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Zholos AV, Melnyk MI, Dryn DO. Molecular mechanisms of cholinergic neurotransmission in visceral smooth muscles with a focus on receptor-operated TRPC4 channel and impairment of gastrointestinal motility by general anaesthetics and anxiolytics. Neuropharmacology 2024; 242:109776. [PMID: 37913983 DOI: 10.1016/j.neuropharm.2023.109776] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Revised: 10/13/2023] [Accepted: 10/23/2023] [Indexed: 11/03/2023]
Abstract
Acetylcholine is the primary excitatory neurotransmitter in visceral smooth muscles, wherein it binds to and activates two muscarinic receptors subtypes, M2 and M3, thus causing smooth muscle excitation and contraction. The first part of this review focuses on the types of cells involved in cholinergic neurotransmission and on the molecular mechanisms underlying acetylcholine-induced membrane depolarisation, which is the central event of excitation-contraction coupling causing Ca2+ entry via L-type Ca2+ channels and smooth muscle contraction. Studies of the muscarinic cation current in intestinal myocytes (mICAT) revealed its main molecular counterpart, receptor-operated TRPC4 channel, which is activated in synergy by both M2 and M3 receptors. M3 receptors activation is of permissive nature, while activation of M2 receptors via Gi/o proteins that are coupled to them plays a direct role in TRPC4 opening. Our understanding of signalling pathways underlying mICAT generation has vastly expanded in recent years through studies of TRPC4 gating in native cells and its regulation in heterologous cells. Recent studies using muscarinic receptor knockout have established that at low agonist concentration activation of both M2 receptor and the M2/M3 receptor complex elicits smooth muscle contraction, while at high agonist concentration M3 receptor function becomes dominant. Based on this knowledge, in the second part of this review we discuss the cellular and molecular mechanisms underlying the numerous anticholinergic effects on neuroactive drugs, in particular general anaesthetics and anxiolytics, which can significantly impair gastrointestinal motility. This article is part of the Special Issue on "Ukrainian Neuroscience".
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Affiliation(s)
- Alexander V Zholos
- Educational and Scientific Centre "Institute of Biology and Medicine", Taras Shevchenko National University of Kyiv, Kyiv, Ukraine.
| | - Mariia I Melnyk
- Educational and Scientific Centre "Institute of Biology and Medicine", Taras Shevchenko National University of Kyiv, Kyiv, Ukraine; A.A. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine
| | - Dariia O Dryn
- A.A. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine
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Dryn DO, Melnyk MI, Bon RS, Beech DJ, Zholos AV. Pico145 inhibits TRPC4-mediated mI CAT and postprandial small intestinal motility. Biomed Pharmacother 2023; 168:115672. [PMID: 37857250 DOI: 10.1016/j.biopha.2023.115672] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Revised: 10/04/2023] [Accepted: 10/06/2023] [Indexed: 10/21/2023] Open
Abstract
In intestinal smooth muscle cells, receptor-operated TRPC4 are responsible for the majority of muscarinic receptor cation current (mICAT), which initiates cholinergic excitation-contraction coupling. Our aim was to examine the effects of the TRPC4 inhibitor Pico145 on mICAT and Ca2+ signalling in mouse ileal myocytes, and on intestinal motility. Ileal myocytes freshly isolated from two month-old male BALB/c mice were used for patch-clamp recordings of whole-cell currents and for intracellular Ca2+ imaging using Fura-2. Functional assessment of Pico145's effects was carried out by standard in vitro tensiometry, ex vivo video recordings and in vivo postprandial intestinal transit measurements using carmine red. Carbachol (50 µM)-induced mICAT was strongly inhibited by Pico145 starting from 1 pM. The IC50 value for the inhibitory effect of Pico145 on this current evoked by intracellularly applied GTPγS (200 µM), and thus lacking desensitisation, was found to be 3.1 pM, while carbachol-induced intracellular Ca2+ rises were inhibited with IC50 of 2.7 pM. In contrast, the current activated by direct TRPC4 agonist (-)-englerin A was less sensitive to the action of Pico145 that caused only ∼43 % current inhibition at 100 pM. The inhibitory effect developed rather slowly and it was potentiated by membrane depolarisation. In functional assays, Pico145 produced concentration-dependent suppression of both spontaneous and carbachol-evoked intestinal smooth muscle contractions and delayed postprandial intestinal transit. Thus, Pico145 is a potent GI-active small-molecule which completely inhibits mICAT at picomolar concentrations and which is as effective as trpc4 gene deficiency in in vivo intestinal motility tests.
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Affiliation(s)
- Dariia O Dryn
- A.A. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, 4 Bogomoletz Str., Kyiv 01024, Ukraine
| | - Mariia I Melnyk
- A.A. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, 4 Bogomoletz Str., Kyiv 01024, Ukraine; Educational and Scientific Centre "Institute of Biology and Medicine", Taras Shevchenko National University of Kyiv, 64 Volodymyrska Str., Kyiv 01601, Ukraine
| | - Robin S Bon
- Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - David J Beech
- Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Alexander V Zholos
- Educational and Scientific Centre "Institute of Biology and Medicine", Taras Shevchenko National University of Kyiv, 64 Volodymyrska Str., Kyiv 01601, Ukraine.
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Zholos AV, Dryn DO, Melnyk MI. General anaesthesia-related complications of gut motility with a focus on cholinergic mechanisms, TRP channels and visceral pain. Front Physiol 2023; 14:1174655. [PMID: 37275228 PMCID: PMC10232893 DOI: 10.3389/fphys.2023.1174655] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Accepted: 05/09/2023] [Indexed: 06/07/2023] Open
Abstract
General anesthesia produces multiple side effects. Notably, it temporarily impairs gastrointestinal motility following surgery and causes the so-called postoperative ileus (POI), a multifactorial and complex condition that develops secondary to neuromuscular failure and mainly affects the small intestine. There are currently limited medication options for POI, reflecting a lack of comprehensive understanding of the mechanisms involved in this complex condition. Notably, although acetylcholine is one of the major neurotransmitters initiating excitation-contraction coupling in the gut, cholinergic stimulation by prokinetic drugs is not very efficient in case of POI. Acetylcholine when released from excitatory motoneurones of the enteric nervous system binds to and activates M2 and M3 types of muscarinic receptors in smooth muscle myocytes. Downstream of these G protein-coupled receptors, muscarinic cation TRPC4 channels act as the major focal point of receptor-mediated signal integration, causing membrane depolarisation accompanied by action potential discharge and calcium influx via L-type Ca2+ channels for myocyte contraction. We have recently found that both inhalation (isoflurane) and intravenous (ketamine) anesthetics significantly inhibit this muscarinic cation current (termed mI CAT) in ileal myocytes, even when G proteins are activated directly by intracellular GTPγS, i.e., bypassing muscarinic receptors. Here we aim to summarize Transient Receptor Potential channels and calcium signalling-related aspects of the cholinergic mechanisms in the gut and visceral pain, discuss exactly how these may be negatively impacted by general anaesthetics, while proposing the receptor-operated TRPC4 channel as a novel molecular target for the treatment of POI.
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Affiliation(s)
- Alexander V. Zholos
- ESC “Institute of Biology and Medicine”, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
| | - Dariia O. Dryn
- O.O. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine
| | - Mariia I. Melnyk
- ESC “Institute of Biology and Medicine”, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
- O.O. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine
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Al Kury LT, Papandreou D, Hurmach VV, Dryn DO, Melnyk MI, Platonov MO, Prylutskyy YI, Ritter U, Scharff P, Zholos AV. Single-Walled Carbon Nanotubes Inhibit TRPC4-Mediated Muscarinic Cation Current in Mouse Ileal Myocytes. NANOMATERIALS 2021; 11:nano11123410. [PMID: 34947764 PMCID: PMC8703819 DOI: 10.3390/nano11123410] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 12/10/2021] [Accepted: 12/13/2021] [Indexed: 12/02/2022]
Abstract
Single-walled carbon nanotubes (SWCNTs) are characterized by a combination of rather unique physical and chemical properties, which makes them interesting biocompatible nanostructured materials for various applications, including in the biomedical field. SWCNTs are not inert carriers of drug molecules, as they may interact with various biological macromolecules, including ion channels. To investigate the mechanisms of the inhibitory effects of SWCNTs on the muscarinic receptor cation current (mICAT), induced by intracellular GTPγs (200 μM), in isolated mouse ileal myocytes, we have used the patch-clamp method in the whole-cell configuration. Here, we use molecular docking/molecular dynamics simulations and direct patch-clamp recordings of whole-cell currents to show that SWCNTs, purified and functionalized by carboxylation in water suspension containing single SWCNTs with a diameter of 0.5–1.5 nm, can inhibit mICAT, which is mainly carried by TRPC4 cation channels in ileal smooth muscle cells, and is the main regulator of cholinergic excitation–contraction coupling in the small intestinal tract. This inhibition was voltage-independent and associated with a shortening of the mean open time of the channel. These results suggest that SWCNTs cause a direct blockage of the TRPC4 channel and may represent a novel class of TRPC4 modulators.
