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Ferron L, Zamponi GW. A tale of two calcium channels: structural pharmacology of Cav2.1 and Cav3.2. Cell Res 2024; 34:401-402. [PMID: 38702487 PMCID: PMC11143244 DOI: 10.1038/s41422-024-00961-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/06/2024] Open
Affiliation(s)
- Laurent Ferron
- Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Department of Clinical Neurosciences, Cumming School of Medicine, University of Calgary, Calgary, Canada
| | - Gerald W Zamponi
- Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Department of Clinical Neurosciences, Cumming School of Medicine, University of Calgary, Calgary, Canada.
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2
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Li Z, Cong Y, Wu T, Wang T, Lou X, Yang X, Yan N. Structural basis for different ω-agatoxin IVA sensitivities of the P-type and Q-type Ca v2.1 channels. Cell Res 2024; 34:455-457. [PMID: 38443561 PMCID: PMC11143261 DOI: 10.1038/s41422-024-00940-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Accepted: 02/14/2024] [Indexed: 03/07/2024] Open
Affiliation(s)
- Zhangqiang Li
- Beijing Frontier Research Center for Biological Structures, State Key Laboratory of Membrane Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, China.
| | - Ye Cong
- Beijing Frontier Research Center for Biological Structures, State Key Laboratory of Membrane Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, China
| | - Tong Wu
- Beijing Frontier Research Center for Biological Structures, State Key Laboratory of Membrane Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, China
| | - Tongtong Wang
- Beijing Frontier Research Center for Biological Structures, State Key Laboratory of Membrane Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, China
| | - Xinyao Lou
- Beijing Frontier Research Center for Biological Structures, State Key Laboratory of Membrane Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, China
| | - Xinyu Yang
- Beijing Frontier Research Center for Biological Structures, State Key Laboratory of Membrane Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, China
| | - Nieng Yan
- Beijing Frontier Research Center for Biological Structures, State Key Laboratory of Membrane Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, China.
- Institute of Bio-Architecture and Bio-Interactions, Shenzhen Medical Academy of Research and Translation, Shenzhen, Guangdong, China.
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3
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Zhou K, Luo W, Liu T, Ni Y, Qin Z. Neurotoxins Acting at Synaptic Sites: A Brief Review on Mechanisms and Clinical Applications. Toxins (Basel) 2022; 15:18. [PMID: 36668838 PMCID: PMC9865788 DOI: 10.3390/toxins15010018] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2022] [Revised: 12/20/2022] [Accepted: 12/21/2022] [Indexed: 12/29/2022] Open
Abstract
Neurotoxins generally inhibit or promote the release of neurotransmitters or bind to receptors that are located in the pre- or post-synaptic membranes, thereby affecting physiological functions of synapses and affecting biological processes. With more and more research on the toxins of various origins, many neurotoxins are now widely used in clinical treatment and have demonstrated good therapeutic outcomes. This review summarizes the structural properties and potential pharmacological effects of neurotoxins acting on different components of the synapse, as well as their important clinical applications, thus could be a useful reference for researchers and clinicians in the study of neurotoxins.
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Affiliation(s)
- Kunming Zhou
- Department of Pharmacology and Laboratory of Aging and Nervous Diseases, College of Pharmaceutical Sciences, Suzhou Medical College of Soochow University, Suzhou 215123, China
| | - Weifeng Luo
- Department of Neurology and Clinical Research Center of Neurological Disease, The Second Affiliated Hospital of Soochow University, Suzhou 215004, China
| | - Tong Liu
- Institute of Pain Medicine and Special Environmental Medicine, Nantong University, Nantong 226019, China
| | - Yong Ni
- Department of Neurology and Clinical Research Center of Neurological Disease, The Second Affiliated Hospital of Soochow University, Suzhou 215004, China
| | - Zhenghong Qin
- Department of Pharmacology and Laboratory of Aging and Nervous Diseases, College of Pharmaceutical Sciences, Suzhou Medical College of Soochow University, Suzhou 215123, China
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4
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McArthur JR, Wen J, Hung A, Finol-Urdaneta RK, Adams DJ. µ-Theraphotoxin Pn3a inhibition of Ca V3.3 channels reveals a novel isoform-selective drug binding site. eLife 2022; 11:e74040. [PMID: 35858123 PMCID: PMC9342953 DOI: 10.7554/elife.74040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Accepted: 07/19/2022] [Indexed: 11/13/2022] Open
Abstract
Low voltage-activated calcium currents are mediated by T-type calcium channels CaV3.1, CaV3.2, and CaV3.3, which modulate a variety of physiological processes including sleep, cardiac pace-making, pain, and epilepsy. CaV3 isoforms' biophysical properties, overlapping expression, and lack of subtype-selective pharmacology hinder the determination of their specific physiological roles in health and disease. We have identified μ-theraphotoxin Pn3a as the first subtype-selective spider venom peptide inhibitor of CaV3.3, with >100-fold lower potency against the other T-type isoforms. Pn3a modifies CaV3.3 gating through a depolarizing shift in the voltage dependence of activation thus decreasing CaV3.3-mediated currents in the normal range of activation potentials. Paddle chimeras of KV1.7 channels bearing voltage sensor sequences from all four CaV3.3 domains revealed preferential binding of Pn3a to the S3-S4 region of domain II (CaV3.3DII). This novel T-type channel pharmacological site was explored through computational docking simulations of Pn3a, site-directed mutagenesis, and full domain II swaps between CaV3 channels highlighting it as a subtype-specific pharmacophore. This research expands our understanding of T-type calcium channel pharmacology and supports the suitability of Pn3a as a molecular tool in the study of the physiological roles of CaV3.3 channels.
