetylcholine from mouse forebrain minces: dependence on the hydrolysis of cytoplasmic acetylcholine for a source of choline. Brain Res 1984; 321:55-62. [PMID: 6498514 DOI: 10.1016/0006-8993(84)90680-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The importance of depolarization induced hydrolysis of cytoplasmic acetylcholine (ACh) in providing choline for the veratridine-and high K+-induced release of acetylcholine was studied in mouse forebrain minces. Results indicated that a loss of hydrolyzable cytoplasmic ACh prior to depolarization reduced the amount of ACh released by veratridine but not the amount released by high K+. The reduction in the veratridine-induced release of ACh did not occur during the first 5 min of incubation. Loss of vesicular ACh prior to depolarization reduced both the veratridine- and K+-induced release of ACh during the first 5 min of incubation. Blockade of extra-cellular choline transport by hemicholinium (HC-3) did not affect the veratridine-induced release of ACh during a 10 min incubation period unless the cytoplasmic pool of ACh had first been depleted and was unavailable as a source of choline. In contrast, HC-3 reduced the K+-induced release of ACh from brain tissue with normal stores of cytoplasmic ACh. These results indicate that both depolarizing agents primarily stimulate the release of preformed ACh from a vesicular fraction during the first 5 min of mince incubation. Thereafter, they both stimulate the release of newly synthesized ACh, however, they differ in one important respect. The principal source of choline for the veratridine-induced release of newly synthesized ACh appears to be the cytoplasmic pool of ACh, whereas the major source of choline for the K+-induced release of newly synthesized ACh appears to be extracellular choline.
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Benishin CG, Carroll PT. Developmental differences between soluble and membrane-bound fractions of choline-O-acetyltransferase in neonatal mouse brain. J Neurochem 1984; 43:885-7. [PMID: 6747640 DOI: 10.1111/j.1471-4159.1984.tb12815.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Three fractions (one soluble and two membrane-bound) of choline acetyltransferase (ChAT) isolated from a nerve ending fraction of mouse forebrain, which have previously been reported to differ in several biochemical and physical aspects, were also found to differ in their rates of postnatal development. At 2 days of age, the activity in all three fractions was very low. Sodium phosphate buffer-soluble (cytoplasmic) ChAT activity increased significantly by 8 days of age, whereas the ChAT activity of the two membrane-bound fractions (NaCl- and Triton-soluble) did not increase until 13 days of age. These results suggested that the differences observed between the three fractions of ChAT prepared from mouse brain are not solely artifacts of the isolation procedure.
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Mantione CR, Fisher A, Hanin I. Possible mechanisms involved in the presynaptic cholinotoxicity due to ethylcholine aziridinium (AF64A) in vivo. Life Sci 1984; 35:33-41. [PMID: 6330483 DOI: 10.1016/0024-3205(84)90149-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
AF64A is a toxin which can diminish irreversibly cholinergic transmission in vivo (1, 2). Disruption of neurotransmitter function in vivo is specific to the cholinergic system when AF64A is administered in nanomolar quantities (3, 4). The mechanisms involved appear to be mediated presynaptically (g). The neurochemical and behavioral consequences of AF64A administration are reminiscent of similar measures in patients with Alzheimer's disease (5, 6). Consequently, we have suggested tentatively that the AF64A treated animal may be explored as a potential animal model of this debilitating disease state (7). In this report we provide a brief overview of our recent findings using this compound in vivo, attempt to correlate these findings with those of others with similar aziridinium agnts in vitro, and propose a possible mechanism of action of AF64A in vivo, based on recent observations made in our laboratories.
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Abstract
Two cyclic choline analogues (3-hydroxy-N,N- dimethylpiperidinium and 2-hydroxymethyl-N,N- dimethylpiperidinium ) and two cyclic homocholine analogues (4-hydroxy-N,N- dimethylpiperidinium and 3-hydroxymethyl-N,N- dimethylpiperidinium ) have been studied with regard to their actions at the cholinergic synapse. All the analogues had some direct depolarizing activity on the frog rectus abdominis muscle but they were less potent in this respect than acetylcholine. Compared to physostigmine, the analogues were weak inhibitors of cholinesterase enzymes. All the analogues were found to have a presynaptic blocking action on the rat phrenic nerve-hemidiaphragm preparation, which was reversed by choline. In addition, they all inhibited the high affinity transport of choline into synaptosomes but only the cyclic choline analogues were found to be acetylated by soluble choline acetyltransferase in vitro. We conclude that the hydroxypiperidinium analogues caused the presynaptic block seen at the neuromuscular junction by inhibiting acetylcholine synthesis.