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Affiliation(s)
- Lina T. Al Kury
- College of Natural and Health Sciences, Zayed University, Abu Dhabi 144534, United Arab Emirates; (L.T.A.K.); (D.P.)
| | - Dimitrios Papandreou
- College of Natural and Health Sciences, Zayed University, Abu Dhabi 144534, United Arab Emirates; (L.T.A.K.); (D.P.)
| | - Vasyl V. Hurmach
- ESC “Institute of Biology and Medicine”, Taras Shevchenko National University of Kyiv, 64 Volodymyrska Str., 01601 Kyiv, Ukraine; (V.V.H.); (D.O.D.); (M.I.M.); (Y.I.P.)
| | - Dariia O. Dryn
- ESC “Institute of Biology and Medicine”, Taras Shevchenko National University of Kyiv, 64 Volodymyrska Str., 01601 Kyiv, Ukraine; (V.V.H.); (D.O.D.); (M.I.M.); (Y.I.P.)
- O.O. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, 4 Bogomoletz Str., 01024 Kyiv, Ukraine
- Institute of Pharmacology and Toxicology, National Academy of Medical Sciences of Ukraine, 14 Anton Tsedik Str., 03057 Kyiv, Ukraine
| | - Mariia I. Melnyk
- ESC “Institute of Biology and Medicine”, Taras Shevchenko National University of Kyiv, 64 Volodymyrska Str., 01601 Kyiv, Ukraine; (V.V.H.); (D.O.D.); (M.I.M.); (Y.I.P.)
- O.O. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, 4 Bogomoletz Str., 01024 Kyiv, Ukraine
- Institute of Pharmacology and Toxicology, National Academy of Medical Sciences of Ukraine, 14 Anton Tsedik Str., 03057 Kyiv, Ukraine
| | - Maxim O. Platonov
- Institute of Molecular Biology and Genetics, National Academy of Sciences of Ukraine, 150 Zabolotnogo Str., 03143 Kyiv, Ukraine;
| | - Yuriy I. Prylutskyy
- ESC “Institute of Biology and Medicine”, Taras Shevchenko National University of Kyiv, 64 Volodymyrska Str., 01601 Kyiv, Ukraine; (V.V.H.); (D.O.D.); (M.I.M.); (Y.I.P.)
| | - Uwe Ritter
- Institute of Chemistry and Biotechnology, Technical University of Ilmenau, 25 Weimarer Str., 98693 Ilmenau, Germany; (U.R.); (P.S.)
| | - Peter Scharff
- Institute of Chemistry and Biotechnology, Technical University of Ilmenau, 25 Weimarer Str., 98693 Ilmenau, Germany; (U.R.); (P.S.)
| | - Alexander V. Zholos
- ESC “Institute of Biology and Medicine”, Taras Shevchenko National University of Kyiv, 64 Volodymyrska Str., 01601 Kyiv, Ukraine; (V.V.H.); (D.O.D.); (M.I.M.); (Y.I.P.)
- Correspondence: ; Tel.: +380-44-4312-0403
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Tanahashi Y, Komori S, Matsuyama H, Kitazawa T, Unno T. Functions of Muscarinic Receptor Subtypes in Gastrointestinal Smooth Muscle: A Review of Studies with Receptor-Knockout Mice. Int J Mol Sci 2021; 22:E926. [PMID: 33477687 PMCID: PMC7831928 DOI: 10.3390/ijms22020926] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2020] [Revised: 01/12/2021] [Accepted: 01/14/2021] [Indexed: 01/25/2023] Open
Abstract
Parasympathetic signalling via muscarinic acetylcholine receptors (mAChRs) regulates gastrointestinal smooth muscle function. In most instances, the mAChR population in smooth muscle consists mainly of M2 and M3 subtypes in a roughly 80% to 20% mixture. Stimulation of these mAChRs triggers a complex array of biochemical and electrical events in the cell via associated G proteins, leading to smooth muscle contraction and facilitating gastrointestinal motility. Major signalling events induced by mAChRs include adenylyl cyclase inhibition, phosphoinositide hydrolysis, intracellular Ca2+ mobilisation, myofilament Ca2+ sensitisation, generation of non-selective cationic and chloride currents, K+ current modulation, inhibition or potentiation of voltage-dependent Ca2+ currents and membrane depolarisation. A lack of ligands with a high degree of receptor subtype selectivity and the frequent contribution of multiple receptor subtypes to responses in the same cell type have hampered studies on the signal transduction mechanisms and functions of individual mAChR subtypes. Therefore, novel strategies such as genetic manipulation are required to elucidate both the contributions of specific AChR subtypes to smooth muscle function and the underlying molecular mechanisms. In this article, we review recent studies on muscarinic function in gastrointestinal smooth muscle using mAChR subtype-knockout mice.
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Affiliation(s)
- Yasuyuki Tanahashi
- Department of Advanced Life Sciences, Faculty of Life Sciences, Kyoto Sangyo University, Kyoto 603-8555, Japan;
| | - Seiichi Komori
- Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Sciences, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan; (S.K.); (H.M.)
| | - Hayato Matsuyama
- Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Sciences, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan; (S.K.); (H.M.)
| | - Takio Kitazawa
- Department of Veterinary Science, Rakuno Gakuen University, Ebetsu, Hokkaido 069-8501, Japan;
| | - Toshihiro Unno
- Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Sciences, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan; (S.K.); (H.M.)
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Melnyk MI, Dryn DO, Al Kury LT, Dziuba DO, Zholos AV. Suppression of mI CAT in Mouse Small Intestinal Myocytes by General Anaesthetic Ketamine and its Recovery by TRPC4 Agonist (-)-englerin A. Front Pharmacol 2021; 11:594882. [PMID: 33390980 PMCID: PMC7775583 DOI: 10.3389/fphar.2020.594882] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 11/02/2020] [Indexed: 11/19/2022] Open
Abstract
A better understanding of the negative impact of general anesthetics on gastrointestinal motility requires thorough knowledge of their molecular targets. In this respect the muscarinic cationic current (mICAT carried mainly via TRPC4 channels) that initiates cholinergic excitation-contraction coupling in the gut is of special interest. Here we aimed to characterize the effects of one of the most commonly used “dissociative anesthetics”, ketamine, on mICAT. Patch-clamp and tensiometry techniques were used to investigate the mechanisms of the inhibitory effects of ketamine on mICAT in single mouse ileal myocytes, as well as on intestinal motility. Ketamine (100 µM) strongly inhibited both carbachol- and GTPγS-induced mICAT. The inhibition was slow (time constant of about 1 min) and practically irreversible. It was associated with altered voltage dependence and kinetics of mICAT. In functional tests, ketamine suppressed both spontaneous and carbachol-induced contractions of small intestine. Importantly, inhibited by ketamine mICAT could be restored by direct TRPC4 agonist (-)-englerin A. We identified mICAT as a novel target for ketamine. Signal transduction leading to TRPC4 channel opening is disrupted by ketamine mainly downstream of muscarinic receptor activation, but does not involve TRPC4 per se. Direct TRPC4 agonists may be used for the correction of gastrointestinal disorders provoked by general anesthesia.
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Affiliation(s)
- Mariia I Melnyk
- A.A. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine.,Institute of Pharmacology and Toxicology, National Academy of Medical Science of Ukraine, Kyiv, Ukraine.,ESC "Institute of Biology and Medicine", Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
| | - Dariia O Dryn
- A.A. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine.,Institute of Pharmacology and Toxicology, National Academy of Medical Science of Ukraine, Kyiv, Ukraine.,ESC "Institute of Biology and Medicine", Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
| | - Lina T Al Kury
- Department of Health Sciences, Zayed University, Abu Dhabi, United Arab Emirates
| | - Dmytro O Dziuba
- Shupyk National Medical Academy of Postgraduate Education, Kyiv, Ukraine
| | - Alexander V Zholos
- ESC "Institute of Biology and Medicine", Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
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Tanahashi Y, Katsurada T, Inasaki N, Uchiyama M, Sakamoto T, Yamamoto M, Matsuyama H, Komori S, Unno T. Further characterization of the synergistic activation mechanism of cationic channels by M 2 and M 3 muscarinic receptors in mouse intestinal smooth muscle cells. Am J Physiol Cell Physiol 2019; 318:C514-C523. [PMID: 31875697 DOI: 10.1152/ajpcell.00277.2019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
In mouse ileal myocytes, muscarinic receptor-mediated cationic current (mIcat) occurs mainly through synergism of M2 and M3 subtypes involving Gi/o-type GTP-binding proteins and phospholipase C (PLC). We have further studied the M2/M3 synergistic pathway. Carbachol-induced mIcat was markedly depressed by YM-254890, a Gq/11 protein inhibitor. However, the mIcat was unaffected by heparin, calphostin C, or chelerythrine, suggesting that mIcat activation does not involve signaling molecules downstream of phosphatidylinositol 4,5-bisphosphate (PIP2) breakdown. M2-knockout (KO) mice displayed a reduced mIcat (~10% of wild-type mIcat) because of the lack of M2-Gi/o signaling. The impaired mIcat was insensitive to neuropeptide Y possessing a Gi/o-stimulating activity. M3-KO mice also displayed a reduced mIcat (~6% of wild-type mIcat) because of the lack of M3-Gq/11 signaling, and the mIcat was insensitive to prostaglandin F2α possessing a Gq/11-stimulating activity. These results suggest the importance of Gq/11/PLC-hydrolyzed PIP2 breakdown itself in mIcat activation and also support the idea that the M2/M3 synergistic pathway represents a signaling complex consisting of M2-Gi/o and M3-Gq/11-PLC systems in which both G proteins are special for this pathway but not general in receptor coupling.