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Affiliation(s)
- Jeffrey R McArthur
- Illawarra Health and Medical Research Institute, University of WollongongWollongongAustralia
| | - Jierong Wen
- School of Science, RMIT UniversityMelbourneAustralia
| | - Andrew Hung
- School of Science, RMIT UniversityMelbourneAustralia
| | - Rocio K Finol-Urdaneta
- Illawarra Health and Medical Research Institute, University of WollongongWollongongAustralia
| | - David J Adams
- Illawarra Health and Medical Research Institute, University of WollongongWollongongAustralia
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5
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Thapa P, Stewart R, Sepela RJ, Vivas O, Parajuli LK, Lillya M, Fletcher-Taylor S, Cohen BE, Zito K, Sack JT. EVAP: A two-photon imaging tool to study conformational changes in endogenous Kv2 channels in live tissues. J Gen Physiol 2021; 153:212666. [PMID: 34581724 PMCID: PMC8480965 DOI: 10.1085/jgp.202012858] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2021] [Accepted: 09/03/2021] [Indexed: 12/29/2022] Open
Abstract
A primary goal of molecular physiology is to understand how conformational changes of proteins affect the function of cells, tissues, and organisms. Here, we describe an imaging method for measuring the conformational changes of the voltage sensors of endogenous ion channel proteins within live tissue, without genetic modification. We synthesized GxTX-594, a variant of the peptidyl tarantula toxin guangxitoxin-1E, conjugated to a fluorophore optimal for two-photon excitation imaging through light-scattering tissue. We term this tool EVAP (Endogenous Voltage-sensor Activity Probe). GxTX-594 targets the voltage sensors of Kv2 proteins, which form potassium channels and plasma membrane–endoplasmic reticulum junctions. GxTX-594 dynamically labels Kv2 proteins on cell surfaces in response to voltage stimulation. To interpret dynamic changes in fluorescence intensity, we developed a statistical thermodynamic model that relates the conformational changes of Kv2 voltage sensors to degree of labeling. We used two-photon excitation imaging of rat brain slices to image Kv2 proteins in neurons. We found puncta of GxTX-594 on hippocampal CA1 neurons that responded to voltage stimulation and retain a voltage response roughly similar to heterologously expressed Kv2.1 protein. Our findings show that EVAP imaging methods enable the identification of conformational changes of endogenous Kv2 voltage sensors in tissue.