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Carroll PT, Benishin CG. Depolarization of mouse forebrain minces with veratridine and high K+: failure to stimulate the Ca2+ independent, spontaneous release of acetylcholine from the cytoplasm due to hydrolysis of the acetylcholine stored there. Brain Res 1984; 291:261-72. [PMID: 6697191 DOI: 10.1016/0006-8993(84)91258-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Both high K+ and veratridine, depolarizing agents with different mechanisms of action, lowered the ACh content of the cytoplasmic (S3) fraction of mouse forebrain minces incubated in a Ca2+-free Krebs solution, without stimulating ACh release or altering the level of ACh in the vesicle-bound (P3) fraction. Veratridine increased the level of choline in the P3 fraction by the same amount as it reduced the level of ACh in the S3 fraction, and these changes did not occur in the presence of tetrodotoxin (TTX). Pretreatment of minces in normal Krebs increased the ACh but not the choline content of the S3 fraction. Following this expansion of the S3 ACh content, veratridine caused an even greater loss of S3 ACh, and increased the Ca2+-independent release of ACh slightly. Under these conditions, veratridine also stimulated the Ca2+ independent release of choline, and this increase exceeded that obtained for the Ca2+-independent release of ACh. Preincubation in normal Krebs with paraoxon did not alter the S3 ACh content after 5 min, but raised it by 78% after 30 min. Under the latter conditions of pretreatment, veratridine then stimulated the Ca2+-independent release of ACh even more, but did not stimulate the release of choline. These results suggest that depolarization of brain tissue does not facilitate the Ca2+-independent release of ACh from the cytoplasm because a portion of ACh stored there is hydrolyzed. When the cytoplasmic level of ACh is sufficiently elevated prior to depolarization, then some ACh escapes hydrolysis and is released independently of Ca2+. It is suggested that the depolarization-induced hydrolysis of cytoplasmic ACh may be mediated by an intraterminal form of AChE and may, in addition to the hydrolysis of extracellular ACh, provide substrate for the formation and release of ACh by the vesicle-bound fraction.
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Tucek S. Problems in the organization and control of acetylcholine synthesis in brain neurons. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1984; 44:1-46. [PMID: 6385131 DOI: 10.1016/0079-6107(84)90011-7] [Citation(s) in RCA: 112] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Benishin CG, Carroll PT. Multiple forms of choline-O-acetyltransferase in mouse and rat brain: solubilization and characterization. J Neurochem 1983; 41:1030-9. [PMID: 6619842 DOI: 10.1111/j.1471-4159.1983.tb09047.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Three forms of acetyl coenzyme A: choline-O-acetyltransferase (EC 2.3.1.6, ChAT) have been isolated from mouse and rat forebrain synaptosomes with a 100 mM sodium phosphate (NaP) buffer of pH 7.4, a high-salt solution (500 mM NaCl), and a 2% Triton DN-65 solution, respectively. The Triton-solubilized form of ChAT differed from the other two forms in its capacity to acetylate homocholine, its pH profile, and its sensitivity to denaturation. NaCl-solubilized ChAT could be distinguished from the other two forms with respect to pH profile, sensitivity to inhibition by 4-(1-naphthylvinyl) pyridine (in the presence of Triton), and apparent Km value for choline acetylation. The caudate and putamen of rat brain contained the highest amount of ChAT activity, based on tissue wet weight, and the cerebellum contained the least of the brain regions examined; only the cerebellum had more membrane-bound than soluble ChAT. Septal lesion reduced ChAT activity in the NaP- and Triton-solubilized fractions prepared from hippocampus by 68% and 64%, respectively, whereas it reduced the activity of the NaCl-solubilized fraction by only 21%. These results suggest that three different forms of ChAT may exist in both mouse and rat brain.
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Levey AI, Rye DB, Wainer BH. Immunochemical studies of bovine and human choline-O-acetyltransferase using monoclonal antibodies. J Neurochem 1982; 39:1652-9. [PMID: 7142993 DOI: 10.1111/j.1471-4159.1982.tb07999.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Immunochemical properties of bovine and human choline acetyltransferase (ChAT, EC 2.3.1.6, acetyl-CoA:choline-O-acetyltransferase) were studied using six monoclonal antibodies (AB1, AB5, AB6, AB7, AB8, and AB9) reactive with the enzyme. All antibodies except AB1 bound specifically to two proteins of 68,000 and 70,000 MW on "Western" blots of sodium dodecyl sulfate-polyacrylamide gels containing human or bovine ChAT. The enzyme was specifically absorbed to immobilized antibody and could not be eluted by low pH and/or high salt concentrations although the enzyme retained activity on the immunoabsorbent. Pure bovine enzyme consisting of the same two proteins as seen in the Western blotting studies was eluted from immobilized AB1 in the presence of sodium dodecyl sulfate. Although active enzyme could not be eluted from immobilized antibodies by standard conditions, various combinations of free and immobilized antibodies were effective in competing off bound enzyme. Free antibody AB1 quantitatively eluted the active enzyme from immobilized AB1. The different capacities of the antibodies to elute enzyme from various immunoabsorbents reflect interesting properties of both the enzyme and the antibodies.