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Affiliation(s)
- Yasuyuki Tanahashi
- Department of Animal Medical Sciences, Faculty of Life Sciences, Kyoto Sangyo University, Kyoto, Japan
| | - Taisuke Katsurada
- Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Science, Gifu University, Gifu, Japan
| | - Noriko Inasaki
- Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Science, Gifu University, Gifu, Japan
| | - Mai Uchiyama
- Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Science, Gifu University, Gifu, Japan
| | - Takashi Sakamoto
- Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Science, Gifu University, Gifu, Japan
| | - Masayuki Yamamoto
- Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Science, Gifu University, Gifu, Japan
| | - Hayato Matsuyama
- Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Science, Gifu University, Gifu, Japan
| | - Seiichi Komori
- Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Science, Gifu University, Gifu, Japan
| | - Toshihiro Unno
- Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Science, Gifu University, Gifu, Japan
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C 60 fullerenes disrupt cellular signalling leading to TRPC4 and TRPC6 channels opening by the activation of muscarinic receptors and G-proteins in small intestinal smooth muscles. Cell Signal 2017; 43:40-46. [PMID: 29242169 DOI: 10.1016/j.cellsig.2017.12.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 11/27/2017] [Accepted: 12/10/2017] [Indexed: 01/03/2023]
Abstract
The effect of water-soluble pristine C60 fullerene nanoparticles (C60NPs) on receptor-operated cation channels formed by TRPC4/C6 proteins in ileal smooth muscle cells was investigated for the first time. Activation of these channels subsequent to acetylcholine binding to the expressed in these cells M2 and M3 muscarinic receptors represents the key event in the parasympathetic control of gastrointestinal smooth muscle motility and cholinergic excitation-contraction coupling. Experiments were performed on single collagenase-dispersed mouse ileal myocytes using patch-clamp techniques with symmetrical 125mM Cs+ solutions and [Ca2+]i 'clamped' at 100nM in order to isolate the muscarinic cation current (mICAT). The current was induced by intracellular infusion of 200μM GTPγS, which activates G-proteins directly, i.e. bypassing the muscarinic receptors. C60NPs applied at 10-6M at peak response to activation of G-proteins caused mICAT inhibition by 47.0±3.5% (n=9). The inhibition developed rather slowly, with the time constant of 119±16s, was voltage-independent and irreversible. Thus, C60NPs are unlikely to cause any direct block of TRPC4/C6 channels; rather, they may accumulate in the membrane and disrupt G-protein signalling leading to mICAT generation. C60NPs may represent a novel class of biocompatible molecules for the treatment of disorders associated with enhanced gastrointestinal motility.
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Abstract
TRPC4 proteins comprise six transmembrane domains, a putative pore-forming region, and an intracellularly located amino- and carboxy-terminus. Among eleven splice variants identified so far, TRPC4α and TRPC4β are the most abundantly expressed and functionally characterized. TRPC4 is expressed in various organs and cell types including the soma and dendrites of numerous types of neurons; the cardiovascular system including endothelial, smooth muscle, and cardiac cells; myometrial and skeletal muscle cells; kidney; and immune cells such as mast cells. Both recombinant and native TRPC4-containing channels differ tremendously in their permeability and other biophysical properties, pharmacological modulation, and mode of activation depending on the cellular environment. They vary from inwardly rectifying store-operated channels with a high Ca(2+) selectivity to non-store-operated channels predominantly carrying Na(+) and activated by Gαq- and/or Gαi-coupled receptors with a complex U-shaped current-voltage relationship. Thus, individual TRPC4-containing channels contribute to agonist-induced Ca(2+) entry directly or indirectly via depolarization and activation of voltage-gated Ca(2+) channels. The differences in channel properties may arise from variations in the composition of the channel complexes, in the specific regulatory pathways in the corresponding cell system, and/or in the expression pattern of interaction partners which comprise other TRPC proteins to form heteromultimeric channels. Additional interaction partners of TRPC4 that can mediate the activity of TRPC4-containing channels include (1) scaffolding proteins (e.g., NHERF) that may mediate interactions with signaling molecules in or in close vicinity to the plasma membrane such as Gα proteins or phospholipase C and with the cytoskeleton, (2) proteins in specific membrane microdomains (e.g., caveolin-1), or (3) proteins on cellular organelles (e.g., Stim1). The diversity of TRPC4-containing channels hampers the development of specific agonists or antagonists, but recently, ML204 was identified as a blocker of both recombinant and endogenous TRPC4-containing channels with an IC50 in the lower micromolar range that lacks activity on most voltage-gated channels and other TRPs except TRPC5 and TRPC3. Lanthanides are specific activators of heterologously expressed TRPC4- and TRPC5-containing channels but can block individual native TRPC4-containing channels. The biological relevance of TRPC4-containing channels was demonstrated by knockdown of TRPC4 expression in numerous native systems including gene expression, cell differentiation and proliferation, formation of myotubes, and axonal regeneration. Studies of TRPC4 single and TRPC compound knockout mice uncovered their role for the regulation of vascular tone, endothelial permeability, gastrointestinal contractility and motility, neurotransmitter release, and social exploratory behavior as well as for excitotoxicity and epileptogenesis. Recently, a single-nucleotide polymorphism (SNP) in the Trpc4 gene was associated with a reduced risk for experience of myocardial infarction.
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Affiliation(s)
- Marc Freichel
- Pharmakologisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 366, 69120, Heidelberg, Germany,
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Koh SD, Rhee PL. Ionic Conductance(s) in Response to Post-junctional Potentials. J Neurogastroenterol Motil 2013; 19:426-32. [PMID: 24199003 PMCID: PMC3816177 DOI: 10.5056/jnm.2013.19.4.426] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Revised: 08/28/2013] [Accepted: 08/30/2013] [Indexed: 01/29/2023] Open
Abstract
The gastrointestinal motility is regulated by extrinsic and intrinsic neural regulation. Intrinsic neural pathways are controlled by sensory input, inter-neuronal relay and motor output. Enteric motor neurons release many transmitters which affect post-junctional responses. Post-junctional responses can be excitatory and inhibitory depending on neurotransmitters. Excitatory neurotransmitters induce depolarization and contraction. In contrast, inhibitory neurotransmitters hyperpolarize and relaxe the gastrointestinal smooth muscle. Smooth muscle syncytium is composed of smooth muscle cells, interstitial cells of Cajal and platelet-derived growth factor receptor α-positive (PDGFRα(+)) cells (SIP syncytium). Specific expression of receptors and ion channels in these cells can be affected by neurotransmitters. In recent years, molecular reporter expression techniques are able to study the properties of ion channels and receptors in isolated specialized cells. In this review, we will discuss the mechanisms of ion channels to interpret the post-junctional responses in the gastrointestinal smooth muscles.
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Affiliation(s)
- Sang Don Koh
- Department of Physiology and Cell Biology, University of Nevada, School of Medicine, Reno, NV, USA
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11
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Mitchelson FJ. The pharmacology of McN-A-343. Pharmacol Ther 2012; 135:216-45. [DOI: 10.1016/j.pharmthera.2012.05.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Accepted: 05/07/2012] [Indexed: 01/01/2023]
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Abstract
The physiological role of muscarinic receptors is highly complex and, although not completely understood, has become clearer over the last decade. Recent pharmacological evidence with novel compounds, together with data from transgenic mice, suggests that all five subtypes have defined functions in the nervous system as well as mediating the non neuronal, hormonal actions of acetylcholine. Numerous novel agonists, allosteric regulators, and antagonists have now been identified with authentic subtype specificity in vitro and in vivo. These compounds provide additional pharmacological opportunities for selective subtype modulation as well as a new generation of muscarinic receptor-based therapeutics.
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Affiliation(s)
- Richard M Eglen
- Corning Life Sciences, 900 Chelmsford St., MA 01851, Lowell, USA.
