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Masuoka T, Uwada J, Kudo M, Yoshiki H, Yamashita Y, Taniguchi T, Nishio M, Ishibashi T, Muramatsu I. Augmentation of Endogenous Acetylcholine Uptake and Cholinergic Facilitation of Hippocampal Long-Term Potentiation by Acetylcholinesterase Inhibition. Neuroscience 2019; 404:39-47. [PMID: 30708046 DOI: 10.1016/j.neuroscience.2019.01.042] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2018] [Revised: 01/21/2019] [Accepted: 01/22/2019] [Indexed: 10/27/2022]
Abstract
Hippocampal cholinergic activity enhances long-term potentiation (LTP) of synaptic transmission in intrahippocampal circuits and regulates cognitive function. We recently demonstrated intracellular distribution of functional M1-muscarinic acetylcholine receptors (mAChRs) and neuronal uptake of acetylcholine (ACh) in the central nervous system. Here we examined whether endogenous ACh acts on intracellular M1-mAChRs following its uptake and causes cholinergic facilitation of hippocampal LTP. ACh esterase (AChE) activities and [3H]ACh uptake was measured in rat hippocampal segments. LTP of evoked field excitatory postsynaptic potentials at CA1 synapses was induced by high frequency stimulation in hippocampal slices. Pretreatment with diisopropylfluorophosphate (DFP) irreversibly inhibited AChE, augmented ACh uptake, and significantly enhanced the LTP. This cholinergic facilitation was inhibited by pirenzepine, a membrane-permeable M1 antagonist, while only the early stage of cholinergic facilitation was inhibited by a membrane-impermeable M1 antagonist, muscarinic toxin 7. Tetraethylammonium (TEA) inhibited ACh uptake in hippocampal segments and selectively suppressed late stage cholinergic facilitation without changing the early stage. In contrast, LTP in DFP-untreated slices was not affected by the muscarinic antagonists and TEA. Carbachol (CCh; an AChE-resistant muscarinic agonist) competed with ACh for its uptake and produced cholinergic facilitation of LTP in DFP-untreated slices. The late stage of CCh-induced facilitation was also selectively inhibited by TEA. Our results suggest that when AChE is inactivated by inhibitors, LTP in hippocampal slices is significantly enhanced by endogenous ACh and that cholinergic facilitation is caused by direct activation of cell-surface M1-mAChRs and subsequent activation of intracellular M1-mAChRs after ACh uptake.
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Affiliation(s)
- Takayoshi Masuoka
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, 1-1 Daigaku, Uchinada, Ishikawa, 920-0293, Japan.
| | - Junsuke Uwada
- Division of Cellular Signal Transduction, Department of Biochemistry, Asahikawa Medical University, 2-1-1-1, Midorigaoka-Higashi, Asahikawa, Hokkaido, 078-8510, Japan
| | - Makiko Kudo
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, 1-1 Daigaku, Uchinada, Ishikawa, 920-0293, Japan
| | - Hatsumi Yoshiki
- Division of Genomic Science and Microbiology, School of Medicine, University of Fukui, Eiheiji, Fukui 910-1193, Japan
| | - Yuka Yamashita
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, 1-1 Daigaku, Uchinada, Ishikawa, 920-0293, Japan
| | - Takanobu Taniguchi
- Division of Cellular Signal Transduction, Department of Biochemistry, Asahikawa Medical University, 2-1-1-1, Midorigaoka-Higashi, Asahikawa, Hokkaido, 078-8510, Japan
| | - Matomo Nishio
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, 1-1 Daigaku, Uchinada, Ishikawa, 920-0293, Japan
| | - Takaharu Ishibashi
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, 1-1 Daigaku, Uchinada, Ishikawa, 920-0293, Japan
| | - Ikunobu Muramatsu
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, 1-1 Daigaku, Uchinada, Ishikawa, 920-0293, Japan
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Muramatsu I, Uwada J, Masuoka T, Yoshiki H, Sada K, Lee KS, Nishio M, Ishibashi T, Taniguchi T. Regulation of synaptic acetylcholine concentrations by acetylcholine transport in rat striatal cholinergic transmission. J Neurochem 2017; 143:76-86. [PMID: 28700094 DOI: 10.1111/jnc.14127] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Revised: 06/17/2017] [Accepted: 06/29/2017] [Indexed: 11/29/2022]
Abstract