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Meyer EM, Engel DA, Cooper JR. Acetylation and phosphorylation of choline following high or low affinity uptake by rat cortical synaptosomes. Neurochem Res 1982; 7:749-59. [PMID: 7121721 DOI: 10.1007/bf00965527] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Synaptosomal acetylcholine synthesis was found to be dependent on the presence of Na+-dependent HC-3 sensitive choline transport at low (5.5 mM) and high (35 mM) K+ concentrations. However, at 5, 20, and 100 microM choline, choline phosphorylation was proportional to total choline uptake, in the presence or absence or high affinity transport. Only in the presence of eserine (50 microM) did acetylcholine synthesis increase as the choline concentration was elevated from 20 microM to 100 microM, and this effect was observed at low and high K+ concentrations. Our results suggest that: 1) the synthesis of non-surplus synaptosomal ACh is dependent on high affinity choline transport; and 2) choline is equally likely to be phosphorylated after being taken up by low or high affinity transport.
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46
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Luqmani YA, Richardson PJ. Homocholine and short-chain N-alkyl choline analogues as substrates for Torpedo choline acetyltransferase. J Neurochem 1982; 38:368-74. [PMID: 7108543 DOI: 10.1111/j.1471-4159.1982.tb08638.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The kinetic parameters, Km and Vmax, for the acetylation of choline and several close analogues were determined by using (a) purified choline acetyltransferase and (b) a hypotonically lysed synaptosomal extract prepared from the electric organ of Torpedo marmorata. Whereas the Km for choline was similar in both cases (0.51 and 0.42 mM), the crude enzyme showed a three- to fivefold greater affinity for its analogues than the purified enzyme, the activity decreasing rapidly with increased N-alkyl substitution. Homocholine was a poor substrate, but was clearly acetylated by both preparations. The effect of salt on analogue acetylation by the crude enzyme was studied by increasing NaCl concentration from zero to 150 mM. There was an increase in both Km and Vmax for all substrates: choline, N,N,N-dimethylmonothylaminoethanol, -monomethyldiethylaminoethanol and -dimethylmonobutylaminoethanol showed the greatest changes, whilst N,N,N-triethylaminoethanol and -dimethylmonopropylaminoethanol and homocholine were much less affected However, in all cases, the kinetic parameter Vmax/Km remained unchanged. The maximal velocities of the different substrates varied more under conditions of high than of low salt. Sodium chloride up to 300 mM had no effect on the amount of enzyme which was bound to membranes in the synaptosomal extract. It is concluded that choline acetyltransferase has a high degree of substrate specificity, which is slightly altered by purification. The effects of salt cannot be explained as a consequence of nonspecific ionic association with membranes.
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Specific antibodies to bovine choline acetyltransferase raised in mice immunised with small amounts of partially purified enzyme. Neurochem Int 1982; 4:383-8. [DOI: 10.1016/0197-0186(82)90080-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/1982] [Accepted: 03/23/1982] [Indexed: 11/19/2022]
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Carroll PT, Aspry JA. Spontaneous and potassium-induced release of acetylcholine from mouse forebrain minces. Neuroscience 1981; 6:2555-9. [PMID: 6275298 DOI: 10.1016/0306-4522(81)90101-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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49
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Benishin CG, Carroll PT. Differential sensitivity of soluble and membrane-bound forms of choline O-acetyltransferase to inhibition by Coenzyme A. Biochem Pharmacol 1981; 30:2483-4. [DOI: 10.1016/0006-2952(81)90346-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Abstract
Samples of minced mouse forebrain were treated in a way that resulted in a high ratio of false cholinergic transmitter (acetylhomocholine) to true transmitter (acetylcholine) in a synaptic vesicle fraction, and a low ratio of false to true transmitter in the nerve terminal cytoplasm. The spontaneous release of cholinergic transmitters from this minced tissue occurred independently of calcium and had a ratio of false to true transmitter similar to that of the cytoplasm, whereas the evoked transmitter release required calcium and had a ratio of false to true transmitter similar to that of the vesicular fraction.
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