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Affiliation(s)
- Parashar Thapa
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA
| | - Robert Stewart
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA
| | - Rebecka J Sepela
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA
| | - Oscar Vivas
- Center for Neuroscience, University of California, Davis, Davis, CA
| | - Laxmi K Parajuli
- Center for Neuroscience, University of California, Davis, Davis, CA
| | - Mark Lillya
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA
| | - Sebastian Fletcher-Taylor
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA.,The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA
| | - Bruce E Cohen
- The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA.,Division of Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA
| | - Karen Zito
- Center for Neuroscience, University of California, Davis, Davis, CA
| | - Jon T Sack
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA.,Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA
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6
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Tibery DV, de Souza ACB, Mourão CBF, do Nascimento JM, Schwartz EF. Purification and characterization of peptides Ap2, Ap3 and Ap5 (ω-toxins) from the venom of the Brazilian tarantula Acanthoscurria paulensis. Peptides 2021; 145:170622. [PMID: 34363923 DOI: 10.1016/j.peptides.2021.170622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Revised: 07/30/2021] [Accepted: 08/01/2021] [Indexed: 11/21/2022]
Abstract
Peptides isolated from spider venoms are of pharmacological interest due to their neurotoxic activity, acting on voltage-dependent ion channels present in different types of human body tissues. Three peptide toxins titled as Ap2, Ap3 and Ap5 were purified by RP-HPLC from Acanthoscurria paulensis venom. They were partially sequenced by MALDI In-source Decay method and their sequences were completed and confirmed by transcriptome analysis of the venom gland. The Ap2, Ap3 and Ap5 peptides have, respectively, 42, 41 and 46 amino acid residues, and experimental molecular masses of 4886.3, 4883.7 and 5454.7 Da, with the Ap2 peptide presenting an amidated C-terminus. Amongst the assayed channels - NaV1.1, NaV1.5, NaV1.7, CaV1.2, CaV2.1 and CaV2.2 - Ap2, Ap3 and Ap5 inhibited 20-30 % of CaV2.1 current at 1 μM concentration. Ap3 also inhibited sodium current in NaV1.1, Nav1.5 and Nav1.7 channels by 6.6 ± 1.91 % (p = 0.0276), 4.2 ± 1.09 % (p = 0.0185) and 16.05 ± 2.75 % (p = 0.0282), respectively. Considering that Ap2, Ap3 and Ap5 belong to the 'U'-unknown family of spider toxins, which has few descriptions of biological activity, the present work contributes to the knowledge of these peptides and demonstrates this potential as channel modulators.
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Affiliation(s)
- Diogo Vieira Tibery
- Laboratório de Neurofarmacologia, Departamento de Ciências Fisiológicas, Universidade de Brasília, Brasília, Brazil
| | | | - Caroline Barbosa Farias Mourão
- Laboratório de Neurofarmacologia, Departamento de Ciências Fisiológicas, Universidade de Brasília, Brasília, Brazil; Instituto Federal de Educação, Ciência e Tecnologia de Brasília, Campus Ceilândia, Brasília, DF, Brazil
| | | | - Elisabeth Ferroni Schwartz
- Laboratório de Neurofarmacologia, Departamento de Ciências Fisiológicas, Universidade de Brasília, Brasília, Brazil.
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Abstract
Voltage gated ion channels (VGICs) shape the electrical character of cells by undergoing structural changes in response to membrane depolarization. High-resolution techniques have provided a wealth of data on individual VGIC structures, but the conformational changes of endogenous channels in live cell membranes have remained unexplored. Here, we describe methods for imaging structural changes of voltage-gated K+ channels in living cells, using peptidyl toxins labeled with fluorophores that report specific protein conformations. These Endogenous Voltage-sensor Activity Probes (EVAPs) enable study of both VGIC allostery and function in the context of endogenous live-cell membranes under different physiological states. In this chapter, we describe methods for the synthesis, imaging, and analysis of dynamic EVAPs, which can report K+ channel activity in complex tissue preparations via 2-photon excitation microscopy, and environment-sensitive EVAPs, which report voltage-dependent conformational changes at the VGIC-toxin interface. The methods here present the utility of current EVAPs and lay the groundwork for the development of other probes that act by similar mechanisms. EVAPs can be correlated with electrophysiology, offering insight into the molecular details of endogenous channel function and allostery in live cells. This enables investigation of conformational changes of channels in their native, functional states, putting structures and models into a context of live-cell membranes. The expansive array of state-dependent ligands and optical probes should enable probes more generally for investigating the molecular motions of endogenous proteins.
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Affiliation(s)
- Robert Stewart
- Department of Physiology & Membrane Biology, University of California, Davis, CA, United States
| | - Bruce E Cohen
- The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, United States; Division of Molecular Biophysics & Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA, United States.
| | - Jon T Sack
- Department of Physiology & Membrane Biology, University of California, Davis, CA, United States; Department of Anesthesiology & Pain Medicine, University of California, Davis, CA, United States.