In addition to hydrolysis by acetylcholine esterase (AChE), acetylcholine (ACh) is also directly taken up into brain tissues. In this study, we examined whether the uptake of ACh is involved in the regulation of synaptic ACh concentrations. Superfusion experiments with rat striatal segments pre-incubated with [3 H]choline were performed using an ultra-mini superfusion vessel, which was developed to minimize superfusate retention within the vessel. Hemicholinium-3 (HC-3) at concentrations less than 1 μM, selectively inhibited the uptake of [3 H]choline by the high affinity-choline transporter 1 and had no effect on basal and electrically evoked [3 H]efflux in superfusion experiments. In contrast, HC-3 at higher concentrations, as well as tetraethylammonium (>10 μM), which inhibited the uptake of both [3 H]choline and [3 H]ACh, increased basal [3 H]overflow and potentiated electrically evoked [3 H]efflux. These effects of HC-3 and tetraethylammonium were also observed under conditions where tissue AChE was irreversibly inactivated by diisopropylfluorophosphate. Specifically, the potentiation of evoked [3 H]efflux was significantly higher in AChE-inactivated preparations and was attenuated by atropine. On the other hand, striatal segments pre-incubated with [3 H]ACh failed to increase [3 H]overflow in response to electrical stimulation. These results show that synaptic ACh concentrations are significantly regulated by the postsynaptic uptake of ACh, as well as by AChE hydrolysis and modulation of ACh release mediated through presynaptic muscarinic ACh receptors. In addition, these data suggest that the recycling of ACh-derived choline may be minor in cholinergic terminals. This study reveals a new mechanism of cholinergic transmission in the central nervous system.
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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
- Division of Cellular Signal Transduction, Department of Biochemistry, Asahikawa Medical University, Asahikawa, Hokkaido, Japan
| | - Takayoshi Masuoka
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, Uchinada, Ishikawa, Japan
| | - Hatsumi Yoshiki
- 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
| | - Kung-Shing Lee
- Division of Genomic Science and Microbiology, School of Medicine, University of Fukui, Eiheiji, Fukui, Japan.,Department of Surgery, Kaohsiung Medical University, Kaohsiung, Taiwan
| | - Matomo Nishio
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, Uchinada, Ishikawa, Japan
| | - Takaharu Ishibashi
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, Uchinada, Ishikawa, Japan
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Muramatsu I, Yoshiki H, Uwada J, Masuoka T, Sada K, Taniguchi T, Nishio M. Pharmacological evidence of specific acetylcholine transport in rat cerebral cortex and other brain regions. J Neurochem 2016; 139:566-575. [PMID: 27627023 DOI: 10.1111/jnc.13843] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Revised: 09/05/2016] [Accepted: 09/07/2016] [Indexed: 01/11/2023]
Abstract
Functional acetylcholine receptors (AChRs) were recently demonstrated to exist not only in the plasma membrane but also intracellularly in brain tissues. In order to activate intracellular AChRs, endogenous hydrophilic ACh must cross the plasma membrane. Here, we examined the pharmacological characteristics of this process, including whether it is mediated by active ACh uptake. When ACh esterase (AChE) was suppressed by diisopropylfluorophosphate, [3 H]ACh was effectively taken up into segments of rat cerebral cortex and other brain regions, in contrast to peripheral tissues such as liver and kidney. The uptake of [3 H]ACh in rat cerebral cortex was temperature-dependent, and the uptake capacity was comparable to that of [3 H]choline. However, [3 H]ACh uptake was inhibited by lower concentrations of ACh, carbachol, tetraethylammonium (TEA), compared with uptake of [3 H]choline. Uptake of [3 H]ACh was also inhibited by several organic cations, including choline, hemicholinium-3 (HC-3), quinidine, decynium 22, clonidine, diphenhydramine, but was little affected by some amino acids and biogenic amines, corticosterone, spermine, atropine, and tetrodotoxin. Unlike diisopropylfluorophosphate, several ACh esterase inhibitors, including drugs for Alzheimer's disease, such as donepezil, galantamine, and rivastigmine, also suppressed the uptake of [3 H]ACh, but not [3 H]choline. These results indicate that in the brain, ACh is specifically taken up through a unique transport system with different pharmacological properties from known organic cation transporters (OCTs), and suggest that this mechanism may be involved in intracellular cholinergic transmission in the brain.