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13
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Tsvilovskyy VV, Zholos AV, Aberle T, Philipp SE, Dietrich A, Zhu MX, Birnbaumer L, Freichel M, Flockerzi V. Deletion of TRPC4 and TRPC6 in mice impairs smooth muscle contraction and intestinal motility in vivo. Gastroenterology 2009; 137:1415-24. [PMID: 19549525 PMCID: PMC2757464 DOI: 10.1053/j.gastro.2009.06.046] [Citation(s) in RCA: 138] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2008] [Revised: 05/20/2009] [Accepted: 06/18/2009] [Indexed: 12/02/2022]
Abstract
BACKGROUND & AIMS Downstream effects of muscarinic receptor stimulation in intestinal smooth muscle include contraction and intestinal transit. We thought to determine whether classic transient receptor potential (TRPC) channels integrate the intracellular signaling cascades evoked by the stimulated receptors and thereby contribute to the control of the membrane potential, Ca-influx, and cell responses. METHODS We created trpc4-, trpc6-, and trpc4/trpc6-gene-deficient mice and analyzed them for intestinal smooth muscle function in vitro and in vivo. RESULTS In intestinal smooth muscle cells TRPC4 forms a 55 pS cation channel and underlies more than 80% of the muscarinic receptor-induced cation current (mI(CAT)). The residual mI(CAT) depends on the expression of TRPC6, indicating that TRPC6 and TRPC4 determine mI(CAT) channel activity independent of other channel subunits. In TRPC4-deficient ileal myocytes the carbachol-induced membrane depolarizations are diminished greatly and the atropine-sensitive contraction elicited by acetylcholine release from excitatory motor neurons is reduced greatly. Additional deletion of TRPC6 aggravates these effects. Intestinal transit is slowed down in mice lacking TRPC4 and TRPC6. CONCLUSIONS In intestinal smooth muscle cells TRPC4 and TRPC6 channels are gated by muscarinic receptors and are responsible for mI(CAT). They couple muscarinic receptors to depolarization of intestinal smooth muscle cells and voltage-activated Ca(2+)-influx and contraction, and thereby accelerate small intestinal motility in vivo.
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Affiliation(s)
- Volodymyr V. Tsvilovskyy
- Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg, Germany
| | - Alexander V. Zholos
- Centre for Vision & Vascular Science, School of Medicine, Dentistry and Biomedical Sciences, Queens’s University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK
| | - Thomas Aberle
- Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg, Germany
| | - Stephan E. Philipp
- Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg, Germany
| | - Alexander Dietrich
- Institut für Pharmakologie und Toxikologie, Medizinische Fakultät, Universität Marburg, 35043 Marburg, Germany
| | - Michael X. Zhu
- Department of Neuroscience, Biochemistry, and Center for Molecular Neurobiology, The Ohio State University, Columbus OH 43210, USA
| | - Lutz Birnbaumer
- Signal Transduction and Neurobiology Laboratories, Division of Intramural Research, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
| | - Marc Freichel
- Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg, Germany
| | - Veit Flockerzi
- Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg, Germany
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14
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Large WA, Saleh SN, Albert AP. Role of phosphoinositol 4,5-bisphosphate and diacylglycerol in regulating native TRPC channel proteins in vascular smooth muscle. Cell Calcium 2009; 45:574-82. [PMID: 19324408 DOI: 10.1016/j.ceca.2009.02.007] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2008] [Revised: 02/18/2009] [Accepted: 02/19/2009] [Indexed: 10/21/2022]
Abstract
Stimulation of receptor-operated (ROCs) and store-operated (SOCs) Ca(2+)-permeable cation channels by vasoconstrictors has many important physiological functions in vascular smooth muscle. The present review indicates that ROCs and SOCs with diverse properties in different blood vessels are likely to be explained by composition of different subunits from the canonical transient receptor potential (TRPC) family of cation channel proteins. In addition we illustrate that activation of native TRPC ROCs and SOCs involves different phospholipase-mediated transduction pathways linked to generation of diacylglycerol (DAG). Moreover we describe recent novel data showing that the endogenous phospholipid phosphoinositol 4,5-bisphosphate (PIP(2)) has profound and contrasting actions on TRPC ROCs and SOCs. Optimal activation of a native TRPC6 ROC by angiotensin II (Ang II) requires both depletion of PIP(2) and generation of DAG which leads to stimulation of TRPC6 via a PKC-independent mechanism. The data also indicate that PIP(2) has a marked constitutive inhibitory action of TRPC6 and DAG and PIP(2) are physiological antagonists on TRPC6 ROCs. In contrast PIP(2) stimulates TRPC1 SOCs and has an obligatory role in activation of these channels by store-depletion which requires PKC-dependent phosphorylation of TRPC1 proteins. Finally, we conclude that interactions between PIP(2) bound to TRPC proteins at rest, generation of DAG and PKC-dependent phosphorylation of TRPC proteins have a fundamental role in activation mechanisms of ROCs and SOCs in vascular smooth muscle.
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Affiliation(s)
- William A Large
- Ion Channels & Cell Signalling Research Centre, Division of Basic Medical Sciences, St George's, University of London, Cranmer Terrace, London, United Kingdom
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15
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Otsuguro KI, Tang J, Tang Y, Xiao R, Freichel M, Tsvilovskyy V, Ito S, Flockerzi V, Zhu MX, Zholos AV. Isoform-specific inhibition of TRPC4 channel by phosphatidylinositol 4,5-bisphosphate. J Biol Chem 2008; 283:10026-36. [PMID: 18230622 DOI: 10.1074/jbc.m707306200] [Citation(s) in RCA: 141] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Full-length transient receptor potential (TRP) cation channel TRPC4alpha and shorter TRPC4beta lacking 84 amino acids in the cytosolic C terminus are expressed in smooth muscle and endothelial cells where they regulate membrane potential and Ca(2+) influx. In common with other "classical" TRPCs, TRPC4 is activated by G(q)/phospholipase C-coupled receptors, but the underlying mechanism remains elusive. Little is also known about any isoform-specific channel regulation. Here we show that TRPC4alpha but not TRPC4beta was strongly inhibited by intracellularly applied phosphatidylinositol 4,5-bisphosphate (PIP(2)). In contrast, several other phosphoinositides (PI), including PI(3,4)P(2), PI(3,5)P(2), and PI(3,4,5)P(3), had no effect or even potentiated TRPC4alpha indicating that PIP(2) inhibits TRPC4alpha in a highly selective manner. We show that PIP(2) binds to the C terminus of TRPC4alpha but not that of TRPC4beta in vitro. Its inhibitory action was dependent on the association of TRPC4alpha with actin cytoskeleton as it was prevented by cytochalasin D treatment or by the deletion of the C-terminal PDZ-binding motif (Thr-Thr-Arg-Leu) that links TRPC4 to F-actin through the sodium-hydrogen exchanger regulatory factor and ezrin. PIP(2) breakdown appears to be a required step in TRPC4alpha channel activation as PIP(2) depletion alone was insufficient for channel opening, which additionally required Ca(2+) and pertussis toxin-sensitive G(i/o) proteins. Thus, TRPC4 channels integrate a variety of G-protein-dependent stimuli, including a PIP(2)/cytoskeleton dependence reminiscent of the TRPC4-like muscarinic agonist-activated cation channels in ileal myocytes.
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Affiliation(s)
- Ken-ichi Otsuguro
- Cardiovascular Biomedical Research Centre, School of Medicine and Dentistry, Queen's University Belfast, Belfast, United Kingdom
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16
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Yamamoto M, Unno T, Matsuyama H, Kohda M, Masuda N, Nishimura M, Ishii T, Komori S. Two Types of Cation Channel Activated by Stimulation of Muscarinic Receptors in Guinea-Pig Urinary Bladder Smooth Muscle. J Pharmacol Sci 2008; 108:248-57. [DOI: 10.1254/jphs.08138fp] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
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17
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Trailovic SM, Verma S, Clark CL, Robertson AP, Martin RJ. Effects of the muscarinic agonist, 5-methylfurmethiodide, on contraction and electrophysiology of Ascaris suum muscle. Int J Parasitol 2007; 38:945-57. [PMID: 18206155 DOI: 10.1016/j.ijpara.2007.11.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2007] [Revised: 11/01/2007] [Accepted: 11/18/2007] [Indexed: 11/25/2022]
Abstract
Contraction and electrophysiological effects of 5-methylfurmethiodide (MFI), a selective muscarinic agonist in mammals, were tested on Ascaris suum muscle strips. In a contraction assay, MFI produced weak contraction and was less potent than levamisole and acetylcholine. Atropine (3microM) a non-selective muscarinic antagonist in mammalian preparations, did not affect contractions produced by MFI. Mecamylamine (3microM) a nicotinic antagonist in A. suum preparations, blocked the MFI contractions indicating that MFI had weak nicotinic agonist actions. In two-micropipette current-clamp experiments MFI, at concentrations greater than 10microM, produced concentration-dependent depolarizations and small increases in membrane conductance. The depolarizing effects were not abolished by perfusing the preparation in a calcium-free Ascaris Ringer solution to block synaptic transmission, suggesting that MFI effects were mediated by receptors on the muscle and were calcium-independent. A high concentration of mecamylamine, 30microM, only reduced the depolarizing responses by 42%, indicating that MFI also had effects on non-nicotinic receptors. Three non-nicotinic effects in the presence of 30microM mecamylamine were identified using voltage-clamp techniques: (i) MFI produced opening of mecamylamine-resistant non-selective-cation channel currents; (ii) MFI inhibited opening of voltage-activated potassium currents; and (iii) MFI increased the threshold of voltage-activated calcium currents. We suggest that a drug that is more selective for voltage-activated potassium currents, without effects on other channels like MFI, may be exploited pharmacologically as a novel anthelmintic or as an agent to potentiate the action of levamisole. In a larval migration assay we demonstrated that 4-aminopyridine (4-AP: a potassium channel blocker) potentiated the effects of levamisole but MFI did not.