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Moya‐Díaz J, Bayonés L, Montenegro M, Cárdenas AM, Koch H, Doi A, Marengo FD. Ca 2+ -independent and voltage-dependent exocytosis in mouse chromaffin cells. Acta Physiol (Oxf) 2020; 228:e13417. [PMID: 31769918 DOI: 10.1111/apha.13417] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Revised: 11/19/2019] [Accepted: 11/20/2019] [Indexed: 12/11/2022]
Abstract
AIM It is widely accepted that the exocytosis of synaptic and secretory vesicles is triggered by Ca2+ entry through voltage-dependent Ca2+ channels. However, there is evidence of an alternative mode of exocytosis induced by membrane depolarization but lacking Ca2+ current and intracellular Ca2+ increase. In this work we investigated if such a mechanism contributes to secretory vesicle exocytosis in mouse chromaffin cells. METHODS Exocytosis was evaluated by patch-clamp membrane capacitance measurements, carbon fibre amperometry and TIRF. Cytosolic Ca2+ was estimated using epifluorescence microscopy and fluo-8 (salt form). RESULTS Cells stimulated by brief depolatizations in absence of extracellular Ca+2 show moderate but consistent exocytosis, even in presence of high cytosolic BAPTA concentration and pharmacological inhibition of Ca+2 release from intracellular stores. This exocytosis is tightly dependent on membrane potential, is inhibited by neurotoxin Bont-B (cleaves the v-SNARE synaptobrevin), is very fast (saturates with time constant <10 ms), it is followed by a fast endocytosis sensitive to the application of an anti-dynamin monoclonal antibody, and recovers after depletion in <5 s. Finally, this exocytosis was inhibited by: (i) ω-agatoxin IVA (blocks P/Q-type Ca2+ channel gating), (ii) in cells from knock-out P/Q-type Ca2+ channel mice, and (iii) transfection of free synprint peptide (interferes in P/Q channel-exocytic proteins association). CONCLUSION We demonstrated that Ca2+ -independent and voltage-dependent exocytosis is present in chromaffin cells. This process is tightly coupled to membrane depolarization, and is able to support secretion during action potentials at low basal rates. P/Q-type Ca2+ channels can operate as voltage sensors of this process.
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Affiliation(s)
- José Moya‐Díaz
- Instituto de Fisiología, Biología Molecular y Neurociencias Departamento de Fisiología y Biología Molecular y Celular Facultad de Ciencias Exactas y Naturales Universidad de Buenos AiresConsejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires Argentina
| | - Lucas Bayonés
- Instituto de Fisiología, Biología Molecular y Neurociencias Departamento de Fisiología y Biología Molecular y Celular Facultad de Ciencias Exactas y Naturales Universidad de Buenos AiresConsejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires Argentina
| | - Mauricio Montenegro
- Instituto de Fisiología, Biología Molecular y Neurociencias Departamento de Fisiología y Biología Molecular y Celular Facultad de Ciencias Exactas y Naturales Universidad de Buenos AiresConsejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires Argentina
| | - Ana M. Cárdenas
- Centro Interdisciplinario de Neurociencia de Valparaíso Facultad de Ciencias Universidad de Valparaíso Valparaíso Chile
| | - Henner Koch
- Center for Integrative Brain Research Seattle Children's Research Institute Seattle WA USA
- Department of Neurology and Epileptology Hertie‐Institute for Clinical Brain ResearchUniversity of Tübingen Tübingen Germany
| | - Atsushi Doi
- Department of Rehabilitation Graduate School of Health Science Kumamoto Health Science University Kumamoto Japan
| | - Fernando D. Marengo
- Instituto de Fisiología, Biología Molecular y Neurociencias Departamento de Fisiología y Biología Molecular y Celular Facultad de Ciencias Exactas y Naturales Universidad de Buenos AiresConsejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires Argentina
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Calorio C, Donno D, Franchino C, Carabelli V, Marcantoni A. Bud extracts from Salix caprea L. inhibit voltage gated calcium channels and catecholamines secretion in mouse chromaffin cells. PHYTOMEDICINE : INTERNATIONAL JOURNAL OF PHYTOTHERAPY AND PHYTOPHARMACOLOGY 2017; 36:168-175. [PMID: 29157811 DOI: 10.1016/j.phymed.2017.09.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Revised: 07/07/2017] [Accepted: 09/21/2017] [Indexed: 06/07/2023]
Abstract
