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Bergh C, Heusser SA, Howard R, Lindahl E. Markov state models of proton- and pore-dependent activation in a pentameric ligand-gated ion channel. eLife 2021; 10:68369. [PMID: 34652272 PMCID: PMC8635979 DOI: 10.7554/elife.68369] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Accepted: 10/14/2021] [Indexed: 01/03/2023] Open
Abstract
Ligand-gated ion channels conduct currents in response to chemical stimuli, mediating electrochemical signaling in neurons and other excitable cells. For many channels, the details of gating remain unclear, partly due to limited structural data and simulation timescales. Here, we used enhanced sampling to simulate the pH-gated channel GLIC, and construct Markov state models (MSMs) of gating. Consistent with new functional recordings, we report in oocytes, our analysis revealed differential effects of protonation and mutation on free-energy wells. Clustering of closed- versus open-like states enabled estimation of open probabilities and transition rates, while higher-order clustering affirmed conformational trends in gating. Furthermore, our models uncovered state- and protonation-dependent symmetrization. This demonstrates the applicability of MSMs to map energetic and conformational transitions between ion-channel functional states, and how they reproduce shifts upon activation or mutation, with implications for modeling neuronal function and developing state-selective drugs.
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Affiliation(s)
- Cathrine Bergh
- Science for Life Laboratory and Swedish e-Science Research Center, Department of Applied Physics, KTH Royal Institute of Technology, Solna, Sweden
| | - Stephanie A Heusser
- Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Solna, Sweden
| | - Rebecca Howard
- Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Solna, Sweden
| | - Erik Lindahl
- Science for Life Laboratory and Swedish e-Science Research Center, Department of Applied Physics, KTH Royal Institute of Technology, Solna, Sweden.,Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Solna, Sweden
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2
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Fakhfouri G, Rahimian R, Dyhrfjeld-Johnsen J, Zirak MR, Beaulieu JM. 5-HT 3 Receptor Antagonists in Neurologic and Neuropsychiatric Disorders: The Iceberg Still Lies beneath the Surface. Pharmacol Rev 2019; 71:383-412. [PMID: 31243157 DOI: 10.1124/pr.118.015487] [Citation(s) in RCA: 58] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
5-HT3 receptor antagonists, first introduced to the market in the mid-1980s, are proven efficient agents to counteract chemotherapy-induced emesis. Nonetheless, recent investigations have shed light on unappreciated dimensions of this class of compounds in conditions with an immunoinflammatory component as well as in neurologic and psychiatric disorders. The promising findings from multiple studies have unveiled several beneficial effects of these compounds in multiple sclerosis, stroke, Alzheimer disease, and Parkinson disease. Reports continue to uncover important roles for 5-HT3 receptors in the physiopathology of neuropsychiatric disorders, including depression, anxiety, drug abuse, and schizophrenia. This review addresses the potential of 5-HT3 receptor antagonists in neurology- and neuropsychiatry-related disorders. The broad therapeutic window and high compliance observed with these agents position them as suitable prototypes for the development of novel pharmacotherapeutics with higher efficacy and fewer adverse effects.
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Affiliation(s)
- Gohar Fakhfouri
- Department of Psychiatry and Neuroscience, Faculty of Medicine, CERVO Brain Research Centre, Laval University, Quebec, Quebec, Canada (G.F., R.R.); Sensorion SA, Montpellier, France (J.D.-J.); Department of Pharmacodynamics and Toxicology, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran (M.R.Z.); and Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada (J.-M.B.)
| | - Reza Rahimian
- Department of Psychiatry and Neuroscience, Faculty of Medicine, CERVO Brain Research Centre, Laval University, Quebec, Quebec, Canada (G.F., R.R.); Sensorion SA, Montpellier, France (J.D.-J.); Department of Pharmacodynamics and Toxicology, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran (M.R.Z.); and Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada (J.-M.B.)
| | - Jonas Dyhrfjeld-Johnsen
- Department of Psychiatry and Neuroscience, Faculty of Medicine, CERVO Brain Research Centre, Laval University, Quebec, Quebec, Canada (G.F., R.R.); Sensorion SA, Montpellier, France (J.D.-J.); Department of Pharmacodynamics and Toxicology, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran (M.R.Z.); and Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada (J.-M.B.)
| | - Mohammad Reza Zirak
- Department of Psychiatry and Neuroscience, Faculty of Medicine, CERVO Brain Research Centre, Laval University, Quebec, Quebec, Canada (G.F., R.R.); Sensorion SA, Montpellier, France (J.D.-J.); Department of Pharmacodynamics and Toxicology, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran (M.R.Z.); and Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada (J.-M.B.)
| | - Jean-Martin Beaulieu
- Department of Psychiatry and Neuroscience, Faculty of Medicine, CERVO Brain Research Centre, Laval University, Quebec, Quebec, Canada (G.F., R.R.); Sensorion SA, Montpellier, France (J.D.-J.); Department of Pharmacodynamics and Toxicology, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran (M.R.Z.); and Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada (J.-M.B.)
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3
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Evidence for an effect of receptor density on ligand occupancy and agonist EC 50. Sci Rep 2019; 9:19111. [PMID: 31836743 PMCID: PMC6910986 DOI: 10.1038/s41598-019-55361-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2019] [Accepted: 11/21/2019] [Indexed: 01/16/2023] Open
Abstract
Drug-receptor interaction theory predicts that proportional receptor occupancy is a function of ligand concentration as defined by a ligand-receptor affinity constant, and is independent of receptor density. However, we previously observed that the EC50 of 5-HT reduced as the density of 5-HT3 receptors increased, suggesting an effect of receptor density on occupancy. The current study was designed to maximise variability in experimentally observed currents and confirm this apparent contradiction prospectively. Xenopus oocytes were injected with RNA encoding 5-HT3A receptors under conditions designed to achieve varying receptor expression levels and 5-HT-evoked currents measured using two electrode voltage clamp. Results from 99 oocytes showed that as the maximal peak current increased from 0.05 µA to 12.1 µA there was a 3.7-fold reduction in EC50. Since occupancy and conductance are directly related in this system, this indicates that for a given concentration of 5-HT, proportional occupancy increases with increased receptor density. We conclude that normalising data masks this correlation, and can result in reduced accuracy of pharmacological measurements. We propose a mechanistic explanation for our observations.
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Park YS, Sung KW. Selective serotonin reuptake inhibitor escitalopram inhibits 5-HT 3 receptor currents in NCB-20 cells. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2019; 23:509-517. [PMID: 31680773 PMCID: PMC6819908 DOI: 10.4196/kjpp.2019.23.6.509] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/06/2019] [Revised: 10/09/2019] [Accepted: 10/10/2019] [Indexed: 11/15/2022]
Abstract
Escitalopram is one of selective serotonin reuptake inhibitor antidepressants. As an S-enantiomer of citalopram, it shows better therapeutic outcome in depression and anxiety disorder treatment because it has higher selectivity for serotonin reuptake transporter than citalopram. The objective of this study was to determine the direct inhibitory effect of escitalopram on 5-hydroxytryptamine type 3 (5-HT3) receptor currents and study its blocking mechanism to explore additional pharmacological effects of escitalopram through 5-HT3 receptors. Using a whole-cell voltage clamp method, we recorded currents of 5-HT3 receptors when 5-HT was applied alone or co-applied with escitalopram in cultured NCB-20 neuroblastoma cells known to express 5-HT3 receptors. 5-HT induced currents were inhibited by escitalopram in a concentration-dependent manner. EC50 of 5-HT on 5-HT3 receptor currents was increased by escitalopram while the maximal peak amplitude was reduced by escitalopram. The inhibitory effect of escitalopram was voltage independent. Escitalopram worked more effectively when it was co-applied with 5-HT than pre-application of escitalopram. Moreover, escitalopram showed fast association and dissociation to the open state of 5-HT3 receptor channel with accelerating receptor desensitization. Although escitalopram accelerated 5-HT3 receptor desensitization, it did not change the time course of desensitization recovery. These results suggest that escitalopram can inhibit 5-HT3 receptor currents in a non-competitive manner with the mechanism of open channel blocking.
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Affiliation(s)
- Yong Soo Park
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul 06591, Korea
| | - Ki-Wug Sung
- Department of Pharmacology, College of Medicine, The Catholic University of Korea, Seoul 06591, Korea
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Park YS, Myeong SH, Kim IB, Sung KW. Tricyclic antidepressant amitriptyline inhibits 5-hydroxytryptamine 3 receptor currents in NCB-20 cells. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2018; 22:585-595. [PMID: 30181705 PMCID: PMC6115347 DOI: 10.4196/kjpp.2018.22.5.585] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Revised: 06/22/2018] [Accepted: 07/01/2018] [Indexed: 12/29/2022]
Abstract
Amitriptyline, a tricyclic antidepressant, is commonly used to treat depression and neuropathic pain, but its mechanism is still unclear. We tested the effect of amitriptyline on 5-hydroxytryptamine 3 (5-HT3) receptor currents and studied its blocking mechanism because the clinical applications of amitriptyline overlapped with 5-HT3 receptor therapeutic potentials. Using a whole-cell voltage clamp method, we recorded the currents of the 5-HT3 receptor when 5-HT was applied alone or co-applied with amitriptyline in cultured NCB-20 neuroblastoma cells known to express 5-HT3 receptors. To elucidate the mechanism of amitriptyline, we simulated the 5-HT3 receptor currents using Berkeley Madonna® software and calculated the rate constants of the agonist binding and receptor transition steps. The 5-HT3 receptor currents were inhibited by amitriptyline in a concentration-dependent, voltage-independent manner, and a competitive mode. Amitriptyline accelerated the desensitization of the 5-HT3 receptor. When amitriptyline was applied before 5-HT treatment, the currents rose slowly until the end of 5-HT treatment. When amitriptyline was co-applied with 5-HT, currents rose and decayed rapidly. Peak current amplitudes were decreased in both applications. All macroscopic currents recorded in whole cell voltage clamping experiments were reproduced by simulation and the changes of rate constants by amitriptyline were correlated with macroscopic current recording data. These results suggest that amitriptyline blocks the 5-HT3 receptor by close and open state blocking mechanisms, in a competitive manner. We could expand an understanding of pharmacological mechanisms of amitriptyline related to the modulation of a 5-HT3 receptor, a potential target of neurologic and psychiatric diseases through this study.
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Affiliation(s)
- Yong Soo Park
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul 06591, Korea
| | - Seok Ho Myeong
- Department of Pharmacology, College of Medicine, The Catholic University of Korea, Seoul 06591, Korea
| | - In-Beom Kim
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul 06591, Korea
| | - Ki-Wug Sung
- Department of Pharmacology, College of Medicine, The Catholic University of Korea, Seoul 06591, Korea
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6
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Sévoz-Couche C, Brouillard C. Key role of 5-HT 3 receptors in the nucleus tractus solitarii in cardiovagal stress reactivity. Neurosci Biobehav Rev 2016; 74:423-432. [PMID: 27131969 DOI: 10.1016/j.neubiorev.2016.04.014] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Revised: 04/18/2016] [Accepted: 04/20/2016] [Indexed: 01/01/2023]
Abstract
Serotonin plays a modulatory role in central control of the autonomic nervous system (ANS). The nucleus tractus solitarii (NTS) in the medulla is an area of viscerosomatic integration innervated by both central and peripheral serotonergic fibers. Influences from different origins therefore trigger the release of serotonin into the NTS and exert multiple influences on the ANS. This major influence on the ANS is also mediated by activation of several receptors in the NTS. In particular, the NTS is the central zone with the highest density of serotonin3 (5-HT3) receptors. In this review, we present evidence that 5-HT3 receptors in the NTS play a key role in one of the crucial homeostatic responses to acute and chronic stress: inhibitory modulation of the parasympathetic component of the ANS. The possible functional interactions of 5-HT3 receptors with GABAA and NK1 receptors in the NTS are also discussed.