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Affiliation(s)
- Sasa M Trailovic
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011-1250, USA
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18
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Gordienko DV, Harhun MI, Kustov MV, Pucovský V, Bolton TB. Sub-plasmalemmal [Ca2+]i upstroke in myocytes of the guinea-pig small intestine evoked by muscarinic stimulation: IP3R-mediated Ca2+ release induced by voltage-gated Ca2+ entry. Cell Calcium 2007; 43:122-41. [PMID: 17570487 PMCID: PMC2268754 DOI: 10.1016/j.ceca.2007.04.012] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2007] [Revised: 03/29/2007] [Accepted: 04/20/2007] [Indexed: 11/23/2022]
Abstract
Membrane depolarization triggers Ca2+ release from the sarcoplasmic reticulum (SR) in skeletal muscles via direct interaction between the voltage-gated L-type Ca2+ channels (the dihydropyridine receptors; VGCCs) and ryanodine receptors (RyRs), while in cardiac muscles Ca2+ entry through VGCCs triggers RyR-mediated Ca2+ release via a Ca2+-induced Ca2+ release (CICR) mechanism. Here we demonstrate that in phasic smooth muscle of the guinea-pig small intestine, excitation evoked by muscarinic receptor activation triggers an abrupt Ca2+ release from sub-plasmalemmal (sub-PM) SR elements enriched with inositol 1,4,5-trisphosphate receptors (IP3Rs) and poor in RyRs. This was followed by a lesser rise, or oscillations in [Ca2+]i. The initial abrupt sub-PM [Ca2+]i upstroke was all but abolished by block of VGCCs (by 5 μM nicardipine), depletion of intracellular Ca2+ stores (with 10 μM cyclopiazonic acid) or inhibition of IP3Rs (by 2 μM xestospongin C or 30 μM 2-APB), but was not affected by block of RyRs (by 50–100 μM tetracaine or 100 μM ryanodine). Inhibition of either IP3Rs or RyRs attenuated phasic muscarinic contraction by 73%. Thus, in contrast to cardiac muscles, excitation–contraction coupling in this phasic visceral smooth muscle occurs by Ca2+ entry through VGCCs which evokes an initial IP3R-mediated Ca2+ release activated via a CICR mechanism.
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Affiliation(s)
- D V Gordienko
- Division of Basic Medical Sciences, Ion Channels and Cell Signalling Centre, St. George's University of London, UK.
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19
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Sakamoto T, Unno T, Kitazawa T, Taneike T, Yamada M, Wess J, Nishimura M, Komori S. Three distinct muscarinic signalling pathways for cationic channel activation in mouse gut smooth muscle cells. J Physiol 2007; 582:41-61. [PMID: 17463038 PMCID: PMC2075272 DOI: 10.1113/jphysiol.2007.133165] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Using mutant mice genetically lacking certain subtypes of muscarinic receptor, we have studied muscarinic signal pathways mediating cationic channel activation in intestinal smooth muscle cells. In cells from M2 subtype-knockout (M2-KO) or M3-KO mice, carbachol (100 microM) evoked a muscarinic cationic current (mI(Cat)) as small as approximately 10% of mI(Cat) in wild-type (WT) cells. No appreciable current was evoked in M2/M3 double-KO cells. All mutant type cells preserved normal G-protein-cationic channel coupling. The M3-KO and WT mI(Cat) each showed a U-shaped current-voltage (I-V) relationship, whereas the M2-KO mI(Cat) displayed a linear I-V relationship. Channel analysis in outside-out patches recognized 70-pS and 120-pS channels as the major muscarinic cationic channels. Active patches of M2-KO cells exhibited both 70-pS and 120-pS channel activity usually together, either of which consisted of brief openings (the respective mean open times O(tau) = 0.55 and 0.23 ms). In contrast, active M3-KO patches showed only 70-pS channel activity, which had three open states (O(tau) = 0.55, 3.1 and 17.4 ms). In WT patches, besides the M2-KO and M3-KO types, another type of channel activity was also observed that consisted of 70-pS channel openings with four open states (O(tau) = 0.62, 2.7, 16.9 and 121.1 ms), and patch current of this channel activity showed a U-shaped I-V curve similar to the WT mI(Cat). The present results demonstrate that intestinal myocytes are endowed with three distinct muscarinic pathways mediating cationic channel activation and that the M2/M3 pathway targeting 70-pS channels, serves as the major contributor to mI(Cat) generation. The delineation of this pathway is consistent with the formation of a functional unit by the M2-Go protein and the M3-PLC systems predicted to control cationic channels.
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MESH Headings
- Animals
- Carbachol/pharmacology
- Cations/metabolism
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- Guanosine 5'-O-(3-Thiotriphosphate)/pharmacology
- Ileum/cytology
- Ileum/drug effects
- Ileum/metabolism
- In Vitro Techniques
- Ion Channel Gating
- Ion Channels/chemistry
- Ion Channels/metabolism
- Jejunum/cytology
- Jejunum/drug effects
- Jejunum/metabolism
- Kinetics
- Membrane Potentials
- Mice
- Mice, Knockout
- Models, Molecular
- Muscarinic Agonists/pharmacology
- Muscle, Smooth/cytology
- Muscle, Smooth/drug effects
- Muscle, Smooth/metabolism
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/metabolism
- Patch-Clamp Techniques
- Protein Conformation
- Receptor, Muscarinic M2/agonists
- Receptor, Muscarinic M2/deficiency
- Receptor, Muscarinic M2/genetics
- Receptor, Muscarinic M2/metabolism
- Receptor, Muscarinic M3/agonists
- Receptor, Muscarinic M3/deficiency
- Receptor, Muscarinic M3/genetics
- Receptor, Muscarinic M3/metabolism
- Signal Transduction
- Type C Phospholipases/metabolism
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Affiliation(s)
- Takashi Sakamoto
- Department of Pathogenetic Veterinary Science, United Graduate School of Veterinary Science, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
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20
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Saleh SN, Albert AP, Peppiatt CM, Large WA. Angiotensin II activates two cation conductances with distinct TRPC1 and TRPC6 channel properties in rabbit mesenteric artery myocytes. J Physiol 2006; 577:479-95. [PMID: 16973707 PMCID: PMC1890440 DOI: 10.1113/jphysiol.2006.119305] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Angiotensin II (Ang II) is a potent vasoconstrictor with an important role in controlling blood pressure; however, there is little information on cellular mechanisms underlying Ang II-evoked vasoconstrictor responses. The aim of the present study is to investigate the effect of Ang II on cation conductances in freshly dispersed rabbit mesenteric artery myocytes at the single-channel level using patch-clamp techniques. In cell-attached patches, bath application of low concentrations of Ang II (1 nM) activated cation channel currents (Icat1) with conductances states of about 15, 30 and 45 pS. At relatively high concentrations, Ang II (100 nM) inhibited Icat1 but evoked another cation channel (Icat2) with a conductance of approximately 2 pS. Ang II-evoked Icat1 and Icat2 were inhibited by the AT1 receptor antagonist losartan and the phospholipase C (PLC) inhibitor U73122. The diacylglycerol (DAG) lipase inhibitor RHC80267 initially induced Icat1 which was subsequently inhibited to reveal Icat2. The DAG analogue 1-oleoyl-2-acetyl-sn-glycerol (1 microM) activated Icat1 and Icat2 but inositol 1,4,5-trisphosphate did not evoke either conductance. The protein kinase C (PKC) inhibitor chelerythrine (3 microM) potentiated Ang II-evoked Icat1 and inhibited Icat2 whereas the PKC activator phorbol-12,13-dibutyrate (1 microM) reduced Ang II-induced Icat1 but activated Icat2. Moreover in cell-attached patches pretreated with chelerythrine, application of 100 nM Ang II activated Icat1. These data indicate that PKC inhibits Icat1 but stimulates Icat2. Agents that deplete intracellular Ca2+ stores also activated cation channel currents with similar properties to Icat2. Bath application of anti-TRPC6 and anti-TRPC1 antibodies to inside-out patches inhibited Icat1 and Icat2, respectively. Also flufenamic acid and zero external Ca2+ concentration, respectively, potentiated and reduced Ang II-evoked Icat1. Immunocytochemical studies showed TRPC6 and TRPC1 expression with TRPC6 preferentially distributed in the plasma membrane and TRPC1 expression located throughout the myocyte. These results indicate that Ang II activates two distinct cation conductances in mesenteric artery myocytes by stimulation of AT1 receptors linked to PLC. Icat1 is activated by DAG via a PKC-independent mechanism whereas Icat2 involves DAG acting via a PKC-dependent pathway. Higher concentrations of Ang II inhibit Icat1 by activating an inhibitory effect of PKC. It is proposed that TRPC6 and TRPC1 channel proteins are important components of Ang II-induced Icat1 and Icat2, respectively.