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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
| | - Hatsumi Yoshiki
- Division of Genomic Science and Microbiology, School of Medicine, University of Fukui, Eiheiji, Fukui, Japan
| | - Junsuke Uwada
- Division of Cellular Signal Transduction, Department of Biochemistry, Asahikawa Medical University, Asahikawa, Hokkaido, Japan
| | - Takayoshi Masuoka
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, Uchinada, Ishikawa, Japan
| | - Kiyonao Sada
- Division of Genomic Science and Microbiology, School of Medicine, University of Fukui, Eiheiji, Fukui, Japan
| | - Takanobu Taniguchi
- Division of Cellular Signal Transduction, Department of Biochemistry, Asahikawa Medical University, Asahikawa, Hokkaido, Japan
| | - Matomo Nishio
- Department of Pharmacology, School of Medicine, Kanazawa Medical University, Uchinada, Ishikawa, Japan
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Carroll PT. Evidence to suggest that cytosolic acetylcholine in rat hippocampal nerve terminals is not directly transferred into synaptic vesicles for release. Brain Res 1996; 725:3-10. [PMID: 8828580 DOI: 10.1016/0006-8993(96)00078-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Rat hippocampal minces were loaded with [acetyl 1-14C]acetylcholine ([14C]ACh) in the presence of the "poorly penetrating" acetylcholinesterase (EC 3.1.1.7; AChE) inhibitor echothiophate and the effect of high K+ depolarization determined on the subcellular storage and release of [14C]ACh and its metabolites. Results indicated that high K+ did not augment the release of [14C]ACh. Rather, it increased the release of [14C]acetate while simultaneously reducing the level of [14C]ACh in the cytosolic (S3) fraction. When the identical experiment was performed with paraoxon, a "penetrating" AChE inhibitor, high K+ still did not increase the release of [14C]ACh. However, paraoxon prevented the K(+)-induced loss of [14C]ACh from the cytosolic fraction as well as the K(+)-induced gain of [14C]acetate in the release medium. When minces were loaded with [14C]ACh in the presence of echothiophate and subsequently subjected to high K+ depolarization in the absence or presence of vesamicol (AH5183; (-)-trans-2-[4-phenylpiperidino] cyclohexanol), a drug which blocks the refilling of synaptic vesicles with ACh, the amount of endogenous ACh released was reduced approximately 50%. Conversely, the amount of [14C]ACh released was not reduced at all. These results suggest that cytosolic ACh is not directly transported into synaptic vesicles for release when hippocampal nerve terminals are depolarized. Rather, its hydrolysis is accelerated in response to depolarization. A working hypothesis explaining the importance of the depolarization-induced breakdown of cytosolic ACh to central ACh metabolism is presented.
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Affiliation(s)
- P T Carroll
- Department of Pharmacology, Texas Tech University Health Sciences Center, Lubbock 79430, USA
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Evans SM, Kushner PD, Meyer EM. Actions of a monoclonal antibody Tor 23 on rat brain presynaptic cholinergic processes. Neurochem Res 1993; 18:339-44. [PMID: 8479603 DOI: 10.1007/bf00969093] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Tor 23 is a monoclonal antibody, generated against cholinergic terminals of the Torpedo californica, that has been found to bind to the extracellular surface of cholinergic neurons in a variety of tissues. This study shows that Tor 23 inhibits: 1) high affinity [3H]hemicholinium-3 binding to detergent-solubilized membranes prepared from rat neocortices; 2) high affinity [3H]choline uptake in rat neocortical and striatal P2 preparations; and 3) [3H]acetylcholine synthesis in isolated nerve terminals. Tor 23 does not appear to affect low affinity [3H]choline uptake or [3H]acetylcholine release. These results are consistent with the hypothesis that Tor 23 may bind to nerve terminal high affinity choline transporters in the rat brain.