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Affiliation(s)
- Caroline Sévoz-Couche
- Sorbonne Universités, UPMC Univ Paris 06, INSERM, UMRS1158 Neurophysiologie Respiratoire Expérimentale et Clinique, Paris, France.
| | - Charly Brouillard
- Sorbonne Universités, UPMC Univ Paris 06, INSERM, UMRS1158 Neurophysiologie Respiratoire Expérimentale et Clinique, Paris, France
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7
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Wu ZS, Cheng H, Jiang Y, Melcher K, Xu HE. Ion channels gated by acetylcholine and serotonin: structures, biology, and drug discovery. Acta Pharmacol Sin 2015; 36:895-907. [PMID: 26238288 PMCID: PMC4564887 DOI: 10.1038/aps.2015.66] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Accepted: 06/24/2015] [Indexed: 12/17/2022] Open
Abstract
The nicotinic acetylcholine receptors (nAChRs) and the 5-HT3 receptors (5-HT3Rs) are cation-selective members of the pentameric ligand-gated ion channels (pLGICs), which are oligomeric protein assemblies that convert a chemical signal into an ion flux through postsynaptic membrane. They are critical components for synaptic transmission in the nervous system, and their dysfunction contributes to many neurological disorders. The diverse subunit compositions of pLGICs give rise to complex mechanisms of ligand recognition, channel gating, and ion-selective permeability, which have been demonstrated in numerous electrophysiological and molecular biological studies, and unraveled by progress in studying the structural biology of this protein family. In this review, we discuss recent insights into the structural and functional basis of two cation-selective pLGICs, the nAChR and the 5-HT3R, including their subunit compositions, ligand binding, and channel gating mechanisms. We also discuss their relevant pharmacology and drug discovery for treating various neurological disorders. Finally, we review a model of two alternative ion conducting pathways based on the latest 5-HT3A crystal structure.
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Newman AS, Batis N, Grafton G, Caputo F, Brady CA, Lambert JJ, Peters JA, Gordon J, Brain KL, Powell AD, Barnes NM. 5-Chloroindole: a potent allosteric modulator of the 5-HT₃ receptor. Br J Pharmacol 2014; 169:1228-38. [PMID: 23594147 DOI: 10.1111/bph.12213] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Revised: 01/08/2013] [Accepted: 02/16/2013] [Indexed: 12/01/2022] Open
Abstract
BACKGROUND AND PURPOSE The 5-HT₃ receptor is a ligand-gated ion channel that is modulated allosterically by various compounds including colchicine, alcohols and volatile anaesthetics. However the positive allosteric modulators (PAMs) identified to date have low affinity, which hinders investigation because of non-selective effects at pharmacologically active concentrations. The present study identifies 5-chloroindole (Cl-indole) as a potent PAM of the 5-HT₃ receptor. EXPERIMENTAL APPROACH 5-HT₃ receptor function was assessed by the increase in intracellular calcium and single-cell electrophysiological recordings in HEK293 cells stably expressing the h5-HT₃A receptor and also the mouse native 5-HT₃ receptor that increases neuronal contraction of bladder smooth muscle. KEY RESULTS Cl-indole (1-100 μM) potentiated agonist (5-HT) and particularly partial agonist [(S)-zacopride, DDP733, RR210, quipazine, dopamine, 2-methyl-5-HT, SR57227A, meta chlorophenyl biguanide] induced h5-HT₃A receptor-mediated responses. This effect of Cl-indole was also apparent at the mouse native 5-HT₃ receptor. Radioligand-binding studies identified that Cl-indole induced a small (≈ twofold) increase in the apparent affinity of 5-HT for the h5-HT₃A receptor, whereas there was no effect upon the affinity of the antagonist, tropisetron. Cl-indole was able to reactivate desensitized 5-HT₃ receptors. In contrast to its effect on the 5-HT₃ receptor, Cl-indole did not alter human nicotinic α7 receptor responses. CONCLUSIONS AND IMPLICATIONS The present study identifies Cl-indole as a relatively potent and selective PAM of the 5-HT₃ receptor; such compounds will aid investigation of the molecular basis for allosteric modulation of the 5-HT₃ receptor and may assist the discovery of novel therapeutic drugs targeting this receptor.
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Affiliation(s)
- Amy S Newman
- Cellular and Molecular Neuropharmacology Research Group, Clinical and Experimental Medicine, Medical School, University of Birmingham, Edgbaston, Birmingham, UK
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Komal P, Gudavicius G, Nelson CJ, Nashmi R. T-cell receptor activation decreases excitability of cortical interneurons by inhibiting α7 nicotinic receptors. J Neurosci 2014; 34:22-35. [PMID: 24381265 PMCID: PMC6608162 DOI: 10.1523/jneurosci.2093-13.2014] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Revised: 11/04/2013] [Accepted: 11/07/2013] [Indexed: 11/21/2022] Open
Abstract
Many proteins in the immune system are also expressed in the brain. One such class of immune proteins are T-cell receptors (TCRs), whose functions in T lymphocytes in adaptive immunity are well characterized. In the brain, TCRs are confined to neocortical neurons, but their functional role has not been determined. In mouse layer 1 neocortical neurons, TCR activation inhibited α7 nicotinic currents. TCRs modulated α7 currents via tyrosine phosphorylation of α7 nicotinic receptors (nAChRs) through src tyrosine kinases because eliminating lck kinase expression, coexpressing fyn kinase dead, or mutating tyrosine to alanine in α7 blocked the effect of TCR activation. We found that TCR stimulation decreased surface α7 nAChRs and reduced single-channel conductance. These results reveal that TCRs play a major role in the modulation of cholinergic neurotransmission in the brain mediated by α7 nAChRs and that this has a profound effect on regulating neuronal excitability.
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Affiliation(s)
| | - Geoff Gudavicius
- Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, V8W 3N5, Canada
| | - Christopher J. Nelson
- Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, V8W 3N5, Canada
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The Role of Neurotransmitters in Protection against Amyloid- β Toxicity by KiSS-1 Overexpression in SH-SY5Y Neurons. ISRN NEUROSCIENCE 2013; 2013:253210. [PMID: 24967306 PMCID: PMC4045539 DOI: 10.1155/2013/253210] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Accepted: 06/19/2013] [Indexed: 12/21/2022]
Abstract
Recent studies have suggested that the kisspeptin (KP) and kissorphin (KSO) peptides have neuroprotective actions against the Alzheimer's amyloid-β (Aβ) peptide. Overexpression of the human KiSS-1 gene that codes for KP and KSO peptides in SH-SY5Y neurons has also been shown to inhibit Aβ neurotoxicity. The in vivo actions of KP include activation of neuroendocrine and neurotransmitter systems. The present study used antagonists of KP, neuropeptide FF (NPFF), opioids, oxytocin, estrogen, adrenergic, cholinergic, dopaminergic, serotonergic, and γ-aminobutyric acid (GABA) receptors plus inhibitors of catalase, cyclooxygenase, nitric oxide synthase, and the mitogen activated protein kinase cascade to characterize the KiSS-1 gene overexpression neuroprotection against Aβ cell model. The results showed that KiSS-1 overexpression is neuroprotective against Aβ and the action appears to involve the KP or KSO peptide products of KiSS-1 processing. The mechanism of neuroprotection does not involve the activation of the KP or NPFF receptors. Opioids play a role in the toxicity of Aβ in the KiSS-1 overexpression system and opioid antagonists naloxone or naltrexone inhibited Aβ toxicity. The mechanism of KiSS-1 overexpression induced protection against Aβ appears to have an oxytocin plus a cyclooxygenase dependent component, with the oxytocin antagonist atosiban and the cyclooxygenase inhibitor SC-560 both enhancing the toxicity of Aβ.
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Baptista-Hon DT, Deeb TZ, Lambert JJ, Peters JA, Hales TG. The minimum M3-M4 loop length of neurotransmitter-activated pentameric receptors is critical for the structural integrity of cytoplasmic portals. J Biol Chem 2013; 288:21558-68. [PMID: 23740249 DOI: 10.1074/jbc.m113.481689] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 5-HT3A receptor homology model, based on the partial structure of the nicotinic acetylcholine receptor from Torpedo marmorata, reveals an asymmetric ion channel with five portals framed by adjacent helical amphipathic (HA) stretches within the 114-residue loop between the M3 and M4 membrane-spanning domains. The positive charge of Arg-436, located within the HA stretch, is a rate-limiting determinant of single channel conductance (γ). Further analysis reveals that positive charge and volume of residue 436 are determinants of 5-HT3A receptor inward rectification, exposing an additional role for portals. A structurally unresolved stretch of 85 residues constitutes the bulk of the M3-M4 loop, leaving a >45-Å gap in the model between M3 and the HA stretch. There are no additional structural data for this loop, which is vestigial in bacterial pentameric ligand-gated ion channels and was largely removed for crystallization of the Caenorhabditis elegans glutamate-activated pentameric ligand-gated ion channels. We created 5-HT3A subunit loop truncation mutants, in which sequences framing the putative portals were retained, to determine the minimum number of residues required to maintain their functional integrity. Truncation to between 90 and 75 amino acids produced 5-HT3A receptors with unaltered rectification. Truncation to 70 residues abolished rectification and increased γ. These findings reveal a critical M3-M4 loop length required for functions attributable to cytoplasmic portals. Examination of all 44 subunits of the human neurotransmitter-activated Cys-loop receptors reveals that, despite considerable variability in their sequences and lengths, all M3-M4 loops exceed 70 residues, suggesting a fundamental requirement for portal integrity.
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Affiliation(s)
- Daniel T Baptista-Hon
- Institute of Academic Anaesthesia, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
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12
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Li QZ, Cho HS, Jeun SH, Kim KJ, Choi SJ, Sung KW. Effects of grape seed proanthocyanidin on 5-hydroxytryptamine(3) receptors in NCB-20 neuroblastoma cells. Biol Pharm Bull 2011; 34:1109-15. [PMID: 21720021 DOI: 10.1248/bpb.34.1109] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Proanthocyanidin is a phenolic compound present in plants, that has antioxidant, antinociceptive, anti-emetic, and neuroprotective properties. We investigated the actions of proanthocyanidin from grape seeds on 5-hydroxytryptamine (5-HT)(3) receptors in NCB-20 neuroblastoma cells using a whole-cell voltage clamp technique. Co-treatment of proanthocyanidin (0.3-100 µg/ml) and 3 µM 5-HT (near EC(50)) produced a slight inhibition of 5-HT-induced inward peak current (I(5-HT)) in NCB-20 cells, but pretreatment with proanthocyanidin for 30 s before application of 5-HT induced a much larger inhibition of I(5-HT) in an irreversible, concentration- and time-dependent manner (IC(50)=6.5±0.4 µg/ml, Hill coefficient=2.5±0.1). Proanthocyanidin also produced a concentration-dependent inhibition of currents induced by 30 µM 5-HT, near-maximal concentration (IC(50)=22.1±0.4 µg/ml, Hill coefficient=2.4±0.1). High concentrations (≧30 µg/ml) of proanthocyanidin caused a concentration-dependent inhibition of the activation and desensitization of currents induced by 30 µM 5-HT. Further studies showed that pretreatment of 20 µg/ml proanthocyanidin caused not only a rightward shift of the dose-response curve for 5-HT (EC(50) shift from 2.7±0.4 to 6.2±0.5 µM), but also a decreased E(max) (inhibition by 37.5±1.3%). The proanthocyanidin-induced inhibition of 5-HT(3) receptors did not show a significant difference within the testing holding potential ranges (-50-+30 mV). These results suggest that proanthocyanidin inhibits 5-HT(3) receptor function in NCB-20 cells in a noncompetitive mode, and that this inhibitory effect of proanthocyanidin probably contributes to the pharmacological actions of proanthocyanidin.