BACKGROUND Salix caprea L. is an ornamental plant with prominent antioxidant activity. In the last decades Salix caprea bud extracts (SCBEs) have been used for the treatment of oxidative stress related disorders. PURPOSE A large part of cellular functions depends on the amount of intracellular Ca2+ concentration which in turn is mainly determined by Ca2+ ions movements across plasma membrane as well as by Ca2+ released from the stores. For better evaluating the mechanism of action of SCBEs, we focused on the effect of SCBEs on voltage gated Ca2+ channels (VGCCs) functioning and related catecholamines secretion in mouse chromaffin cells (MCCs). These latter are neuroendocrine cells that share a wide variety of functions with neurons. They are particularly interesting for studying the relationship between VGCCs activation and catecholamines secretion both in control and under stressful conditions. STUDY DESIGN AND METHODS We focused on the effect of SCBEs on VGCCs being these latter considered one of the main pathway of Ca2+ influx across plasma membrane. Ca2+ currents and capacitance changes were measured in patch clamp experiments performed in voltage clamp configuration. RESULTS We show that SCBEs inhibited VGCCs in a dose dependent manner. On average, the saturating concentration of SCBEs (SCBEsmax) is able to block 36% of the maximum Ca2+ current amplitude (ICa) without selectivity for L (ICa, L) or non-L type (ICa, non-L) Ca2+ channels. Furthermore, ICa inhibition is not followed by alteration of VGCCs gating kinetics, but is responsible for a marked decrease of Ca2+ dependent catecholamines secretion. CONCLUSION We conclude that the ability of SCBEs to inhibit VGCCs function, known to be potentiated during oxidative stress, could contribute to the already known antioxidant properties of Salix caprea L. We finally suggest that the inhibitory effect of SCBEs on catecholamines secretion may contribute to treat stress dependent cellular dysfunctions.
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Affiliation(s)
- Chiara Calorio
- Department of Drug Science and Technology, University of Torino, Corso Raffaello 30, 10125 Torino, Italy.
| | - Dario Donno
- Department of Agricultural, Forest and Food Sciences (DiSAFA), University of Torino, Largo Braccini 2, 10095 Grugliasco, To, Italy.
| | - Claudio Franchino
- Department of Drug Science and Technology, University of Torino, Corso Raffaello 30, 10125 Torino, Italy.
| | - Valentina Carabelli
- Department of Drug Science and Technology, University of Torino, Corso Raffaello 30, 10125 Torino, Italy.
| | - Andrea Marcantoni
- Department of Drug Science and Technology, University of Torino, Corso Raffaello 30, 10125 Torino, Italy.
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The Molecular Basis of Toxins' Interactions with Intracellular Signaling via Discrete Portals. Toxins (Basel) 2017; 9:toxins9030107. [PMID: 28300784 PMCID: PMC5371862 DOI: 10.3390/toxins9030107] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Revised: 03/02/2017] [Accepted: 03/04/2017] [Indexed: 12/20/2022] Open
Abstract
An understanding of the molecular mechanisms by which microbial, plant or animal-secreted toxins exert their action provides the most important element for assessment of human health risks and opens new insights into therapies addressing a plethora of pathologies, ranging from neurological disorders to cancer, using toxinomimetic agents. Recently, molecular and cellular biology dissecting tools have provided a wealth of information on the action of these diverse toxins, yet, an integrated framework to explain their selective toxicity is still lacking. In this review, specific examples of different toxins are emphasized to illustrate the fundamental mechanisms of toxicity at different biochemical, molecular and cellular- levels with particular consideration for the nervous system. The target of primary action has been highlighted and operationally classified into 13 sub-categories. Selected examples of toxins were assigned to each target category, denominated as portal, and the modulation of the different portal’s signaling was featured. The first portal encompasses the plasma membrane lipid domains, which give rise to pores when challenged for example with pardaxin, a fish toxin, or is subject to degradation when enzymes of lipid metabolism such as phospholipases A2 (PLA2) or phospholipase C (PLC) act upon it. Several major portals consist of ion channels, pumps, transporters and ligand gated ionotropic receptors which many toxins act on, disturbing the intracellular ion homeostasis. Another group of portals consists of G-protein-coupled and tyrosine kinase receptors that, upon interaction with discrete toxins, alter second messengers towards pathological levels. Lastly, subcellular organelles such as mitochondria, nucleus, protein- and RNA-synthesis machineries, cytoskeletal networks and exocytic vesicles are also portals targeted and deregulated by other diverse group of toxins. A fundamental concept can be drawn from these seemingly different toxins with respect to the site of action and the secondary messengers and signaling cascades they trigger in the host. While the interaction with the initial portal is largely determined by the chemical nature of the toxin, once inside the cell, several ubiquitous second messengers and protein kinases/ phosphatases pathways are impaired, to attain toxicity. Therefore, toxins represent one of the most promising natural molecules for developing novel therapeutics that selectively target the major cellular portals involved in human physiology and diseases.