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Affiliation(s)
- S M Evans
- Dept. of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville 32610-0267
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Umeda Y, Sumi T. Release of endogenous acetylcholine from rat brain slices with or without cholinesterase inhibition and its potentiation by hemicholinium-3. Neurosci Lett 1990; 118:276-8. [PMID: 2274284 DOI: 10.1016/0304-3940(90)90646-q] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The direct measurement of basal and high K(+)-stimulated release of endogenous acetylcholine from striatum and hippocampus slices was achieved without as well as with a cholinesterase inhibitor, physostigmine. Hemicholinium-3, opposite to its well-known activity as an inhibitor of endogenous acetylcholine release, significantly potentiated both the basal and stimulated release, in particular in the absence of physostigmine, suggesting an involvement of some unknown activity stimulating ACh release in hemicholinium-3.
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Affiliation(s)
- Y Umeda
- Division of Psychopharmacology, Psychiatric Research Institute of Tokyo, Japan
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Ballanyi K, Schlue WR. Electrophysiological characterization of a nicotinic acetylcholine receptor on leech neuropile glial cells. Glia 1989; 2:330-45. [PMID: 2530172 DOI: 10.1002/glia.440020506] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Ion-selective double-barrelled microelectrodes were used to measure the activities of intracellular K+, Na+, Cl-, and H+ (aiK, aiNa, aiCl, pHi) and membrane potential (Em) in neuropile glial cells as well as extracellular K+ activity (aeK) in the neuropile of the leech, Hirudo medicinalis, during bath application of carbachol. As measured with conventional single-barrelled microelectrodes, acetylcholine (ACh), nicotine, carbachol, tetramethylammonium (TMA), and choline elicited concentration-dependent (10(-6)-5 X 10(-3) M) transient membrane depolarizations of up to 60 mV amplitude whereas muscarine (10(-6)-10(-3) M) did not affect Em. alpha-Bungarotoxin (10(-7) M), decamethonium (10(-5) M), d-tubocurarine (5 X 10(-5) M), and strychnine (5 X 10(-5) M) blocked the carbachol depolarization by about 90%. Atropine (5 X 10(-5) M) blocked the response by about 75%, whereas hexamethonium was only effective at millimolar concentrations. Average baseline levels of aeK in the neuropile and of aiK, aiNa, and aiCl in the neuropile glial cells were about 3, 70, 10, and 7 mM, respectively. During the carbachol depolarization aeK and aiNa transiently increased, whereas aiK decreased. In contrast, a rise of aiK and a fall of aiNa were observed during glial depolarizations in solutions with elevated K+ concentration. aiCl increased during both the carbachol- and the K+-induced depolarization. During carbachol, pHi transiently fell by about 0.2 units from its average baseline level of 6.9, whereas an alkalinization of small amplitude was observed in high-K+ solutions. Bath-applied choline, TMA, and decamethonium rapidly accumulated in the neuropile glial cells as intracellularly monitored with double-barrelled microelectrodes filled with Corning K+ exchanger resin, which is highly selective for these agents. The results suggest that leech neuropile glial cells have a nicotinic ACh receptor coupled to a cation channel. It is hypothesized that this channel might also be permeable to choline, TMA, and decamethonium.