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Affiliation(s)
- Qing-Zhong Li
- Department of Pharmacology, The Catholic University of Korea, 505 Banpo-dong, Seocho-gu, Seoul 137–701, Korea
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13
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Abstract
Cys-loop receptors are membrane-spanning neurotransmitter-gated ion channels that are responsible for fast excitatory and inhibitory transmission in the peripheral and central nervous systems. The best studied members of the Cys-loop family are nACh, 5-HT3, GABAA and glycine receptors. All these receptors share a common structure of five subunits, pseudo-symmetrically arranged to form a rosette with a central ion-conducting pore. Some are cation selective (e.g. nACh and 5-HT3) and some are anion selective (e.g. GABAA and glycine). Each receptor has an extracellular domain (ECD) that contains the ligand-binding sites, a transmembrane domain (TMD) that allows ions to pass across the membrane, and an intracellular domain (ICD) that plays a role in channel conductance and receptor modulation. Cys-loop receptors are the targets for many currently used clinically relevant drugs (e.g. benzodiazepines and anaesthetics). Understanding the molecular mechanisms of these receptors could therefore provide the catalyst for further development in this field, as well as promoting the development of experimental techniques for other areas of neuroscience.In this review, we present our current understanding of Cys-loop receptor structure and function. The ECD has been extensively studied. Research in this area has been stimulated in recent years by the publication of high-resolution structures of nACh receptors and related proteins, which have permitted the creation of many Cys loop receptor homology models of this region. Here, using the 5-HT3 receptor as a typical member of the family, we describe how homology modelling and ligand docking can provide useful but not definitive information about ligand interactions. We briefly consider some of the many Cys-loop receptors modulators. We discuss the current understanding of the structure of the TMD, and how this links to the ECD to allow channel gating, and consider the roles of the ICD, whose structure is poorly understood. We also describe some of the current methods that are beginning to reveal the differences between different receptor states, and may ultimately show structural details of transitions between them.
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Sanghvi M, Hamouda AK, Davis MI, Morton RA, Srivastava S, Pandhare A, Duddempudi PK, Machu TK, Lovinger DM, Cohen JB, Blanton MP. Hydrophobic photolabeling studies identify the lipid-protein interface of the 5-HT3A receptor. Biochemistry 2009; 48:9278-86. [PMID: 19715355 DOI: 10.1021/bi901208j] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
A HEK-293 cell line that stably expresses mouse 5-HT(3A)Rs containing a C-terminal extension that confers high-affinity binding of alpha-bungarotoxin (alphaBgTx) was established (alphaBgTx-5-HT(3A)Rs) and used to purify alphaBgTx-5-HT(3A)Rs in a lipid environment for use in structural studies using photoaffinity labeling. alphaBgTx-5-HT(3A)Rs were expressed robustly (60 pmol of [(3)H]BRL-43694 binding sites (approximately 3 microg of receptor) per milligram of protein) and displayed the same functional properties as wild-type receptors (serotonin EC(50) = 5.3 +/- 0.04 microM). While [(125)I]alphaBgTx bound to the alphaBgTx-5-HT(3A)Rs with high affinity (K(d) = 11 nM), application of nonradioactive alphaBgTx (up to 300 microM) had no effect on serotonin-induced current responses. alphaBgTx-5-HT(3A)Rs were purified on an alphaBgTx-derivatized affinity column from detergent extracts in milligram quantities and at approximately 25% purity. The hydrophobic photolabel 3-trifluoromethyl-3-(m-[(125)I]iodophenyl)diazirine ([(125)I]TID) was used to identify the amino acids at the lipid-protein interface of purified and lipid-reconstituted alphaBgTx-5-HT(3A)Rs. [(125)I]TID photoincorporation into the alphaBgTx-5-HT(3A)R subunit was initially mapped to subunit proteolytic fragments of 8 kDa, containing the M4 transmembrane segment and approximately 60% of incorporated (125)I, and 17 kDa, containing the M1-M3 transmembrane segments. Within the M4 segment, [(125)I]TID labeled Ser(451), equivalent to the [(125)I]TID-labeled residue Thr(422) at the lipid-exposed face of the Torpedo nicotinic acetylcholine receptor (nAChR) alpha1M4 alpha-helix. These results provide a first definition of the surface of the 5-HT(3A)R M4 helix that is exposed to lipid and establish that this surface is equivalent to the surface exposed to lipid in the Torpedo nAChR.
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Affiliation(s)
- Mitesh Sanghvi
- Department of Pharmacology and Neuroscience and Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA
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15
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3B but which 3B and that's just one of the questions: the heterogeneity of human 5-HT3 receptors. Trends Pharmacol Sci 2009; 29:437-44. [PMID: 18597859 DOI: 10.1016/j.tips.2008.06.001] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Revised: 04/14/2008] [Accepted: 06/15/2008] [Indexed: 01/19/2023]
Abstract
The 5-hydroxytryptamine 3 (5-HT3) receptor is expressed widely in the central and peripheral nervous systems, where it mediates or modulates a wide range of physiological processes. The receptor is targeted by drugs administered for nausea and/or emesis and irritable bowel syndrome and has been proposed as a potential drug target in various psychiatric disorders. The 5-HT3 receptor is a pentameric ligand-gated ion channel and belongs to the Cys-loop receptor family. In contrast to the immense heterogeneity characterizing other Cysloop receptors, native 5-HT3 receptors historically have been considered a much more homogenous receptor population. However, the recent discovery of additional 5-HT3 subunits and the dawning realization that central and peripheral 5-HT3 receptor populations might comprise several subtypes characterized by distinct functional properties has emphasized the complexity of human 5-HT3 receptor signaling. In this review potential implications of these findings and of the entirely new layer of interindividual diversity introduced to the 5-HT3 receptor system by genetic variations will be outlined.
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16
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Drisdel RC, Sharp D, Henderson T, Hales TG, Green WN. High affinity binding of epibatidine to serotonin type 3 receptors. J Biol Chem 2008; 283:9659-65. [PMID: 17702741 PMCID: PMC2442297 DOI: 10.1074/jbc.m703672200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2007] [Revised: 08/15/2007] [Indexed: 01/22/2023] Open
Abstract
Epibatidine and mecamylamine are ligands used widely in the study of nicotinic acetylcholine receptors (nAChRs) in the central and peripheral nervous systems. In the present study, we find that nicotine blocks only 75% of (125)I-epibatidine binding to rat brain membranes, whereas ligands specific for serotonin type 3 receptors (5-HT(3)Rs) block the remaining 25%. (125)I-Epibatidine binds with a high affinity to native 5-HT(3)Rs of N1E-115 cells and to receptors composed of only 5-HT(3A) subunits expressed in HEK cells. In these cells, serotonin, the 5-HT(3)R-specific antagonist MDL72222, and the 5-HT(3)R agonist chlorophenylbiguanide readily competed with (125)I-epibatidine binding to 5-HT(3)Rs. Nicotine was a poor competitor for (125)I-epibatidine binding to 5-HT(3)Rs. However, the noncompetitive nAChR antagonist mecamylamine acted as a potent competitive inhibitor of (125)I-epibatidine binding to 5-HT(3)Rs. Epibatidine inhibited serotonin-induced currents mediated by endogenous 5-HT(3)Rs in neuroblastoma cell lines and 5-HT(3A)Rs expressed in HEK cells in a competitive manner. Our results demonstrate that 5-HT(3)Rs are previously uncharacterized high affinity epibatidine binding sites in the brain and indicate that epibatidine and mecamylamine act as 5-HT(3)R antagonists. Previous studies that depended on epibatidine and mecamylamine as nAChR-specific ligands, in particular studies of analgesic properties of epibatidine, may need to be reinterpreted with respect to the potential role of 5-HT(3)Rs.
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Affiliation(s)
- Renaldo C Drisdel
- Department of Neurobiology, University of Chicago, Chicago, IL 60637, USA
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17
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Chameau P, van Hooft JA. Serotonin 5-HT3 receptors in the central nervous system. Cell Tissue Res 2006; 326:573-81. [PMID: 16826372 DOI: 10.1007/s00441-006-0255-8] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2006] [Accepted: 05/19/2006] [Indexed: 12/20/2022]
Abstract
The 5-HT(3) receptor is a ligand-gated ion channel activated by serotonin (5-HT). Although originally identified in the peripheral nervous system, the 5-HT(3) receptor is also ubiquitously expressed in the central nervous system. Sites of expression include several brain stem nuclei and higher cortical areas such as the amygdala, hippocampus, and cortex. On the subcellular level, both presynaptic and postsynaptic 5-HT(3) receptors can be found. Presynaptic 5-HT(3) receptors are involved in mediating or modulating neurotransmitter release. Postsynaptic 5-HT(3) receptors are preferentially expressed on interneurons. In view of this specific expression pattern and of the well-established role of 5-HT as a neurotransmitter shaping development, we speculate that 5-HT(3) receptors play a role in the formation and function of cortical circuits.
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Affiliation(s)
- Pascal Chameau
- Swammerdam Institute for Life Sciences, Center for NeuroScience, University of Amsterdam, P.O. Box 94084, NL-1090 GB, Amsterdam, The Netherlands
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18
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Lacolley PJ, Owen JR, Bates JN, Johnson AK, Lewis SJ. Tachyphylaxis to 5-HT3-receptor-mediated activation of vagal afferents is prevented by co-activation of 5-HT2 receptors. Brain Res 2006; 1093:105-15. [PMID: 16712808 DOI: 10.1016/j.brainres.2006.03.090] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2005] [Revised: 03/18/2006] [Accepted: 03/22/2006] [Indexed: 11/24/2022]
Abstract
Functional studies have provided evidence that 5-HT(3) ion-channel receptors (5-HT(3)Rs) on vagal cardiopulmonary afferents mediating the Bezold-Jarisch reflex (BJR) rapidly desensitize upon repeated exposure to selective 5-HT(3)R agonists. G-protein-coupled 5-HT(2) receptors (5-HT(2)Rs) also exist on vagal afferents, although activation of these receptors does not elicit the BJR. However, there is in vivo evidence that 5-HT(2)Rs may regulate the activity of 5-HT(3)Rs. The aim of this study was to determine whether co-activation of 5-HT(2)Rs prevents desensitization of 5-HT(3)Rs mediating the BJR in conscious rats. The principal findings were that (1) tachyphylaxis rapidly developed to the BJR-mediated hemodynamic responses elicited by successive injections of 5-HT(3)R agonists and (2) co-injection of the selective 5-HT(2)R agonist, alpha-methyl-5-HT, prevented tachyphylaxis to the BJR-mediated hemodynamic responses elicited by the 5-HT(3)R agonists. Additional studies provided evidence that (1) tachyphylaxis to the 5-HT(3)R agonists was not due to impairment of the central or efferent processing of the BJR, and (2) the pressor responses elicited by alpha-methyl-5-HT were not responsible for preventing tachyphylaxis to the BJR reflex responses elicited by 5-HT(3)R agonists. These results suggest that the loss of response to 5-HT(3)R agonists is due to desensitization of 5-HT(3)Rs on vagal afferents mediating the BJR and that co-activation of 5-HT(2)Rs prevents the desensitization of these 5-HT(3)Rs.
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MESH Headings
- Animals
- Hemodynamics/drug effects
- Hemodynamics/physiology
- Male
- Neurons, Afferent/drug effects
- Neurons, Afferent/metabolism
- Rats
- Rats, Sprague-Dawley
- Receptors, Serotonin, 5-HT2/drug effects
- Receptors, Serotonin, 5-HT2/metabolism
- Receptors, Serotonin, 5-HT3/drug effects
- Receptors, Serotonin, 5-HT3/metabolism
- Reflex/drug effects
- Reflex/physiology
- Serotonin Receptor Agonists/pharmacology
- Tachyphylaxis/physiology
- Vagus Nerve/drug effects
- Vagus Nerve/metabolism
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Affiliation(s)
- Patrick J Lacolley
- Department of Pharmacology, University of Iowa, Iowa City, IA 52242, USA.