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11
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Bourinet E, Zamponi GW. Block of voltage-gated calcium channels by peptide toxins. Neuropharmacology 2016; 127:109-115. [PMID: 27756538 DOI: 10.1016/j.neuropharm.2016.10.016] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Revised: 10/14/2016] [Accepted: 10/15/2016] [Indexed: 12/26/2022]
Abstract
Venoms from various predatory species, such as fish hunting molluscs scorpions, snakes and arachnids contain a large spectrum of toxins that include blockers of voltage-gated calcium channels. These peptide blockers act by two principal manners - physical occlusion of the pore and prevention of activation gating. Many of the calcium channel-blocking peptides have evolved to tightly occupy their binding pocket on the principal pore forming subunit of the channel, often rendering block poorly reversible. Moreover, several of the best characterized blocking peptides have developed a high degree of channel subtype selectivity. Here we give an overview of different types of calcium channel-blocking toxins, their mechanism of action, channel subtype specificity, and potential use as therapeutic agents. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'
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Affiliation(s)
- Emmanuel Bourinet
- Institute for Functional Genomics, CNRS UMR5203, INSERM U1191, University of Montpellier, LABEX ICST, Montpellier, France
| | - Gerald W Zamponi
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Canada.
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12
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Rose SJ, Kriener LH, Heinzer AK, Fan X, Raike RS, van den Maagdenberg AMJM, Hess EJ. The first knockin mouse model of episodic ataxia type 2. Exp Neurol 2014; 261:553-62. [PMID: 25109669 DOI: 10.1016/j.expneurol.2014.08.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Revised: 07/07/2014] [Accepted: 08/01/2014] [Indexed: 12/28/2022]
Abstract
Episodic ataxia type 2 (EA2) is an autosomal dominant disorder associated with attacks of ataxia that are typically precipitated by stress, ethanol, caffeine or exercise. EA2 is caused by loss-of-function mutations in the CACNA1A gene, which encodes the α1A subunit of the CaV2.1 voltage-gated Ca(2+) channel. To better understand the pathomechanisms of this disorder in vivo, we created the first genetic animal model of EA2 by engineering a mouse line carrying the EA2-causing c.4486T>G (p.F1406C) missense mutation in the orthologous mouse Cacna1a gene. Mice homozygous for the mutated allele exhibit a ~70% reduction in CaV2.1 current density in Purkinje cells, though surprisingly do not exhibit an overt motor phenotype. Mice hemizygous for the knockin allele (EA2/- mice) did exhibit motor dysfunction measurable by rotarod and pole test. Studies using Cre-flox conditional genetics explored the role of cerebellar Purkinje cells or cerebellar granule cells in the poor motor performance of EA2/- mice and demonstrate that manipulation of either cell type alone did not cause poor motor performance. Thus, it is possible that subtle dysfunction arising from multiple cell types is necessary for the expression of certain ataxia syndromes.
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Affiliation(s)
- Samuel J Rose
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Lisa H Kriener
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Ann K Heinzer
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA
| | - Xueliang Fan
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Robert S Raike
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Arn M J M van den Maagdenberg
- Department of Human Genetics, Leiden University Medical Centre, 2300 RC Leiden, The Netherlands; Department of Neurology, Leiden University Medical Centre, 2300 RC Leiden, The Netherlands
| | - Ellen J Hess
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA; Department of Neurology, Emory University School of Medicine, Atlanta, GA 30322, USA.