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MESH Headings
- Alkaloids/pharmacology
- Angiotensin II/metabolism
- Angiotensin II/pharmacology
- Animals
- Antibodies/pharmacology
- Benzophenanthridines/pharmacology
- Calcium/metabolism
- Diglycerides/metabolism
- Dose-Response Relationship, Drug
- Enzyme Activators/pharmacology
- Enzyme Inhibitors/pharmacology
- Estrenes/pharmacology
- Flufenamic Acid/pharmacology
- Immunohistochemistry
- In Vitro Techniques
- Ion Channel Gating/drug effects
- Membrane Potentials/drug effects
- Mesenteric Arteries/drug effects
- Muscle, Smooth, Vascular/chemistry
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Myocytes, Smooth Muscle/chemistry
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/metabolism
- Phorbol 12,13-Dibutyrate/pharmacology
- Protein Kinase C/antagonists & inhibitors
- Protein Kinase C/metabolism
- Pyrrolidinones/pharmacology
- Rabbits
- Receptor, Angiotensin, Type 1/drug effects
- Signal Transduction/drug effects
- TRPC Cation Channels/analysis
- TRPC Cation Channels/drug effects
- TRPC Cation Channels/immunology
- TRPC Cation Channels/metabolism
- Time Factors
- Type C Phospholipases/antagonists & inhibitors
- Type C Phospholipases/metabolism
- Vasoconstrictor Agents/metabolism
- Vasoconstrictor Agents/pharmacology
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Affiliation(s)
- S N Saleh
- Ion Channels and Cell Signalling, Division of Basic Medical Sciences, St George's, University of London, Cranmer Terrace, London SW17 ORE, UK
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21
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Brann JH, Fadool DA. Vomeronasal sensory neurons from Sternotherus odoratus (stinkpot/musk turtle) respond to chemosignals via the phospholipase C system. ACTA ACUST UNITED AC 2006; 209:1914-27. [PMID: 16651557 PMCID: PMC2779218 DOI: 10.1242/jeb.02206] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The mammalian signal transduction apparatus utilized by vomeronasal sensory neurons (VSNs) in the vomeronasal organ (VNO) has been richly explored, while that of reptiles, and in particular, the stinkpot or musk turtle Sternotherus odoratus, is less understood. Given that the turtle's well-known reproductive and mating behaviors are governed by chemical communication, 247 patch-clamp recordings were made from male and female S. odoratus VSNs to study the chemosignal-activated properties as well as the second-messenger system underlying the receptor potential. Of the total neurons tested, 88 (35%) were responsive to at least one of five complex natural chemicals, some of which demonstrated a degree of sexual dimorphism in response selectivity. Most notably, male VSNs responded to male urine with solely outward currents. Ruthenium Red, an IP3 receptor (IP3R) antagonist, failed to block chemosignal-activated currents, while the phospholipase C (PLC) inhibitor, U73122, abolished the chemosignal-activated current within 2 min, implicating the PLC system in the generation of a receptor potential in the VNO of musk turtles. Dialysis of several second messengers or their analogues failed to elicit currents in the whole-cell patch-clamp configuration, negating a direct gating of the transduction channel by cyclic adenosine monophosphate (cAMP), inositol 1,4,5-trisphosphate (IP3), arachidonic acid (AA), or diacylglycerol (DAG). Reversal potential analysis of chemosignal-evoked currents demonstrated that inward currents reversed at -5.7+/-7.8 mV (mean +/- s.e.m.; N=10), while outward currents reversed at -28.2+/-2.4 mV (N=30). Measurements of conductance changes associated with outward currents indicated that the outward current represents a reduction of a steady state inward current by the closure of an ion channel when the VSN is exposed to a chemical stimulus such as male urine. Chemosignal-activated currents were significantly reduced when a peptide mimicking a domain on canonical transient receptor potential 2 (TRPC2), to which type 3 IP3 receptor (IP3R3) binds, was included in the recording pipette. Collectively these data suggest that there are multiple transduction cascades operational in the VSNs of S. odoratus, one of which may be mediated by a non-selective cation conductance that is not gated by IP3 but may be modulated by the interaction of its receptor with the TRPC2 channel.
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Affiliation(s)
- Jessica H. Brann
- The Florida State University, Department of Biological Science, Program in Neuroscience, Biomedical Research Facility, Tallahassee, FL 32306, USA
| | - Debra A. Fadool
- The Florida State University, Department of Biological Science, Program in Neuroscience, Biomedical Research Facility, Tallahassee, FL 32306, USA
- The Florida State University, Department of Biological Science, Program in Molecular Biophysics, Biomedical Research Facility, Tallahassee, FL 32306, USA
- Author for correspondence (e-mail: )
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22
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Zholos AV. Regulation of TRP-like muscarinic cation current in gastrointestinal smooth muscle with special reference to PLC/InsP3/Ca2+ system. Acta Pharmacol Sin 2006; 27:833-42. [PMID: 16787566 DOI: 10.1111/j.1745-7254.2006.00392.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Acetylcholine, the main enteric excitatory neuromuscular transmitter, evokes membrane depolarization and contraction of gastrointestinal smooth muscle cells by activating G protein-coupled muscarinic receptors. Although the cholinergic excitation is generally underlined by the multiplicity of ion channel effects, the primary event appears to be the opening of cation-selective channels; among them the 60 pS channel has been recently identified as the main target for the acetylcholine action in gastrointestinal myocytes. The evoked cation current, termed mI(CAT), causes either an oscillatory or a more sustained membrane depolarization response, which in turn leads to increases of the open probability of voltage-gated Ca2+ channels, thus providing Ca2+ entry in parallel with Ca2+ release for intracellular Ca2+ concentration rise and contraction. In recent years there have been several significant developments in our understanding of the signaling processes underlying mICAT generation. They have revealed important synergistic interactions between M2 and M3 receptor subtypes, single channel mechanisms, and the involvement of TRPC-encoded proteins as essential components of native muscarinic cation channels. This review summarizes these recent findings and in particular discusses the roles of the phospholipase C/InsP3/intracellular Ca2+ release system in the mI(CAT) physiological regulation.
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23
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Unno T, Matsuyama H, Okamoto H, Sakamoto T, Yamamoto M, Tanahashi Y, Yan HD, Komori S. Muscarinic cationic current in gastrointestinal smooth muscles: signal transduction and role in contraction. ACTA ACUST UNITED AC 2006; 26:203-17. [PMID: 16879487 DOI: 10.1111/j.1474-8673.2006.00366.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
1 The muscarinic receptor plays a key role in the parasympathetic nervous control of various peripheral tissues including gastrointestinal tract. The neurotransmitter acetylcholine, via activating muscarinic receptors that exist in smooth muscle, produces its contraction. 2 There is the opening of cationic channels as an underlying mechanism. The opening of cationic channels results in influxes of Ca2+ via the channels into the cell and also via voltage-dependent Ca2+ channels which secondarily opened in response to the depolarization, providing an amount of Ca2+ for activation of the contractile proteins. 3 Electrophysiological and pharmacological studies have shown that the cationic channels as well as muscarinic receptors exist in many visceral smooth muscle cells. However, the activation mechanisms of the cationic channels are still unclear. 4 In this article, we summarize the current knowledge of the muscarinic receptor-operated cationic channels, focusing on the receptor subtype, G protein and other signalling molecules that are involved in activation of these channels and on the molecular characteristics of the channel. This will improve strategies aimed at developing new selective pharmacological agents and understanding the activation mechanism and functions of these channels in physiological systems.
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Affiliation(s)
- T Unno
- Laboratory of Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Science, Gifu University, Gifu 501-1193, Japan
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24
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Si XM, Huang L, Lv P, Xia H, Luo HS. Effects of cholecystokinin-8 induced gastric dysmotility on bile regurgitation during stress and molecular mechanisms. ACTA ACUST UNITED AC 2006; 136:64-71. [PMID: 16814406 DOI: 10.1016/j.regpep.2006.04.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2005] [Revised: 04/22/2006] [Accepted: 04/28/2006] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To illustrate the existence of bile regurgitation under stress condition, and explore the possible effects and related mechanism of changes of plasma cholecystokinin octapeptide (CCK-8) and intragastric pH on stress-induced bile regurgitation in rats. METHODS (1) Changes in plasma CCK-8 and gastric bile concentration were respectively measured by using radioimmunoassay (RIA) method while simultaneously calculating gastric ulcer index (UI) and intragastric pH; (2) Each isolated gastric strips were suspended in a tissue chamber to record the contractile responses by polyphysiograph; (3) The responsiveness of gastric smooth muscle cells (SMCs) to sulfated cholecystokinin octapeptide (CCK-8S) were examined using fura-2-loaded microfluorimetric measurement of intracellular calcium concentration ([Ca(2+)]i); (4) The current of L-type calcium channels (I(CaL)) of SMCs were recorded by patch clamp techniques. RESULTS (1) Compared with the normal control group, plasma CCK-8 and gastric bile concentration significantly increased during stress (p<0.01) and both simultaneously reached the peak at the time point of 2 h after stress; UI and intragastric pH apparently increased (p<0.01); (2) Significant changes to CCK-8S were found in the mean contractile amplitude and frequency of circular muscle (CM) and longitudinal muscle (LM) of gastric antrum and pylorus; (3) CCK-8S-evoked significant increase in [Ca(2+)]i (p<0.01) could be suppressed by CCK-A receptor (CCK-AR) antagonist; whereas a small but significant increase was still elicited by CCK-8S under condition of the removal of extracellular calcium or by given nifidipine; (4) CCK-8S-intensified calcium current (I(CaL)) apparently inhibited by respective administration of nifidipine, Ca(2+)-ATPase inhibitors or calcium dependent chloride channel (I(Cl-Ca)) blocker (p<0.01). CONCLUSION Gastric mucosal damage induced by bile regurgitation is closely connected with gastric antrum and pylorus dysmotility evoked by CCK-8 during the stress. CCK-8S-evoked [Ca(2+)]i increase in gastric antrum and pylorus SMC depends on the release of intracellular calcium stores which activates L-type voltage-dependent calcium channels (VDCC) through the activation of calcium dependent chloride channels.