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19
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Hodge CW, Kelley SP, Bratt AM, Iller K, Schroeder JP, Besheer J. 5-HT(3A) receptor subunit is required for 5-HT3 antagonist-induced reductions in alcohol drinking. Neuropsychopharmacology 2004; 29:1807-13. [PMID: 15162158 DOI: 10.1038/sj.npp.1300498] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The ionotropic serotonin subtype-3 (5-HT3) receptor has emerged as a potential therapeutic target in the treatment of alcohol abuse and alcoholism because selective pharmacological antagonists reduce alcohol consumption in preclinical and clinical models. 5-HT binds to the extracellular N-terminus of the 5-HT(3A) receptor subunit but receptor activation is also enhanced by distinct allosteric sites, which indicates the presence of other receptor subunits. It is not known if specific molecular subunits of the 5-HT3 receptor modulate alcohol drinking. To address this issue, we characterized acute locomotor response to alcohol and alcohol consumption in a two-bottle home-cage procedure by congenic C57BL/6J mice with a targeted deletion of the 5-HT(3A) receptor subunit gene. 5-HT(3A)-null mice did not differ from wild-type littermate controls on measures of spontaneous locomotor activity, habituation to a novel environment, or locomotor response to ethanol (0, 0.5, 1, or 2 g/kg). Moreover, null mice did not differ from controls on measures of ethanol (2-10%) intake and preference during or after a two-bottle home-cage sucrose fading procedure. Systemic administration of the 5-HT3 antagonist LY-278,584 (0-10 mg/kg) decreased intake of both sweetened (2% sucrose+10% ethanol) and unsweetened (10% ethanol) ethanol in wild-type mice only. These findings indicate that reduction of alcohol drinking produced by 5-HT3 antagonism is dependent on the presence of 5-HT(3A)-containing receptors.
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Affiliation(s)
- Clyde W Hodge
- Department of Psychiatry and Bowles Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
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20
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Krivoshein AV, Hess GP. Mechanism-Based Approach to the Successful Prevention of Cocaine Inhibition of the Neuronal (α3β4) Nicotinic Acetylcholine Receptor. Biochemistry 2003; 43:481-9. [PMID: 14717603 DOI: 10.1021/bi034838l] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The nicotinic acetylcholine receptor (nAChR) belongs to a family of five channel-forming proteins that regulate communication between the approximately 10(12) cells of the nervous system. A minimum mechanism of inhibition of the muscle-type nAChR (1) by the noncompetitive inhibitors cocaine and MK-801 [(+)-dizocilpine, an anticonvulsant] indicated they bind to a regulatory site, with higher affinity for the closed-channel form than for the open-channel form, thus shifting the equilibrium toward the closed-channel form and inhibiting receptor function. The mechanism predicts that compounds that bind to this regulatory site with equal or higher affinity for the open-channel conformation than for the closed-channel conformation will prevent receptor inhibition (1). Does a neuronal form of the receptor behave similarly? The mechanism of inhibition of the neuronal nAChR by cocaine and MK-801 using rapid chemical kinetic techniques was investigated. The alpha3beta4 nAChR stably expressed in HEK 293 cells was used in these investigations. Whole-cell currents originated from a major and minor nAChR isoform. Only the major isoform has been characterized. For the dominant, rapidly desensitizing isoform, the carbamoylcholine dissociation constant for the site controlling receptor activation, Kd, is 2 mM; the channel-opening equilibrium constant, Phi(-1), is 4; and the dominant desensitization rate constant, k34, is 20 s(-1). Cocaine inhibits the receptor noncompetitively, with an apparent KI of 84 and 26 microM at high and low carbamoylcholine concentrations, at which concentrations the receptor is mainly in the open- or closed-channel form, respectively. Similar results were obtained with MK-801. A combinatorially synthesized RNA ligand and a cocaine analogue alleviated cocaine inhibition of this neuronal receptor.
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Affiliation(s)
- Arcadius V Krivoshein
- Department of Molecular Biology and Genetics, 216 Biotechnology Building, Cornell University, Ithaca, New York 14853-2703, USA
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21
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Van Hooft JA, Wadman WJ. Ca2+ ions block and permeate serotonin 5-HT3 receptor channels in rat hippocampal interneurons. J Neurophysiol 2003; 89:1864-9. [PMID: 12611954 DOI: 10.1152/jn.00948.2002] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The serotonin 5-HT(3) receptor native to rat hippocampal CA1 stratum radiatum interneurons is blocked by Ca(2+) ions in a dose- and voltage-dependent manner, which is reflected by a region of negative slope conductance in the I-V curve. The steep dependence on the extracellular Ca(2+) concentration suggests that the channel contains more than one binding site for Ca(2+). A three barrier-two site model, based on Eyring rate theory, was used to describe the I-V curves. When extra- and intracellular K(+) and Cs(+) were substituted with Na(+), the I-V curves were accurately fit by the model, unlike the I-V curves recorded under standard ionic conditions. This suggests that the K(+) and Cs(+) permeabilities are small compared with that of Na(+). The distribution of the energy barriers and binding sites for Ca(2+) and Na(+) showed that the binding sites are located at approximately the 13' and the -4' position in the ion channel. The model predicts that at large hyperpolarized membrane potentials (more negative than -120 mV), the fractional Ca(2+) current amounts to approximately 1% of the total ion current. However, at physiologically relevant membrane potentials, the fractional Ca(2+) current is smaller (<0.1%) and the relative Ca(2+) permeability (P(Ca)/P(Na)) is estimated to be 0.10 at -60 mV.
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Affiliation(s)
- Johannes A Van Hooft
- University of Amsterdam, Swammerdam Institute for Life Sciences, Section Neurobiology, NL-1090 GB Amsterdam, The Netherlands.
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22
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Kelley SP, Bratt AM, Hodge CW. Targeted gene deletion of the 5-HT3A receptor subunit produces an anxiolytic phenotype in mice. Eur J Pharmacol 2003; 461:19-25. [PMID: 12568911 DOI: 10.1016/s0014-2999(02)02960-6] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Anxiety disorders are the most common psychiatric disorders. Typical medications used to treat patients are benzodiazepines or antidepressants that target serotonin (5-HT) activity. The ionotropic 5-HT(3) receptor has emerged as a potential therapeutic target because selective antagonist compounds reduce anxiety in rodents, primates, and humans. 5-HT binds to the extracellular N-terminus of the 5-HT(3A) receptor subunit, but receptor activation is also enhanced by distinct allosteric sites. It is not known if specific molecular subunits of the 5-HT(3) receptor modulate anxiety. To address this issue, we characterized anxiety-like behavior of mice with a targeted deletion of the 5-HT(3A) receptor subunit gene in the light/dark box, elevated plus maze, and novelty interaction animal models of anxiety. 5-HT(3A) null mice exhibited an anxiolytic behavioral phenotype that was highly correlated across behavioral measures. This evidence indicates that the 5-HT(3A) molecular subunit influences anxiety-like behavior. Pharmacotherapy that targets specifically the 5-HT(3A) receptor subunit may provide a novel treatment for anxiety disorders.
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Affiliation(s)
- Stephen P Kelley
- Ernest Gallo Clinic and Research Center, Department of Neurology, University of California at San Francisco, Emeryville, CA 94608, USA
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23
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Emerit MB, Doucet E, Darmon M, Hamon M. Native and cloned 5-HT(3A)(S) receptors are anchored to F-actin in clonal cells and neurons. Mol Cell Neurosci 2002; 20:110-24. [PMID: 12056843 DOI: 10.1006/mcne.2002.1133] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Using selective antibodies to visualize the short isoform of the 5-HT(3A) receptor, we report here that both native and cloned 5-HT(3A)(S) receptors formed clusters associated with F-actin in all cell types studied. NG 108-15 cells expressing native 5-HT(3A)(S) receptors, COS-7 cells transiently expressing 5-HT(3A)(S) subunits, and CHO cells stably transfected with a plasmid encoding the 5-HT(3A)(S) sequence all exhibited similar surface receptor topology with 5-HT(3A)(S) receptor cluster accumulation in F-actin-rich lamellipodia and microspikes. Colocalization and coclustering of 5-HT(3A)(S) subunits and F-actin were also observed in transfected hippocampal neurons. Treatment of the neurons with latrunculin-A, a compound altering F-actin polymerization, demonstrated that 5-HT(3A)(S) receptor cluster size and topology were dependent on F-actin integrity. These results suggest that the anchoring of 5-HT(3A)(S) receptor clusters to the cytoskeletal network probably plays a key role in the physiological regulation of the receptor topology and dynamics, as is the case for other members of the 4-TMD ion channel receptor family.
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Affiliation(s)
- Michel B Emerit
- INSERM U288, Neuropsychopharmacologie Moléculaire, Cellulaire et Fonctionnelle, C.H.U. Pitié-Salpêtrière, 91 Bd de l'Hôpital, 75634 Paris Cedex 13, France.
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24
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Bush TG, Spencer NJ, Watters N, Sanders KM, Smith TK. Effects of alosetron on spontaneous migrating motor complexes in murine small and large bowel in vitro. Am J Physiol Gastrointest Liver Physiol 2001; 281:G974-83. [PMID: 11557518 DOI: 10.1152/ajpgi.2001.281.4.g974] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Alosetron (Lotronex) is a serotonin subtype 3 (5-HT3) receptor antagonist that alleviates symptoms of irritable bowel syndrome (IBS) in female patients. Alosetron may act centrally, involve the alteration of ascending pain sensation, or modulate peristaltic, secretory, or sensory function. To investigate further the mechanisms underlying its action and gender selectivity we recorded the effect of increasing concentrations of alosetron or ondansetron on spontaneous migrating motor complexes (MMCs) from isolated terminal ileum or colon from C57BL/6 mice. Both antagonists inhibited MMC frequency before affects on duration or amplitude. The threshold of inhibition for alosetron was 100-fold less in small intestine from females (20 nM) than from males. The opposite effect of gender was observed with ondansetron in the colon. All MMCs were abolished by either drug at 10 microM. Our results demonstrate that alosetron selectively inhibits MMC frequency in isolated preparations of murine bowel. Because contractile events in the ileum correlate with symptoms of IBS in humans, the gender selectivity of alosetron may be caused by a direct action within the small intestine.
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Affiliation(s)
- T G Bush
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557-0046, USA
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25
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Fu XW, Wang D, Pan J, Farragher SM, Wong V, Cutz E. Neuroepithelial bodies in mammalian lung express functional serotonin type 3 receptor. Am J Physiol Lung Cell Mol Physiol 2001; 281:L931-40. [PMID: 11557597 DOI: 10.1152/ajplung.2001.281.4.l931] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Serotonin (5-HT) type 3 receptor (5-HT(3)-R) is a ligand-gated ion channel found primarily in the central and peripheral nervous system. We report expression and functional characterization of 5-HT(3)-R in pulmonary neuroepithelial body (NEB) cells. Using nonisotopic in situ hybridization, we demonstrate expression of 5-HT(3)-R mRNA in NEB cells in the lungs of different mammals (hamster, rabbit, mouse, and human). Dual immunocytochemistry (for 5-HT and 5-HT(3)-R) and confocal microscopy localized 5-HT(3)-R on NEB cell plasma membrane from rabbit. The electrophysiological characteristics of 5-HT(3)-R in NEB cells were studied in fresh slices of neonatal hamster lung using the whole cell patch-clamp technique. Application of the 5-HT (5-150 microM) and 5-HT(3)-R agonist 2-methyl-5-HT (5-150 microM) induced inward currents in a concentration-dependent manner. The 5-HT-induced current was blocked (76.5 +/- 5.9%) by the specific 5-HT(3)-R antagonist ICS-205-930 (50 microM), whereas katanserin and p-4-iodo-N-(2-[4-(methoxyphenyl)-1-piperazinyl]ethyl)-N-2-pyridinylbenzamide had minimal effects. Forskolin had no effect on desensitization and amplitude of the 5-HT-induced current. The reduction of Ca(2+) and Mg(2+) in the extracellular solution enhanced the amplitude of the 5-HT-induced current because of slower desensitization. Our studies suggest that 5-HT(3)-R in NEB cells may function as an autoreceptor and may potentially be involved in modulation of hypoxia signaling.