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Affiliation(s)
- K Ballanyi
- Institut für Zoologie, Universität Düsseldorf, Federal Republic of Germany
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Carroll PT, Badamchian M, Craig P, Lyness WH. Veratridine-induced breakdown of cytosolic acetylcholine in rat hippocampal minces: an intraterminal form of acetylcholinesterase or choline O-acetyltransferase? Brain Res 1986; 383:83-99. [PMID: 3768708 DOI: 10.1016/0006-8993(86)90010-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Rat hippocampal minces were loaded with N-methyl-[3H]acetylcholine ([3H]ACh) in the presence of the 'poorly penetrating' acetylcholinesterase (EC 3.1.1.7, AChE) inhibitor echothiophate and the effect of the depolarizing agent veratridine determined on the subcellular storage and release of [3H]ACh and [3H]choline. Results indicated that veratridine stimulated the release of [3H]ACh from a crude vesicular fraction (P3) by a Ca2+-dependent process, while simultaneously accelerating the breakdown of cytosolic (S3) [3H]ACh. A portion of the [3H]choline derived from the hydrolyzed S3 [3H]ACh was donated to the P3 fraction for [3H]ACh formation and release. When the identical experiment was done using hippocampal minces from septal lesioned rats, veratridine did not stimulate either the Ca2+-dependent release of [3H]ACh or the hydrolysis of cytosolic [3H]ACh. Incubation of control hippocampal minces with paraoxon, an AChE inhibitor which can penetrate cholinergic nerve terminals more rapidly than echothiophate, prevented veratridine from stimulating the Ca2+-dependent release of [3H]ACh from the P3 fraction. Instead, it then stimulated the Ca2+-independent release of [3H]ACh from the S3 fraction. When minces were incubated with the choline O-acetyltransferase (EC 2.3.1.6, ChAT) inhibitor 4-(1-naphthyl)vinyl pyridine (NVP), veratridine was no longer able to stimulate the Ca2+-dependent release of labelled ACh either. Instead, veratridine stimulated the Ca2+-independent release of labelled ACh from the S3 fraction. NVP also abolished the veratridine-induced, Ca2+-dependent release of total ACh. Both paraoxon and NVP inhibited the reversible reaction of ionically bound ChAT prepared from rat brain when tested in vitro, yet paraoxon was much less potent than NVP, and was unable to inhibit this reaction at the low concentration which prevented the veratridine induced breakdown of S3 [3H]ACh during mince incubation. Veratridine depolarization of hippocampal minces stimulated the activity of a membrane-bound fraction of ChAT associated with the P3 fraction, but this fraction of ChAT did not become more sensitive to inhibition by paraoxon during tissue incubation. Veratridine depolarization of minces also increased the activity of membrane-bound AChE, but this enzyme was not inhibited by the low NVP concentration which prevented the veratridine-induced breakdown of S3 [3H]ACh. The veratridine-induced increase in membrane-bound ChAT activity was dependent on the presence of extracellular Ca2+ in the incubation medium.(ABSTRACT TRUNCATED AT 400 WORDS)
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Nelson SH, Benishin CG, Carroll PT. Accumulation and metabolism of choline and homocholine by mouse brain subcellular fractions. Biochem Pharmacol 1980; 29:1949-57. [PMID: 7397001 DOI: 10.1016/0006-2952(80)90109-4] [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: 01/25/2023]
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Grewaal DS, Quastel JH. Uptake and release of exogenous [1-14C]acetylcholine by brain cortex slices from the rat. J Neurochem 1979; 32:1235-48. [PMID: 430083 DOI: 10.1111/j.1471-4159.1979.tb11051.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Carrol PT, Nelson SH. Cholinergic Vesicles: Ability to Empty and Refill Independently of Cytoplasmic Acetylcholine. Science 1978; 199:85-6. [PMID: 17569492 DOI: 10.1126/science.199.4324.85] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Incubation of minced mouse-forebrain tissues in lithium Krebs solution reduces the acetylcholine content of the vesicular fraction 70 percent without altering that of the cytoplasmic fraction. Depleted vesicular-bound acetylcholine can be restored with newly synthesized acetylcholine (formed from extracellular choline) independently of the cytoplasmic pool. Depletion of vesicular-bound acetylcholine does not facilitate the movement of preformed extracellular acetylcholine into vesicles.