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Affiliation(s)
- Xin-Min Si
- Department of Digestive Medicine, RenMin Hospital of WuHan University, HuBei, 430060, China
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Balemba OB, Salter MJ, Heppner TJ, Bonev AD, Nelson MT, Mawe GM. Spontaneous electrical rhythmicity and the role of the sarcoplasmic reticulum in the excitability of guinea pig gallbladder smooth muscle cells. Am J Physiol Gastrointest Liver Physiol 2006; 290:G655-64. [PMID: 16293655 DOI: 10.1152/ajpgi.00310.2005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Spontaneous action potentials and Ca(2+) transients were investigated in intact gallbladder preparations to determine how electrical events propagate and the cellular mechanisms that modulate these events. Rhythmic phasic contractions were preceded by Ca(2+) flashes that were either focal (limited to one or a few bundles), multifocal (occurring asynchronously in several bundles), or global (simultaneous flashes throughout the field). Ca(2+) flashes and action potentials were abolished by inhibiting sarcoplasmic reticulum (SR) Ca(2+) release via inositol (1,4,5)-trisphosphate [Ins(1,4,5)P(3)] channels with 2-aminoethoxydiphenyl borate and xestospongin C or by inhibiting voltage-dependent Ca(2+) channels (VDCCs) with nifedipine or diltiazem or nisoldipine. Inhibiting ryanodine channels with ryanodine caused multiple spikes superimposed upon plateaus of action potentials and extended quiescent periods. Depletion of SR Ca(2+) stores with thapsigargin or cyclopiazonic acid increased the frequency and duration of Ca(2+) flashes and action potentials. Acetylcholine, carbachol, or cholecystokinin increased synchronized and increased the frequency of Ca(2+) flashes and action potentials. The phospholipase C (PLC) inhibitor U-73122 did not affect Ca(2+) flash or action potential activity but inhibited the excitatory effects of acetylcholine on these events. These results indicate that Ca(2+) flashes correspond to action potentials and that rhythmic excitation in the gallbladder is multifocal among gallbladder smooth muscle bundles and can be synchronized by excitatory agonists. These events do not depend on PLC activation, but agonist stimulation involves activation of PLC. Generation of these events depends on Ca(2+) entry via VDCCs and on Ca(2+) mobilization from the SR via Ins(1,4,5)P(3) channels.
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Affiliation(s)
- Onesmo B Balemba
- Department of Anatomy and Neurobiology, University of Vermont, Burlington, 05405, USA
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Sakamoto T, Unno T, Matsuyama H, Uchiyama M, Hattori M, Nishimura M, Komori S. Characterization of muscarinic receptor-mediated cationic currents in longitudinal smooth muscle cells of mouse small intestine. J Pharmacol Sci 2006; 100:215-26. [PMID: 16538027 DOI: 10.1254/jphs.fp0050973] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
In mouse intestinal smooth muscle cells held at -50 mV, carbachol evoked an atropine-sensitive inward current in the intracellular presence of Cs(+). The current response consisted of an initial peak followed by a smaller plateau component on which oscillatory currents frequently arose. Results from various experimental procedures indicated that the inward current is a muscarinic receptor-operated cationic current (mI(cat)) sensitive to cytosolic Ca(2+) concentration ([Ca(2+)](i)) and that the initial peak and oscillatory components are contaminated by Ca(2+)-activated Cl(-) currents. Under conditions of [Ca(2+)](i) buffered to 100 nM, the mI(cat) response to cumulative carbachol applications was inhibited competitively by an M(2)-selective antagonist but non-competitively by an M(3)-selective one. Also it was severely reduced by pertussis toxin (PTX) treatment or a phospholipase C (PLC) inhibitor. Comparative analysis of mI(cat) in mouse and guinea-pig intestinal myocytes indicated that the underlying channels resemble between those myocytes in agonist sensitivity, current-voltage relationship, and unitary conductance. The results suggest that in mouse intestinal myocytes, mI(cat) arises mainly via an M(2)/M(3) synergistic mechanism involving PTX-sensitive G-proteins and PLC activity in the absence of current modulation by [Ca(2+)](i) changes, as described for guinea-pig ileal mI(cat). The channels underlying mI(cat) are also indistinguishable in gating properties between both types of myocytes.
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Affiliation(s)
- Takashi Sakamoto
- Department of Pathogenic Veterinary Science, United Graduate School of Veterinary Science, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
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Kustov MV, Tsvilovskii VV, Zholos AV, Shuba MF, Bolton TB. Peculiarities of phospholipase C-dependent release of CA2+ from intracellular stores upon activation of choline and purine receptors in myocytes of the guinea-pig small intestine. NEUROPHYSIOLOGY+ 2006. [DOI: 10.1007/s11062-006-0019-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Gordienko DV, Zholos AV. Regulation of muscarinic cationic current in myocytes from guinea-pig ileum by intracellular Ca2+ release: a central role of inositol 1,4,5-trisphosphate receptors. Cell Calcium 2005; 36:367-86. [PMID: 15451621 DOI: 10.1016/j.ceca.2004.02.021] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2003] [Revised: 02/11/2004] [Accepted: 02/14/2004] [Indexed: 11/26/2022]
Abstract
The dynamics of carbachol (CCh)-induced [Ca(2+)](i) changes was related to the kinetics of muscarinic cationic current (mI(cat)) and the effect of Ca(2+) release through ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate receptors (IP(3)Rs) on mI(cat) was evaluated by fast x-y or line-scan confocal imaging of [Ca(2+)](i) combined with simultaneous recording of mI(cat) under whole-cell voltage clamp. When myocytes freshly isolated from the longitudinal layer of the guinea-pig ileum were loaded with the Ca(2+)-sensitive indicator fluo-3, x-y confocal imaging revealed CCh (10 microM)-induced Ca(2+) waves, which propagated from the cell ends towards the myocyte centre at 45.9 +/- 8.8 microms(-1) (n = 13). Initiation of the Ca(2+) wave preceded the appearance of any measurable mI(cat) by 229 +/- 55 ms (n = 7). Furthermore, CCh-induced [Ca(2+)](i) transients peaked 1.22 +/- 0.11s (n = 17) before mI(cat) reached peak amplitude. At -50 mV, spontaneous release of Ca(2+) through RyRs, resulting in Ca(2+) sparks, had no effect on CCh-induced mI(cat) but activated BK channels leading to spontaneous transient outward currents (STOCs). In addition, Ca(2+) release through RyRs induced by brief application of 5 mM caffeine was initiated at the cell centre but did not augment mI(cat) (n = 14). This was not due to an inhibitory effect of caffeine on muscarinic cationic channels (since application of 5 mM caffeine did not inhibit mI(cat) when [Ca(2+)](i) was strongly buffered with Ca(2+)/BAPTA buffer) nor was it due to an effect of caffeine on other mechanisms possibly involved in the regulation of Ca(2+) sensitivity of muscarinic cationic channels (since in the presence of 5 mM caffeine, photorelease of Ca(2+) upon cell dialysis with 5 mM NP-EGTA/3.8 mM Ca(2+) potentiated mI(cat) in the same way as in control). In contrast, IP(3)R-mediated Ca(2+) release upon flash photolysis of "caged" IP(3) (30 microM in the pipette solution) augmented mI(cat) (n = 15), even though [Ca(2+)](i) did not reach the level required for potentiation of mI(cat) during photorelease of Ca(2+) (n = 10). Intracellular calcium stores were visualised by loading of the myocytes with the low-affinity Ca(2+) indicator fluo-3FF AM and consisted of a superficial sarcoplasmic reticulum (SR) network and some perinuclear formation, which appeared to be continuous with the superficial SR. Immunostaining of the myocytes with antibodies to IP(3)R type 1 and to RyRs revealed that IP(3)Rs are predominant in the superficial SR while RyRs are confined to the central region of the cell. These results suggest that IP(3)R-mediated Ca(2+) release plays a central role in the modulation of mI(cat) in the guinea-pig ileum and that IP(3) may sensitise the regulatory mechanisms of the muscarinic cationic channels gating to Ca(2+).
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Affiliation(s)
- D V Gordienko
- Department of Basic Medical Sciences/Pharmacology, St. George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK.