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Affiliation(s)
- X W Fu
- Division of Pathology, Department of Pediatric Laboratory Medicine, The Research Institute, The Hospital for Sick Children and University of Toronto, Toronto, Ontario, Canada M5G 1X8
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26
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Gunthorpe MJ, Lummis SC. Conversion of the ion selectivity of the 5-HT(3a) receptor from cationic to anionic reveals a conserved feature of the ligand-gated ion channel superfamily. J Biol Chem 2001; 276:10977-83. [PMID: 11139582 DOI: 10.1074/jbc.m009575200] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 5-hydroxytryptamine(3) (5-HT(3)) receptor is a member of a superfamily of ligand-gated ion channels, which includes nicotinic acetylcholine, gamma-aminobutyric acid, and glycine receptors. The receptors are either cation or anion selective, leading to their distinctive involvement in either excitatory or inhibitory neurotransmission. Using a combination of site-directed mutagenesis and electrophysiological characterization of homomeric 5-HT(3A) receptors expressed in HEK293 cells, we have identified a set of mutations that convert the ion selectivity of the 5-HT(3A) receptor from cationic to anionic; these were substitution of V13'T in M2 together with neutralization of glutamate residues (E-1'A) and the adjacent insertion of a proline residue (P-1') in the M1-M2 loop. Mutant receptors showed significant chloride permeability (P(Cl)/P(Na) = 12.3, P(Na)/P(Cl) = 0.08), whereas WT receptors are predominantly permeable to sodium (P(Na)/P(Cl) > 20, P(Cl)/P(Na) < 0.05). Since the equivalent mutations have previously been shown to convert alpha7 nicotinic acetylcholine receptors from cationic to anionic (Galzi J.-L., Devillers-Thiery, A, Hussy, N., Bertrand, S. Changeux, J. P., and Bertrand, D. (1992) Nature 359, 500-505) and, recently, the converse mutations have allowed the construction of a cation selective glycine receptor (Keramidas, A., Moorhouse, A. J., French, C. R., Schofield, P. R., and Barry, P. H. (2000) Biophys. J. 78, 247-259), it appears that the determinants of ion selectivity represent a conserved feature of the ligand-gated ion channel superfamily.
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Affiliation(s)
- M J Gunthorpe
- Division of Neurobiology, Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom
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27
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Sung KW, Engel SR, Allan AM, Lovinger DM. 5-HT(3) receptor function and potentiation by alcohols in frontal cortex neurons from transgenic mice overexpressing the receptor. Neuropharmacology 2000; 39:2346-51. [PMID: 10974318 DOI: 10.1016/s0028-3908(00)00064-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The function of 5-hydroxytryptamine (5-HT)(3) receptors was examined by whole-cell patch-clamp recording in dissociated frontal cortex neurons from 5-HT(3) receptor overexpressing transgenic, and wild-type mice. The effect of acute exposure to alcohols on the 5-HT(3) receptor-mediated ion current was also investigated. The 5-HT(3) receptors expressed on frontal cortex neurons in transgenic mice were activated by 5-HT and a selective 5-HT(3) receptor agonist, 2-methyl-5-HT. This current was blocked by zacopride, a specific 5-HT(3) receptor antagonist. Dissociated frontal cortex neurons from wild-type mice exhibited little or no 5-HT(3) receptor-mediated current. Ethanol (EtOH) and trichloroethanol (TCEt) potentiated the function of 5-HT(3) receptors overexpressed in transgenic mice. This is the first evidence that 5-HT(3) receptors exhibit sensitivity to alcohols when expressed by a central neuron.
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Affiliation(s)
- K W Sung
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 702 Light Hall, Nashville, TN 37232-0615, USA
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28
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Whalen EJ, Johnson AK, Lewis SJ. Functional evidence for the rapid desensitization of 5-HT(3) receptors on vagal afferents mediating the Bezold-Jarisch reflex. Brain Res 2000; 873:302-5. [PMID: 10930559 DOI: 10.1016/s0006-8993(00)02526-9] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The aim of this study was to determine whether 5-hydroxytryptamine (5-HT)(3) receptors on cardiopulmonary afferents mediating the Bezold-Jarisch reflex (BJR) desensitize upon repeated exposure to selective agonists. BJR-mediated falls in heart rate, diastolic arterial blood pressure and cardiac output elicited by the 5-HT(3)-receptor agonists, phenylbiguanide (100 microg/kg, i.v.) or 2-methyl-5-HT (100 microg/kg, i.v.), progressively diminished upon repeated injection in conscious rats. The BJR responses elicited by 5-HT (40 microg/kg, i.v.) were markedly reduced in rats which had received the above injections of phenylbiguanide or 2-methyl-5-HT whereas the BJR responses elicited by L-S-nitrosocysteine (10 micromol/kg, i.v.) were similar before and after the injections of the 5-HT(3) receptor agonists. These findings suggest that tachyphylaxis to 5-HT(3) receptor agonists may be due to the desensitization of 5-HT(3) receptors on cardiopulmonary afferents rather than the impairment of the central or peripheral processing of the BJR.
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Affiliation(s)
- E J Whalen
- Department of Pharmacology, The University of Iowa, Iowa City, IA 52242, USA
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29
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Hanna MC, Davies PA, Hales TG, Kirkness EF. Evidence for expression of heteromeric serotonin 5-HT(3) receptors in rodents. J Neurochem 2000; 75:240-7. [PMID: 10854267 DOI: 10.1046/j.1471-4159.2000.0750240.x] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The gene and cDNAs that encode a novel subunit of rodent serotonin 5-HT(3) receptors were isolated from mouse and rat tissues. Each of the new rodent subunits shares 40% amino acid identity with the rat 5-HT(3A) subunit and 73% identity with the human 5-HT(3B) subunit. Despite a relatively low level of structural conservation, sequence analysis and functional studies suggest that the new rodent subunits are orthologues of the human 5-HT(3B) subunit. In common with homologous human receptors, rat heteromeric 5-HT(3) receptors displayed a substantially larger single-channel conductance than homomeric 5-HT(3A) receptors. In addition, the rat heteromeric receptors were less sensitive to antagonism by tubocurarine. However, in contrast to human heteromeric receptors, those of the rat displayed pronounced inward rectification of both the whole-cell and single-channel current amplitudes. Transcripts of the mouse 5-HT(3A) and 5-HT(3B) subunits are coexpressed in several cell lines that possess endogenous 5-HT(3) receptors. In addition, treatment of rat PC12 cells with nerve growth factor induced expression of both subunit mRNAs, with a similar time course for accumulation of each transcript. The combination of functional data and expression patterns is consistent with the existence of heteromeric 5-HT(3) receptors in rodent neurons.
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Affiliation(s)
- M C Hanna
- The Institute for Genomic Research, Rockville, Maryland Department of Pharmacology, The George Washington University Medical Center, Washington, D.C., USA
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30
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Gunthorpe MJ, Peters JA, Gill CH, Lambert JJ, Lummis SC. The 4'lysine in the putative channel lining domain affects desensitization but not the single-channel conductance of recombinant homomeric 5-HT3A receptors. J Physiol 2000; 522 Pt 2:187-98. [PMID: 10639097 PMCID: PMC2269757 DOI: 10.1111/j.1469-7793.2000.00187.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
The 5-HT3 receptor is a transmitter-gated ion channel of the Cys-loop superfamily. Uniquely, 5-HT3 receptor subunits (5-HT3A and 5-HT3B) possess a positively charged lysine residue within the putative channel lining M2 domain (4' position). Using whole cell recording techniques, we examined the role of this residue in receptor function using wild-type (WT) and mutant 5-HT3A receptor subunits of murine origin transiently expressed in human embryonic kidney (HEK 293) cells. WT 5-HT3A receptors mediated rapidly activating currents in response to 5-HT (10-90 % rise time, 103 ms; EC50, 2.34 microM; Hill coefficient, nH, 2.87). The currents rectified inwardly, reversed in sign at a potential of -9 mV and desensitized in the continuous presence of agonist (half-time of desensitization, t(1/2), 2.13 s). 5-HT3A receptor subunits in which the 4'lysine was mutated to arginine, glutamine, serine or glycine formed functional receptors. 5-HT EC50 values were approximately 2-fold lower than for WT 5-HT3A receptors, but Hill coefficients, kinetics of current activation, rectification, and reversal potentials were unaltered. Each of the mutants desensitized more slowly than the WT 5-HT3A receptor, with the arginine and glycine mutations exhibiting the greatest effect (5-fold reduction). The rank order of effect was arginine > glycine > serine > glutamine. The single-channel conductance of the WT 5-HT3A receptor, as assessed by fluctuation analysis of macroscopic currents, was 390 fS. A similar value was obtained for the 4'lysine mutant receptors. Thus it appears unlikely that 4'lysine is exposed to the channel lumen. Mutation of residues immediately adjacent to 4'lysine to glutamate or lysine resulted in lack of receptor expression or function. We conclude that 4'lysine does not form part of the channel lining, but may play an important role in 5-HT3 receptor desensitization.
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Affiliation(s)
- M J Gunthorpe
- Division of Neurobiology, Laboratory of Molecular Biology, Medical Research Council Centre, Hills Road, Cambridge, UK
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31
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Mochizuki S, Miyake A, Furuichi K. Ion permeation properties of a cloned human 5-HT3 receptor transiently expressed in HEK 293 cells. Amino Acids 1999; 17:243-55. [PMID: 10582123 DOI: 10.1007/bf01366923] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Human 5-HT3 receptors expressed in HEK 293 cells were studied using patch-clamp techniques. The permeability ratios of cations to Na+ were Li+, 1.16; K+, 1.04; Rb+, 1.11; Cs+, 1.11; NMDG+, 0.04; Ca2+, 0.49, and Mg2+, 0.37. The permeability sequence of the alkali metal cations was Li+ > Rb+ = Cs+ > K+ > Na+. Increased external concentrations of Ca2+ or Mg2- decreased 5-HT-induced currents at all potentials tested in a voltage-independent manner. The single-channel conductance of human 5-HT3 receptors measured by fluctuation analysis of whole-cell currents was 790 +/- 100 fS. Differences in the basic properties of 5-HT3 receptors between species may explain interspecies differences in pharmacological properties.
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Affiliation(s)
- S Mochizuki
- Molecular Medicine Laboratories, Yamanouchi Pharmaceutical Co., Ltd., Ibaraki, Japan.
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32
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Abstract
1. To extend our knowledge of the site and mechanism of action of L-type Ca2+ channel antagonists on 5-HT3 receptors, whole-cell voltage clamp electrophysiology was used to investigate the action of one of these compounds, diltiazem, on the recombinant receptor expressed in human embryonic kidney (HEK) 293 cells. 2. Application of diltiazem with 5-HT (30 microM) caused an increase in the rate of receptor current decay, but did not significantly affect peak current (Ip), the EC50 or the Hill coefficient, indicating a non-competitive mechanism of action. Pre-application of the antagonist had no effect indicating that diltiazem mediates its effects by binding preferentially to the open state of the 5-HT3 receptor. 3. To examine the effects of diltiazem on the open state of the receptor in more detail we used 10 mM 5-hydroxyindole (5-OHi) to reduce receptor desensitisation. These experiments showed that diltiazem causes a rapid, reversible, block in the presence of agonist but can become trapped in the unliganded state of the receptor by prior washout of agonist. Dose-inhibition data yielded an IC50 of 5.5 microM and a Hill coefficient of 0.96; inhibition was slightly voltage dependent as the degree of blockade at +60 mV was reduced. 4. The Hill coefficient of near unity suggests a single molecule of diltiazem mediates inhibition and, indeed, kinetic analysis verified that the interaction of diltiazem with the 5-HT3 receptor was well described by a bimolecular reaction scheme. The results suggest that diltiazem acts by causing open-channel block of the 5-HT3 receptor.