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Affiliation(s)
- P T Carrol
- Department of Pharmacology and Toxicology, University of Rhode Island, Kingston, RI 02881, USA
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Storm-Mathisen J. Localization of transmitter candidates in the brain: the hippocampal formation as a model. Prog Neurobiol 1977; 8:119-81. [PMID: 14356 DOI: 10.1016/0301-0082(77)90013-2] [Citation(s) in RCA: 352] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Borison HL. Central nervous respiratory depressants--control-systems approach to respiratory depression. PHARMACOLOGY & THERAPEUTICS. PART B: GENERAL & SYSTEMATIC PHARMACOLOGY 1977; 3:211-26. [PMID: 201942 DOI: 10.1016/0306-039x(77)90033-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Collier B, Katz HS. Studies upon the mechanism by which acetylcholine releases surplus acetylcholine in a sympathetic ganglion. Br J Pharmacol 1975; 55:189-97. [PMID: 1201377 PMCID: PMC1666862 DOI: 10.1111/j.1476-5381.1975.tb07628.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: 12/26/2022] Open
Abstract
1. Acetylcholine (ACh) releases surplus ACh from the superior cervical ganglion of the cat and the experiments described in this paper tested whether this results from exchange of endogenous ACh with exogenous ACh; the experiments also attempted to characterize pharmacologically the mechanism of this action of ACh. 2. The surplus ACh in the ganglion was radioactively labelled by perfusion of the ganglion with [3H]-choline-Krebs solution containing diisopropylphosphofluoridate, and the release of surplus [3H]-ACh by [14C]-ACh injected close arterially to the ganglion measured. The amount of [3H]-ACh released by [14C]-ACh was 33 +/- 5 times greater than was the amount of [14C]-ACh accumulated by ganglia. The amount of exogenous ACh accumulated by ganglia that had first formed surplus ACh was not different from exogenous ACh accumulation by ganglia that had not formed surplus ACh. Thus, it is concluded that surplus ACh release by ACh is not the result of ACh exchange. 3. In other experiments, surplus [3H]-ACh was accumulated in ganglia exposed to physostigmine. Nicotine, pilocarpine or ACh released surplus ACh; the effect of both nicotine and ACh was blocked by hexamethonium; atropine blocked the effect of ACh but not that of nicotine. It is concluded that both nicotinic and muscarinic receptors can be involved in the release of surplus ACh by cholinomimetic agonists.
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Abstract
1. The recapture and re-use of choline formed by the hydrolysis of released acetylcholine (ACh) was studied in the superior cervical ganglion of the cat using radioactive tracer techniques. The ganglion's ACh store was labelled by perfusion, during preganglionic nerve stimulation, with Krebs solution containing [(3)H]choline.2. Preganglionic stimulation (5 Hz for 20 min) of ganglia containing [(3)H]ACh released similar amounts of radioactivity when perfusion was with neostigmine-choline-Krebs or with hemicholinium-Krebs. This indicated that neostigmine does not increase transmitter release.3. The amount of radioactivity collected from stimulated ganglia during perfusion with choline-Krebs was 39% of the amount of radioactivity collected during perfusion with medium containing neostigmine or hemi-cholinium. This difference in release was almost (85%) accounted for at the end of the experiment by extra radioactive ACh in the ganglia perfused with choline-Krebs. It is concluded that during preganglionic nerve stimulation approximately 50-60% of endogenously produced choline is recaptured for ACh synthesis; thus, during activity preganglionic nerve terminals appear selectively to accumulate choline.4. However, chronically decentralized ganglia accumulated as much choline as did acutely decentralized ganglia, and this was interpreted as indicating that at rest preganglionic nerve terminals do not selectively accumulate choline.5. Increased exogenous choline concentration increased the amount of radioactivity collected during nerve stimulation in the absence, but not the presence, of an anticholinesterase agent. The spontaneous efflux of radioactivity was little affected by changes in external choline levels. It is concluded that exogenous choline and choline made available from released transmitter compete for uptake into nerve terminals.
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White GL, Schellhase HU, Hawthorne JN. Phosphoinositide metabolism in rat superior cervical ganglion, vagus and phrenic nerve: effects of electrical stimulation and various blocking agents. J Neurochem 1974; 22:149-58. [PMID: 4362075 DOI: 10.1111/j.1471-4159.1974.tb12191.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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