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Eglen RM. Muscarinic Receptor Subtype Pharmacology and Physiology. PROGRESS IN MEDICINAL CHEMISTRY 2005; 43:105-36. [PMID: 15850824 DOI: 10.1016/s0079-6468(05)43004-0] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Affiliation(s)
- Richard M Eglen
- DiscoveRx Corporation, Albrae Street, Fremont, CA 94538, USA
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Zholos AV, Zholos AA, Bolton TB. G-protein-gated TRP-like cationic channel activated by muscarinic receptors: effect of potential on single-channel gating. ACTA ACUST UNITED AC 2004; 123:581-98. [PMID: 15111646 PMCID: PMC2234496 DOI: 10.1085/jgp.200309002] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
There is little information about the mechanisms by which G-protein–coupled receptors gate ion channels although many ionotropic receptors are well studied. We have investigated gating of the muscarinic cationic channel, which mediates the excitatory effect of acetylcholine in smooth muscles, and proposed a scheme consisting of four pairs of closed and open states. Channel kinetics appeared to be the same in cell-attached or outside-out patches whether the channel was activated by carbachol application or by intracellular dialysis with GTPγS. Since in the latter case G-proteins are permanently active, it is concluded that the cationic channel is the major determinant of its own gating, similarly to the KACh channel (Ivanova-Nikolova, T.T., and G.E. Breitwieser. 1997. J. Gen. Physiol. 109:245–253). Analysis of adjacent-state dwell times revealed connections between the states that showed features conserved among many other ligand-gated ion channels (e.g., nAChR, BKCa channel). Open probability (PO) of the cationic channel was increased by membrane depolarization consistent with the prominent U-shaped I-V relationship of the muscarinic whole-cell current at negative potentials. Membrane potential affected transitions within each closed-open state pair but had little effect on transitions between pairs; thus, the latter are likely to be caused by interactions of the channel with its ligands, e.g., Ca2+ and Gαo-GTP. Channel activity was highly heterogeneous, as was evident from the prominent cycling behavior when PO was measured over 5-s intervals. This was related to the variable frequency of openings (as in the KACh channel) and, especially, to the number of long openings between consecutive long shuttings. Analysis of the underlying Markov chain in terms of probabilities allowed us to evaluate the contribution of each open state to the integral current (from shortest to longest open state: 0.1, 3, 24, and 73%) as PO increased 525-fold in three stages.
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Affiliation(s)
- Alexander V Zholos
- Laboratory of Molecular Pharmacology of Cellular Receptors and Ion Channels, A.A. Bogomoletz Institute of Physiology, Kiev, 01024 Ukraine.
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Ford CP, Stemkowski PL, Smith PA. Possible role of phosphatidylinositol 4,5, bisphosphate in luteinizing hormone releasing hormone-mediated M-current inhibition in bullfrog sympathetic neurons. Eur J Neurosci 2004; 20:2990-8. [PMID: 15579153 DOI: 10.1111/j.1460-9568.2004.03786.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Luteinizing hormone releasing hormone (LHRH) is a physiological modulator of neuronal excitability in bullfrog sympathetic ganglia (BFSG). Actions of LHRH involve suppression of the noninactivating, voltage-dependent M-type K+ channel conductance (gM). We found, using whole-cell recordings from these neurons, that LHRH-induced suppression of gM was attenuated by the phospholipase C (PLC) inhibitor U73122 (10 microM) but not by the inactive isomer U73343 (10 microM). Buffering internal Ca2+ to 117 nM with intracellular 20 mM BAPTA + 8 mM Ca2+ or to < 10 nM with intracellular 20 mM BAPTA + 0.4 mM Ca2+ did not attenuate LHRH-induced gM suppression. Suppression of gM by LHRH was not antagonized by the inositol 1,4,5 trisphosphate (InsP3) receptor antagonist heparin (approximately 300 microM). Preventing phosphatidylinositol-4,5-bisphosphate (PIP2) synthesis by blocking phosphatidylinositol-4-kinase with wortmannin (10 microM) or with the nonhydrolysable ATP analogue AMP-PNP (3 mM) prolonged recovery of LHRH-induced gM suppression. This effect was not produced by blocking phosphatidyl inositol-3-kinase with LY294002 (10 microM). Rundown of gM was attenuated when cells were dialysed with 240 microM di-octanoyl PIP2 or 240 microM di-octanoyl phosphatidylinositol-3,4,5-trisphosphate (PIP3) but not with 240 microM di-octanoyl phosphatidylcholine. LHRH-induced gM suppression was competitively antagonized by dialysis with 240 microM di-octanoyl PIP2, but not with di-octanoyl phosphatidylcholine. These results would be expected if LHRH-induced gM suppression reflects a PLC-mediated decrease in plasma membrane PIP2 levels.
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Affiliation(s)
- Christopher P Ford
- Centre for Neuroscience and Department of Pharmacology, 9.75 Medical Sciences Building, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada
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Tsvilovskyy VV, Zholos AV, Bolton TB. Effects of polyamines on the muscarinic receptor-operated cation current in guinea-pig ileal smooth muscle myocytes. Br J Pharmacol 2004; 143:968-75. [PMID: 15557285 PMCID: PMC1575962 DOI: 10.1038/sj.bjp.0706010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The effects of extracellular and intracellular polyamines (PAs), spermine and putrescine, on the cation current (mI(CAT)) evoked either by activating muscarinic receptors with carbachol or by intracellularly applied GTPgammaS (in the absence of carbachol) were studied using patch-clamp recording techniques in single guinea-pig ileal myocytes. Extracellular spermine and putrescine rapidly and reversibly inhibited mI(CAT) in a concentration- and voltage-dependent manner with the IC(50) values at -40 mV of about 1 and 5 mM, respectively. Membrane depolarization relieved the blocking action of PAs although cation conductance activation curve remained N-shaped. The inhibition was similar for both carbachol- and GTPgammaS-evoked currents, suggesting that the cation channel rather than the muscarinic receptor was the primary site of the PA action. In outside-out membrane patches, both cation channel unitary conductance and open probability were reduced. In perforated-patch experiments used to retain cytoplasmic PAs sustained 100 microM carbachol-induced mI(CAT) was significantly smaller (478 +/- 76 pA, n = 7) compared to that recorded using conventional whole-cell configuration with nominally PA-free pipette solution (1314 +/- 76 pA, n = 12), but comparable in size to mI(CAT) with 0.3 mM spermine in the pipette solution (509 +/- 41 pA, n = 19). Intracellular putrescine inhibited mI(CAT) less potently compared to spermine. In conclusion, these results show a novel role of intestinal PAs in mI(CAT) inhibition, which can contribute to their well-known suppressing effect on the gastrointestinal smooth muscle excitability and contractility.
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Affiliation(s)
- Volodymyr V Tsvilovskyy
- Laboratory of Molecular Pharmacology of Cellular Receptors and Ion Channels, A.A. Bogomoletz Institute of Physiology, Kiev, 01024 Ukraine
| | - Alexander V Zholos
- Laboratory of Molecular Pharmacology of Cellular Receptors and Ion Channels, A.A. Bogomoletz Institute of Physiology, Kiev, 01024 Ukraine
- Author for correspondence:
| | - Thomas B Bolton
- Department of Basic Medical Sciences/Pharmacology, St. George's Hospital Medical School, London SW17 0RE
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Beech DJ, Muraki K, Flemming R. Non-selective cationic channels of smooth muscle and the mammalian homologues of Drosophila TRP. J Physiol 2004; 559:685-706. [PMID: 15272031 PMCID: PMC1665181 DOI: 10.1113/jphysiol.2004.068734] [Citation(s) in RCA: 196] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2004] [Accepted: 07/20/2004] [Indexed: 12/25/2022] Open
Abstract
Throughout the body there are smooth muscle cells controlling a myriad of tubes and reservoirs. The cells show enormous diversity and complexity compounded by a plasticity that is critical in physiology and disease. Over the past quarter of a century we have seen that smooth muscle cells contain--as part of a gamut of ion-handling mechanisms--a family of cationic channels with significant permeability to calcium, potassium and sodium. Several of these channels are sensors of calcium store depletion, G-protein-coupled receptor activation, membrane stretch, intracellular Ca2+, pH, phospholipid signals and other factors. Progress in understanding the channels has, however, been hampered by a paucity of specific pharmacological agents and difficulty in identifying the underlying genes. In this review we summarize current knowledge of these smooth muscle cationic channels and evaluate the hypothesis that the underlying genes are homologues of Drosophila TRP (transient receptor potential). Direct evidence exists for roles of TRPC1, TRPC4/5, TRPC6, TRPV2, TRPP1 and TRPP2, and more are likely to be added soon. Some of these TRP proteins respond to a multiplicity of activation signals--promiscuity of gating that could enable a variety of context-dependent functions. We would seem to be witnessing the first phase of the molecular delineation of these cationic channels, something that should prove a leap forward for strategies aimed at developing new selective pharmacological agents and understanding the activation mechanisms and functions of these channels in physiological systems.
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Affiliation(s)
- D J Beech
- School of Biomedical Sciences, University of Leeds, LS2 9JT, UK.
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Zholos AV, Bolton TB, Dresvyannikov AV, Kustov MV, Tsvilovskii VV, Shuba MF. Cholinergic excitation of smooth muscles: Multiple signaling pathways linking M2 and M3 muscarinic receptors to cationic channels. NEUROPHYSIOLOGY+ 2004. [DOI: 10.1007/s11062-005-0034-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Adenylate cyclase-mediated modulation of interaction between excitatory and inhibitory synaptic influences on smooth muscles. NEUROPHYSIOLOGY+ 2004. [DOI: 10.1007/s11062-005-0033-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Mechanisms of calcium signaling in smooth muscle cells explored with fluorescence confocal imaging. NEUROPHYSIOLOGY+ 2004. [DOI: 10.1007/s11062-005-0035-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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