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Affiliation(s)
- M J Gunthorpe
- Division of Neurobiology, Laboratory of Molecular Biology, Medical Research Council Centre, Hills Road, Cambridge CB2 2QH, UK
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33
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van Hooft JA, Vijverberg HP. Agonist and antagonist effects of apomorphine enantiomers on 5-HT3 receptors. Neuropharmacology 1998; 37:259-64. [PMID: 9680251 DOI: 10.1016/s0028-3908(98)00044-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Direct effects of the enantiomers of the classical dopamine receptor ligand apomorphine on 5-HT3 receptors were examined in NIE-115 neuroblastoma cells in whole-cell voltage clamp mode. R(-)-apomorphine (R(-)APO; 3-300 microM) evokes a small, transient inward ion current. At 30 microM, R(-)APO induces its maximum inward current, which is approximately 3% of the amplitude of the inward current induced by 10 microM 5-HT. The R(-)APO-induced current is completely and reversibly inhibited after superfusion of 50 nM of the selective 5-HT3 receptor antagonist MDL 72222 and after desensitization of the 5-HT3 receptors by 10 microM 5-HT. The results indicate that R(-)APO is a partial agonist at the 5-HT3 receptor. R(-)APO (30 microM) evokes a depolarization of the membrane potential with an amplitude which is 26% of the 10 microM 5-HT-induced depolarization. In addition, the 5-HT-induced depolarization is reduced (from 29 to 15 mV) after prolonged exposure of the cell to R(-)APO. S(+)-apomorphine (S(+)APO; 3-300 microM) does not evoke an ion current. Instead, S(+)APO antagonizes the 5-HT3 receptor with an IC50 of 32 microM. The combined results indicate that enantiomers of apomorphine act directly on 5-HT3 receptors, and suggest that the in vivo effects of apomorphine are partially attributable to a direct interaction with 5-HT3 receptors.
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Affiliation(s)
- J A van Hooft
- Research Institute of Toxicology, Utrecht University, The Netherlands
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34
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Brown AM, Hope AG, Lambert JJ, Peters JA. Ion permeation and conduction in a human recombinant 5-HT3 receptor subunit (h5-HT3A). J Physiol 1998; 507 ( Pt 3):653-65. [PMID: 9508827 PMCID: PMC2230823 DOI: 10.1111/j.1469-7793.1998.653bs.x] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
1. A human recombinant homo-oligomeric 5-HT3 receptor (h5-HT3A) expressed in a human embryonic kidney cell line (HEK 293) was characterized using the whole-cell recording configuration of the patch clamp technique. 2. 5-HT evoked transient inward currents (EC50 = 3.4 microM; Hill coefficient = 1.8) that were blocked by the 5-HT3 receptor antagonist ondansetron (IC50 = 103 pM) and by the non-selective agents metoclopramide (IC50 = 69 nM), cocaine (IC50 = 459 nM) and (+)-tubocurarine (IC50 = 2.8 microM). 3. 5-HT-induced currents rectified inwardly and reversed in sign (E5-HT) at a potential of -2.2 mV. N-Methyl-D-glucamine was finitely permeant. Permeability ratios PNa/PCs and PNMDG/PCs were 0.90 and 0.083, respectively. 4. Permeability towards divalent cations was assessed from measurements of E5-HT in media where Ca2+ and Mg2+ replaced Na+. PCa/PCs and PMg/PCs were calculated to be 1.00 and 0.61, respectively. 5. Single channel chord conductance (gamma) estimated from fluctuation analysis of macroscopic currents increased with membrane hyperpolarization from 243 fS at -40 mV to 742 fS at -100 mV. 6. Reducing [Ca2+]o from 2 to 0.1 mM caused an increase in the whole-cell current evoked by 5-HT. A concomitant reduction in [Mg2+]o produced further potentiation. Fluctuation analysis indicates that a voltage-independent augmentation of gamma contributes to this phenomenon. 7. The data indicate that homo-oligomeric receptors composed of h5-HT3A subunits form inwardly rectifying cation-selective ion channels of low conductance that are permeable to Ca2+ and Mg2+.
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Affiliation(s)
- A M Brown
- Department of Pharmacology and Neuroscience, Ninewells Hospital and Medical School, The University of Dundee, Dundee DD1 9SY, UK
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35
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Niemeyer MI, Lummis SC. Different efficacy of specific agonists at 5-HT3 receptor splice variants: the role of the extra six amino acid segment. Br J Pharmacol 1998; 123:661-6. [PMID: 9517385 PMCID: PMC1565215 DOI: 10.1038/sj.bjp.0701657] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
1. Whole cell voltage clamp electrophysiology and radioligand binding were used to examine the agonist characteristics of the two splice variants of the 5-HT3 receptor which have been cloned from neuronal cell lines. Homo-oligomeric 5-HT3 receptors were examined in HEK 293 cells stably transfected with either long (5-HT3-L) or short (5-HT3-S) receptor subunit DNAs. 2. Functional homo-oligomeric receptors were formed from both subunits, and responses to 5-HT3 receptor agonists (5-hydroxytryptamine (5-HT), 2-methyl 5-HT and m-chlorophenylbiguanide) were qualitatively similar. 3. Maximum currents (Rmax) elicited by the 5-HT3 receptor agonists m-chlorophenylbiguanide (mCPBG) and 2-methyl-5-HT (2-Me-5-HT), as compared to 5-HT, differed in the two splice variants: Rmax mCPBG/Rmax 5-HT values were 0.68+/-0.04 and 0.91+/-0.01 in 5-HT3-L and 5-HT3-S receptors, respectively. Comparable values for 2-Me-5-HT were 0.30+/-0.02 and 0.23+/-0.02. 4. Radioligand binding data showed no difference in affinity of agonist or antagonist binding sites; thus the six amino acid deletion appears to cause differences in agonist efficacy. 5. The role of the 6 amino acid insertion was further investigated by use of site-directed mutagenesis to create two mutant receptors, one where serine 286 was replaced with alanine, and the second where all 6 amino acids were replaced with alanines. 6. Examination of the mutant receptors when stably expressed in HEK 293 cells revealed agonist properties resembling long and not short 5-HT3 receptors. Thus specific amino acids in this region are not responsible for the observed differences. 7. The data show intracellular structure can have significant effects on ligand-gated ion channel function, and suggest that minor changes in structure may be responsible for differences in function observed when ligand-gated ion channel proteins are modulated intracellularly.
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Affiliation(s)
- M I Niemeyer
- Departmento de Ciencias Medicas, Universidad de Santiago de Chile
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36
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McMahon LL, Kauer JA. Hippocampal interneurons are excited via serotonin-gated ion channels. J Neurophysiol 1997; 78:2493-502. [PMID: 9356400 DOI: 10.1152/jn.1997.78.5.2493] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Hippocampal interneurons are excited via serotonin-gated ion channels. J. Neurophysiol. 78: 2493-2502, 1997. Serotonergic neurons of the median raphe nucleus heavily innervate hippocampal GABAergic interneurons located in stratum radiatum of area CA1, suggesting that this strong subcortical projection may modulate interneuron excitability. Using whole cell patch-clamp recording from interneurons in brain slices, we tested the effects of serotonin (5-HT) on the physiological properties of these interneurons. Serotonin produces a rapid inward current that persists when synaptic transmission is blocked by tetrodotoxin and cobalt, and is unaffected by ionotropic glutamate and gamma-aminobutyric acid (GABA) receptor antagonists. The 5-HT-induced current was independent of G-protein activation. Pharmacological evidence indicates that 5-HT directly excites these interneurons through activation of 5-HT3 receptors. At membrane potentials negative to -55 mV, the current-voltage (I-V) relationship of the 5-HT current displays a region of negative slope conductance. Therefore the response of interneurons to 5-HT strongly depends on membrane potential and increases greatly as cells are depolarized. Removal of extracellular calcium, but not magnesium, increases the amplitude of 5-HT-induced currents and removes the region of negative slope conductance, thereby linearizing the I-V relationship. The axons of 5-HT-responsive interneurons ramify widely within CA1; some of these interneurons also project to and arborize extensively in the dentate gyrus. The organization of these inhibitory connections strongly suggests that these cells regulate excitability of both CA1 pyramidal cells and dentate granule cells. As our results indicate that 5-HT may mediate fast excitatory synaptic transmission onto these interneurons, serotonergic inputs can simultaneously modulate the output of both hippocampus and dentate gyrus.
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Affiliation(s)
- L L McMahon
- Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA
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37
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Maswood N, Caldarola-Pastuszka M, Uphouse L. 5-HT3 receptors in the ventromedial nucleus of the hypothalamus and female sexual behavior. Brain Res 1997; 769:13-20. [PMID: 9374268 DOI: 10.1016/s0006-8993(97)00670-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Within the ventromedial nucleus of the hypothalamus (VMN), serotonin exerts a dual role in the control of female rat lordosis behavior. Most emphasis has been placed on 5-HT1A and 5-HT2 receptors, which inhibit and facilitate the behavior, respectively. In the current experiment, a potential role for VMN 5-HT3 receptors in the control of lordosis behavior was examined. Ovariectomized rats, hormonally primed with 25 microg estradiol benzoate and 500 microg progesterone, received bilateral VMN infusions with 100 ng, 250 ng or 500 ng of the 5-HT3 receptor antagonist, tropisetron. In these rats, there was a dose-dependent decline in both the lordosis to mount (L/M) ratio and in the quality of the lordosis reflex with 500 ng tropisetron producing the most consistent change in lordosis behavior. Relative to hormone-primed, ovariectomized rats, lordosis behavior of proestrous females was less affected by VMN infusions with the 5-HT3 receptor antagonist. The 5-HT3 receptor agonist, m-chlorophenylbiguanide (mCPBG), attenuated the effect of tropisetron; of the three mCPBG doses (500 ng, 1000 ng, 1500 ng) examined, 1000 ng was the most effective, perhaps because, alone, 1500 ng mCPBG slightly reduced lordosis behavior. These observations emphasize the potential role for VMN 5-HT3 receptors in the control of lordosis behavior.
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Affiliation(s)
- N Maswood
- Department of Biology, Texas Women's University, Denton 76204, USA
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Barann M, Göthert M, Bönisch H, Dybek A, Urban BW. 5-HT3 receptors in outside-out patches of N1E-115 neuroblastoma cells: basic properties and effects of pentobarbital. Neuropharmacology 1997; 36:655-64. [PMID: 9225291 DOI: 10.1016/s0028-3908(97)00059-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
A fast solution exchange system (Dilger and Brett, 1990; Biophysics Journal 57: 723-731) with an exchange rate < 1 msec was used to study 5-HT3 (5-HT; 5-hydroxytryptamine) receptor-mediated currents in superfused outside-out patches of N1E-115 mouse neuroblastoma cells. At negative membrane potentials, 5-HT induced inward currents in a concentration-dependent manner (IC50 = 3.8 microM, Hill coefficient = 1.8). The mean peak current at a near-maximally effective 5-HT concentration of 30 microM was 20.6 pA. The 5-HT3 receptor antagonist ondansetron (0.3 nM) reversibly inhibited the 5-HT (30 microM) signal by approximately 50%. The currents induced during application of 30 microM 5-HT for 2 sec were characterized by inward rectification, a monophasic onset (tau ON = 37.5 msec) and, after reaching a peak, a monophasic decay (desensitization; tau OFF = 391 msec). Onset and decay were slower at lower 5-HT concentrations. The recovery of fully desensitized patches required a washout period of 45 sec. Pentobarbital inhibited 5-HT-induced (30 microM) currents in a concentration-dependent manner. The maximally obtainable inhibition with a given pentobarbital concentration was reached already when it was exclusively coapplied with 5-HT (IC50 = 135 microM. Hill coefficient = -0.7), since additional preexposure for at least 45 sec did not alter the concentration-response curve of pentobarbital. In conclusion, outside-out patches of N1E-115 cells are suitable to study the kinetic properties of 5-HT3 receptor channels. The results obtained in this model with pentobarbital are compatible with the suggestion that the inhibitory action of pentobarbital on 5-HT3 receptors is dependent on the agonist-activated (open) channel.
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Affiliation(s)
- M Barann
- Institut für Pharmakologie und Toxikologie, Universität Bonn, Germany.
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van Hooft JA, Vijverberg HP. Full and partial agonists induce distinct desensitized states of the 5-HT3 receptor. J Recept Signal Transduct Res 1997; 17:267-77. [PMID: 9029495 DOI: 10.3109/10799899709036608] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
5-HT3 receptor-mediated ion currents evoked by the full agonists 5-hydroxy-tryptamine (5-HT), quaternary 5-HT (5-HTQ), meta-chlorophenylbiguanide (mCPBG) and the partial agonists dopamine and tryptamine have been investigated in whole-cell voltage clamp experiments on N1E-115 mouse neuroblastoma cells. All agonists desensitize the 5-HT3 receptor completely with a steep concentration dependence and a potency order of: mCPBG > 5-HTQ approximately 5-HT > > tryptamine > dopamine. The time course of recovery from desensitization depends on the agonist used. Recovery from partial agonist-induced desensitization is single exponential, whereas the desensitization induced by full agonists recovers with sigmoid kinetics, suggesting at least 3 transitions between 4 states. It is concluded that full and partial agonists induce distinct desensitized states.
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Affiliation(s)
- J A van Hooft
- Research Institute of Toxicology, Utrecht University, The Netherlands
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40
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Alkadhi KA, Salgado-Commissariat D, Hogan YH, Akpaudo SB. Induction and maintenance of ganglionic long-term potentiation require activation of 5-hydroxytryptamine (5-HT3) receptors. J Physiol 1996; 496 ( Pt 2):479-89. [PMID: 8910231 PMCID: PMC1160892 DOI: 10.1113/jphysiol.1996.sp021700] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
1. An extracellular recording technique was used to study the effects of 5-hydroxytryptamine (5-HT, serotonin) on the tetanus-induced long-term potentiation (LTP) of the nicotinic pathway of transmission in the superior cervical ganglion (SCG) of the rat. The postganglionic compound action potential (CAP), made submaximal by treatment with hexamethonium (O.4 mM), was used as an index of transmission in the ganglion. 2. Serotonin (10 microM) markedly enhanced the magnitude of LTP without affecting the post-tetanic potentiation (PTP). The serotonin (2-30 microM) concentration-response curve for LTP was bell shaped as no enhancement was seen with 30 microM serotonin. This may largely be due to activation of a 5-HT1 receptor subtype and not to desensitization. 3. When superfused before tetanus, the 5-HT1A receptor agonist 8-hydroxydipropylamino-tetralin (8-OH-DPAT, 5 microM) prevented the expression of LTP without affecting PTP. 4. Pretreatment of ganglia with the 5-HT2 receptor agonist R-(+)-dimethoxy-4-iodoamphetamine (R-(+)-DOI, 1 microM) enhanced the tetanus-induced LTP. Similar treatment with the 5-HT2 receptor antagonist ketanserin (3 microM) had no significant effect on LTP. 5. Pretreatment of ganglia with the 5-HT3 receptor agonist 1-m-(chlorophenyl) biguanide (m-CPGB, 1 microM), markedly increased (300%) the tetanus-induced LTP. Similar pretreatment with the 5-HT3 receptor antagonist 3-tropanyl-3,5-dichlorobenzoate (MDL 72222, 0.5 microM) completely prevented the expression of LTP. Fully expressed LTP was reversibly blocked by MDL 72222 when applied during the maintenance phase of LTP. 6. Tetanic stimulation of monoamine-depleted ganglia (from reserpine-pretreated rats, 3 mg kg-1 for 24 h) failed to induced LTP. 7. In monoamine-depleted ganglia, tetanus preceded by superfusion with m-CPBG readily induced LTP. MDL 72222 completely blocked this LTP. However in these ganglia tetanus failed to induced LTP when m-CPBG was given 2 min (during PTP) or 1 h after tetanus. 8. Tetanic stimulation of monoamine-depleted ganglia in the presence of R-(+)-DOI failed to induced LTP. 9. We conclude that tetanus-induced LTP of the SCG of the rat requires activation of 5-HT3 receptors both for induction and maintenance.
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Affiliation(s)
- K A Alkadhi
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, TX 77204-5515, USA.
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41
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Karim F, Roerig SC, Saphier D. Role of 5-hydroxytryptamine3 (5-HT3) antagonists in the prevention of emesis caused by anticancer therapy. Biochem Pharmacol 1996; 52:685-92. [PMID: 8765466 DOI: 10.1016/0006-2952(96)00346-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Most anticancer drugs are cytotoxic and produce various side-effects, among which nausea and vomiting are almost ubiquitous and usually extremely distressing to the patient. Cancer chemotherapy elicits two main phases of vomiting: an intense, acute phase of vomiting that occurs almost immediately following anti-cancer therapy and a milder, delayed phase of nausea and vomiting of longer duration. The mechanisms underlying the induction of nausea and vomiting after cancer chemotherapy are poorly understood but may be mediated by serotonin (5-hydroxytryptamine or 5-HT), particularly in the acute phase. Serotonin activates 5-HT3 receptors, which function as ligand-gated ion channels located either in the periphery and/or in the central nervous system to produce emesis, among other effects. The peripheral 5-HT3 receptors may be pharmacologically distinct from the central 5-HT3 receptors and may exhibit some association with GTP-binding proteins. In addition, different populations may exist as distinct subtypes of the same receptor. The 5-HT3 receptor antagonist ondansetron (GR 38032F) is effective in preventing the emesis induced by cytotoxic agents currently used in the treatment of many forms of cancer. Ondansetron has, comparatively, a much higher efficacy in the treatment of acute emesis following cancer chemotherapy than it does in the delayed phase, suggesting that the late phase of emesis may be mediated by other distinct mechanisms.
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Affiliation(s)
- F Karim
- Department of Pharmacology, Louisiana State University Medical Center, Shreveport 71130-3932, USA
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42
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Chesnoy-Marchais D. Potentiation of chloride responses to glycine by three 5-HT3 antagonists in rat spinal neurones. Br J Pharmacol 1996; 118:2115-25. [PMID: 8864550 PMCID: PMC1909912 DOI: 10.1111/j.1476-5381.1996.tb15651.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. Modulations of Cl- responses to glycine by 5-hydroxytryptamine ligands were studied in cultured spinal neurones, by the whole-cell recording technique. 2. Three 5-HT3 antagonists were found to potentiate reversibly responses to low concentrations of glycine. Potentiations were induced by micromolar concentrations of LY-278,584 (1-10 microM) and by concentrations of MDL-72222 or ICS-205,930 between 10 nM and 1 microM. 3. Potentiations were observed over the whole voltage range without any change in the reversal potential of the glycine responses and without affecting the resting conductance. 4. The degree of potentiation was variable among cells. It increased with the concentration of the modulator, but only up to 100 nM for MDL-72222 and ICS-205,930. 5. The potentiation appeared to result from an increase in the affinity for glycine of glycine receptors. 6. Neither the blockade of glycine uptake by Na+ removal, nor the excision of membrane patches prevented the potentiation. 7. At high concentrations (10 microM), both MDL-72222 and ICS-205,930 had, in contrast, a blocking effect on glycine responses. 8. Potentiation by LY-278,584 and a dose-dependent modulation by MDL-72222 were also observed for taurine responses. 9. The effects on glycine responses of various ligands of 5-HT3 receptors (including agonists) are discussed. The ability of LY-278,584, MDL-72222 and ICS-205,930 to potentiate glycine responses appears to be independent of their known 5-HT3 receptor antagonist properties. It would be interesting to look for chemically related drugs that would be specific potentiators of glycine responses.
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Jenkins A, Franks NP, Lieb WR. Actions of general anaesthetics on 5-HT3 receptors in N1E-115 neuroblastoma cells. Br J Pharmacol 1996; 117:1507-15. [PMID: 8730747 PMCID: PMC1909432 DOI: 10.1111/j.1476-5381.1996.tb15314.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
1. NIE-115 mouse neuroblastoma cells were studied under voltage clamp in the whole-cell patch-clamp configuration. Peak currents induced by bath application of 5-hydroxytryptamine (5-HT) were inwardly rectifying, reversed at 0.4 +/- 0.2 mV (mean +/- s.e.mean), and were approximately half-inhibited (at 1 microM 5-HT) by 2 nM of the 5-HT3 selective antagonist MDL-72222 (3-tropanyl-3,5-dichlorobenzoate). 2. Peak inward currents activated by a low concentration of 5-HT at a holding potential of -50 mV were potentiated by volatile general anaesthetics. At their human minimum alveolar concentrations (MACs), the degree of potentiation increased in the order isoflurane < halothane < enflurane < methoxyflurane. Potentiation by methoxyflurane was independent of membrane potential in the range -70 mV to +40 mV. The reversal potential was the same in the presence and absence of methoxyflurane. 3. Methoxyflurane shifted the 5-HT dose-response curve to lower 5-HT concentrations, without significantly changing the Hill coefficient or maximum response. The EC50 concentration for 5-HT decreased from 1.86 +/- 0.02 microM to 1.07 +/- 0.11 microM (means +/- s.e.mean) due to the presence of 1 MAC (270 microM) methoxyflurane. 4. In contrast to the volatile anaesthetics, the barbiturate anaesthetic, thiopentone, inhibited the 5-HT3 receptor. Hill analysis of thiopentone dose-response data gave an average IC50 = 117 +/- 8 microM thiopentone and Hill coefficient = 1.6 +/- 0.2 (means +/- s.e.mean). These parameters were not significantly different for data obtained at 5-HT concentrations above and below the control EC50 concentration for 5-HT, consistent with non-competitive inhibition. 5. The n-alcohols occupied an intermediate position between the volatile and barbiturate anaesthetics. The lower alcohols (butanol and hexanol) potentiated 5-HT responses at low alcohol concentrations but inhibited them at high concentrations. In contrast, the higher alcohols (octanol, decanol, dodecanol, tridecanol, tetradecanol and pentadecanol) produced no potentiation, but only inhibition, at all alcohol concentrations. 6. Inhibition of the 5-HT3 receptor by the n-alcohols exhibited a cutoff in potency similar to those previously found for tadpoles, luciferase enzymes and a neuronal nicotinic acetylcholine receptor channel.
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Affiliation(s)
- A Jenkins
- Biophysics Section, Blackett Laboratory, Imperial College of Science, Technology and Medicine, South Kensington, London
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van Hooft JA, Vijverberg HP. Selection of distinct conformational states of the 5-HT3 receptor by full and partial agonists. Br J Pharmacol 1996; 117:839-46. [PMID: 8851499 PMCID: PMC1909396 DOI: 10.1111/j.1476-5381.1996.tb15269.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. 5-Hydroxytryptamine 5-HT3 receptor-mediated ion currents evoked by 5-HT, quaternary 5-HT (5-HTQ), meta-chlorophenylbiguanide (mCPBG), dopamine and tryptamine in N1E-115 mouse neuroblastoma cells have been investigated in whole-cell voltage clamp and single channel patch clamp experiments. 2. The concentration-dependent activation and desensitization of the ion currents evoked by the agonists yield the potency order: mCPBG > 5-HTQ approximately 5-HT >> tryptamine > dopamine, and the efficacy order: 5-HT approximately mCPBG approximately 5-HTQ >> dopamine approximately tryptamine. Thus, 5-HT, 5-HTQ and mCPBG are full agonists, whereas dopamine and tryptamine are partial agonists at the 5-HT3 receptor. 3. Full and partial agonists cause complete cross-desensitization and activate single channels with similar conductances and open lifetimes. This shows that full and partial agonists act on the same population of 5-HT3 receptors. 4. The time course of recovery from desensitization depends on the agonist used. Recovery from partial agonist-induced desensitization is single exponential, whereas the desensitization induced by full agonists recovers with sigmoid kinetics, suggesting at least 3 steps between 4 states. 5. During the process of recovery from cross-desensitization, the full agonists activate a larger fraction of the 5-HT3 receptors than the partial agonists, irrespective of the agonist used to induce desensitization. 6. It is concluded that full and partial agonists induce distinct desensitized states and, during recovery from desensitization, recognize distinct conformations of unoccupied 5-HT3 receptors. This conformational selection is likely to account for the different efficacies of full and partial 5-HT3, receptor agonists.
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Affiliation(s)
- J A van Hooft
- Research Institute of Toxicology, Utrecht University, Netherlands
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45
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Green KA, Harris SJ, Cottrell GA. Dopamine directly activates a ligand-gated channel in snail neurones. Pflugers Arch 1996; 431:639-44. [PMID: 8596710 DOI: 10.1007/bf02191914] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Synaptically released dopamine is known to evoke fast as well as slow synaptic potentials in neurones of gastropod molluscs. Here evidence is presented that the fast excitatory response to dopamine is mediated by the direct activation of a ligand-gated channel: unitary currents were observed in outside-out patches of neurones exposed to dopamine, and the response persisted in the presence of intracellular guanosine 5'-o-(2-thiobiphosphate), GDP[beta-S], a condition known to block G-protein-coupled responses to dopamine and other agents. In whole-cell recordings, the fast response desensitized very rapidly; it was less desensitized in outside-out patches, suggesting dependence of desensitization on an intracellular factor. The response to dopamine was blocked by D-tubocurarine and strychnine (both probably by channel blockade), by apomorphine, chlorpromazine and relatively high doses of (+/-)-sulpiride and spiperone. The channel conducts predominantly monovalent cations. Unexpectedly, the fast response to dopamine was also observed in an identified dopaminergic neurone when maintained in isolation in culture. The receptors on the dopaminergic neurone were unevenly distributed, being more abundant on the axon-hillock, axon and neurite terminals.
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Affiliation(s)
- K A Green
- School of Biological and Medical Studies, University of St. Andrews Fife, UK
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46
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Barann M, Ruppert K, Göthert M, Bönisch H. Increasing effect of ethanol on 5-HT3 receptor-mediated 14C-guanidinium influx in N1E-115 neuroblastoma cells. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1995; 352:149-56. [PMID: 7477437 DOI: 10.1007/bf00176768] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
N1E-115 mouse neuroblastoma cells were used to study the influence of ethanol on the 5-HT- and veratridine-induced influx of 14C-guanidinium via the 5-HT3 receptor channel and the fast sodium channel, respectively. Ethanol (10-100 mM) concentration-dependently increased the 5-HT-induced 14C-guanidinium influx, leaving the basal and veratridine (100 microM)-induced influx unaffected. The increasing effect of ethanol (100 mM) was observed at all 5-HT concentrations investigated; accordingly, ethanol increased the maximum response to 5-HT. Whereas in the absence of ethanol the concentration-response curve for 5-HT was bell-shaped, this was no longer the case when ethanol (100 mM) was present in the incubation buffer; the descending branch of the concentration-response curve for 5-HT at concentrations above 300 microM was virtually no longer observed. When, in the presence of substance P (10 microM) the 5-HT-induced 14C-guanidinium influx was already enhanced, the ability of ethanol (100 mM) to increase the 5-HT-induced influx was considerably diminished (by 72%). Preincubation of N1E-115 cells with 5-HT caused a decay of the subsequent 5-HT response ("desensitization") which was dependent on the duration of preincubation; ethanol (100 mM) did not affect the rate of this decay of the 5-HT response. The 5-HT (30 microM)-induced 14C-guanidinium influx was also increased by methanol (100 mM) and n-propanol (100 mM). The rank order of the increasing effect of the n-alkanols (at 100 mM) was: methanol < ethanol < n-propanol; i.e. the degree of enhancement increased with the lipophilicity of the alcohols.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Barann
- Institut für Pharmakologie und Toxikologie, Universität Bonn, Germany
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47
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Fan P, Oz M, Zhang L, Weight FF. Effect of cocaine on the 5-HT3 receptor-mediated ion current in Xenopus oocytes. Brain Res 1995; 673:181-4. [PMID: 7606430 DOI: 10.1016/0006-8993(94)01316-a] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The cloned 5-HT3 receptor from NCB-20 neuroblastoma cells was expressed in Xenopus oocytes. In these oocytes, 5-HT, the selective 5-HT3 receptor agonists, 2-methyl-5-HT and m-chlorophenylbiguanide activated an inward current which was sensitive to the specific 5-HT3 receptor antagonist LY278584. Cocaine (0.1 to 10 microM) reversibly inhibited the current activated by 1 microM 5-HT in a concentration-dependent manner. The IC50 value is 0.7 microM and the apparent Hill coefficient is 1.55. This effect of cocaine was not dependent on membrane potential. Cocaine also produced a parallel shift of the 5-HT concentration-response curve to the right and did not reduce the maximal current induced by 5-HT. In the presence of 3 microM cocaine, the EC50 value of 5-HT was increased from 3.08 microM to 6.1 microM. Other local anesthetics such as tricaine and lidocaine also inhibited the current induced by 5-HT. These results suggest that the 5-HT3 receptors expressed in Xenopus oocytes exhibit properties similar to those in sensory neurons and neuroblastoma cells and were blocked by cocaine in a competitive manner.
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Affiliation(s)
- P Fan
- Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
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48
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Gill CH, Peters JA, Lambert JJ. An electrophysiological investigation of the properties of a murine recombinant 5-HT3 receptor stably expressed in HEK 293 cells. Br J Pharmacol 1995; 114:1211-21. [PMID: 7620711 PMCID: PMC1510359 DOI: 10.1111/j.1476-5381.1995.tb13335.x] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
1. The pharmacological and biophysical properties of a recombinant 5-HT3 receptor have been studied by use of patch-clamp techniques applied to HEK 293 cells stably transfected with the murine 5-HT3 R-A cDNA. 2. At a holding potential of -60 mV, 77% of cells investigated responded to ionophoretically applied 5-HT with an inward current. Such currents were unaffected by methysergide (1 microM), or ketanserin (1 microM), but were antagonized in a concentration-dependent and reversible manner by the selective 5-HT3 receptor antagonist, ondansetron (IC50 = 440 pM) and the non-selective antagonists (+)-tubocurarine (IC50 = 1.8 nM) and metoclopramide (IC50 50 nM). 3. The 5-HT-induced current reversed in sign (E5-HT) at approximately -2mV and exhibited inward rectification. The influence of extra- and intracellular ion substitutions upon E5-HT indicates the 5-HT-evoked current to be mainly mediated by a mixed monovalent cation conductance. 4. Calcium and magnesium (0.1-10 nM) produced a concentration-dependent, voltage-independent, inhibition of the 5-HT-induced response. Zinc (0.3-300 microM) exerted a biphasic effect with low concentrations enhancing, and high concentrations depressing, the 5-HT-evoked current. 5. Fluctuation analysis of inward currents evoked by a low (1 microM) concentration of 5-HT suggests the current to be mediated by the opening of channels with a conductance of 420 fS. 6. The pharmacological and biophysical properties of the 5-HT3 R-A are similar to those previously described for 5-HT3 receptors native to murine neuroblastoma cell lines, with the exception that the function of the recombinant receptor was enhanced by low concentrations of zinc. This observation suggests that the properties of the native receptor are not completely represented by the 5-HT3 R-A subunit alone.
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Affiliation(s)
- C H Gill
- Department of Pharmacology and Clinical Pharmacology, Ninewells Hospital and Medical School, University of Dundee
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Newberry NR, Cheshire SH, Gilbert MJ. Evidence that the 5-HT3 receptors of the rat, mouse and guinea-pig superior cervical ganglion may be different. Br J Pharmacol 1995; 102:615-20. [PMID: 1364827 PMCID: PMC1917933 DOI: 10.1111/j.1476-5381.1991.tb12221.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
1. Using grease-gap recordings from the isolated superior cervical ganglion of mouse, rat and guinea-pig, we have compared the depolarization evoked by 5-hydroxytryptamine (5-HT) with that evoked by the selective 5-HT3 receptor agonist 2-methyl-5-HT (2-Me-5-HT). 2. The maximum depolarization induced by 2-Me-5-HT was smaller than that induced by 5-HT in all three species, and particularly in the guinea-pig. 3. The 5-HT2 receptor antagonist ketanserin (1 microM) caused a clear rightward shift of the dose-response curve to 5-HT on the guinea-pig ganglion, but not on the mouse or rat ganglion. Spiperone (0.03 microM) had a quantitatively similar action to ketanserin (0.1 microM) on the 5-HT dose-response curve of the guinea-pig ganglion. Ketanserin had no significant effect on the dose-response curve to 2-Me-5-HT on any of these ganglia. 4. Using 2-Me-5-HT as the agonist, we determined the pA2 values for two 5-HT3 receptor antagonists. The potency of ICS 205-930 varied by approximately 100 fold between the species and that of (+)-tubocurarine varied by over 1000 fold. The differences in the pA2 values of these compounds varied independently among the species. 5. We conclude that 5-HT3 receptors are present on the superior cervical ganglion from the rat, mouse and guinea-pig, but these receptors may be pharmacologically distinct from each other. In addition, the depolarization of the guinea-pig superior cervical ganglion by low concentrations of 5-HT is largely mediated by ketanserin-sensitive receptors.
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Affiliation(s)
- N R Newberry
- Merck, Sharp and Dohme Research Labs, Neuroscience Research Centre, Harlow, Essex
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50
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Hussy N, Lukas W, Jones KA. Functional properties of a cloned 5-hydroxytryptamine ionotropic receptor subunit: comparison with native mouse receptors. J Physiol 1994; 481 ( Pt 2):311-23. [PMID: 7537814 PMCID: PMC1155931 DOI: 10.1113/jphysiol.1994.sp020441] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
1. A comparative study of the whole-cell and single-channel properties of cloned and native mouse 5-hydroxytryptamine ionotropic receptors (5-HT3) was undertaken using mammalian cell lines expressing the cloned 5-HT3 receptor subunit A (5-HT3R-A), superior cervical ganglia (SCG) neurones and N1E-115 cells. 2. No pharmacological difference was found in the sensitivity to the agonists 5-HT and 2-methyl-5-HT, or to the antagonists d-tubocurare and 3-tropanyl-3,5-dichlorobenzoate (MDL-72222). 3. Current-voltage (I-V) relationships of whole-cell currents showed inward rectification in the three preparations. Rectification was stronger both in cells expressing the 5-HT3R-A subunit and in N1E-115 cells when compared with SCG neurones. 4. No clear openings could be resolved in 5-HT-activated currents in patches excised from cells expressing the 5-HT3R-A subunit or N1E-115 cells. Current fluctuation analysis of whole-cell and excised-patch records revealed a slope conductance of 0.4-0.6 pS in both preparations. Current-voltage relationships of these channels showed strong rectification that fully accounted for the whole-cell voltage dependence. 5. In contrast, single channels of about 10 pS were activated by 5-HT in patches excised from SCG neurones. The weak voltage dependence of their conductance did not account completely for the rectification of whole-cell currents. A lower unitary conductance (3.4 pS) was inferred from whole-cell noise analysis. 6. We conclude that the receptor expressed from the cloned cDNA is indistinguishable from the 5-HT3 receptor of N1E-115 cells, suggesting an identical structure for these two receptors. The higher conductance and different voltage dependence of the 5-HT3 receptor in SCG neurones might indicate the participation of an additional subunit in the structure of native ganglionic 5-HT3 receptors. Homo-oligomeric 5-HT3R-A channels may also be present as suggested by the lower conductance estimated by whole-cell noise analysis.
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Affiliation(s)
- N Hussy
- Glaxo Institute for Molecular Biology, Geneva, Switzerland
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