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13
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Pharmacological correction of gating defects in the voltage-gated Ca(v)2.1 Ca²⁺ channel due to a familial hemiplegic migraine mutation. Neuron 2014; 81:91-102. [PMID: 24411734 DOI: 10.1016/j.neuron.2013.10.056] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/07/2013] [Indexed: 11/20/2022]
Abstract
Voltage-gated ion channels exhibit complex properties, which can be targeted in pharmacological therapies for disease. Here, we report that the pro-oxidant, tert-butyl dihydroquinone (BHQ), modulates Ca(v)2.1 Ca²⁺ channels in ways that oppose defects in channel gating and synaptic transmission resulting from a familial hemiplegic migraine mutation (S218L). BHQ slows deactivation, inhibits voltage-dependent activation, and potentiates Ca²⁺-dependent facilitation of Ca(v)2.1 channels in transfected HEK293T cells. These actions of BHQ help offset the gain of function and reduced Ca²⁺-dependent facilitation of Ca(v)2.1 channels with the S218L mutation. Transgenic expression of the mutant channels at the Drosophila neuromuscular junction causes abnormally elevated evoked postsynaptic potentials and impaired synaptic plasticity, which are largely restored to the wild-type phenotypes by BHQ. Our results reveal a mechanism by which a Ca(v)2.1 gating modifier can ameliorate defects associated with a disease-causing mutation in Ca(v)2.1.
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Romanov RA, Rogachevskaja OA, Bystrova MF, Kolesnikov SS. Electrical excitability of taste cells. Mechanisms and possible physiological significance. BIOCHEMISTRY MOSCOW SUPPLEMENT SERIES A-MEMBRANE AND CELL BIOLOGY 2012. [DOI: 10.1134/s1990747812010126] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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15
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Beqollari D, Kammermeier PJ. The interaction between mGluR1 and the calcium channel Cav₂.₁ preserves coupling in the presence of long Homer proteins. Neuropharmacology 2012; 66:302-10. [PMID: 22659088 DOI: 10.1016/j.neuropharm.2012.05.038] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2011] [Revised: 05/18/2012] [Accepted: 05/21/2012] [Indexed: 11/29/2022]
Abstract
Group I metabotropic glutamate receptors (mGluR1 and 5) are G protein coupled receptors that regulate neuronal activity in a number of ways. Some of the most well studied functions of group I mGluRs, such as initiation of multiple forms of mGluR-dependent long-term depression, require receptor localization near the post-synaptic density (PSD). This localization is in turn dependent on the Homer family of scaffolding proteins which bind to a small motif on the distal C-termini of mGluR1 and 5, localize the receptors near the PSD, strengthen coupling to post-synaptic effectors and simultaneously uncouple the mGluRs from extra-synaptic effectors such as voltage dependent ion channels. Here the selectivity of this uncoupling process was examined by testing the ability of Homer-2b to uncouple mGluR1 from multiple voltage dependent calcium channels including Ca(V2.2) (N-type), Ca(V3.2) (T-type), and Ca(V2.1) (P/Q-type) expressed in rat sympathetic neurons from the superior cervical ganglion (SCG). Of these, only the mGluR1-Ca(V2.1) modulatory pathway was insensitive to Homer-2b expression. Uncoupling from this channel was achieved by co-expression of an mGluR1 C-terminal protein designed to disrupt a previously described direct interaction between these two proteins, suggesting that this interaction allows incorporation of Ca(V2.1) into the mGluR1/Homer signaling complex, thereby preserving modulation in the presence of scaffolding Homer proteins. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.
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Affiliation(s)
- Donald Beqollari
- University of Rochester Medical Center, Department of Pharmacology and Physiology, Rochester, NY 14642, USA
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16
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Lee CW, Eu YJ, Min HJ, Cho EM, Lee JH, Kim HH, Nah SY, Swartz KJ, Kim JI. Expression and characterization of recombinant kurtoxin, an inhibitor of T-type voltage-gated calcium channels. Biochem Biophys Res Commun 2011; 416:277-82. [PMID: 22093820 DOI: 10.1016/j.bbrc.2011.11.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Accepted: 11/01/2011] [Indexed: 10/15/2022]
Abstract
Kurtoxin, a 63-amino acid peptide stabilized by four disulfide bonds, is the first reported peptide inhibitor of T-type voltage-gated calcium channels. Although T-type calcium channels have been implicated in a number of disease states, including epilepsy, chronic pain, hypertension and cancer, the lack of selective inhibitors has slowed progress in understanding their precise roles. Kurtoxin is a potentially valuable tool with which to study T-type calcium channels. However, because of the limited availability of the native protein, little is known about the structure and molecular mechanism of kurtoxin. Here we report the expression of kurtoxin in Escherichia coli and the structural and functional characterization of the recombinant protein. The disulfide bond pairings and secondary structure of recombinant kurtoxin were characterized through enzymatic cleavage, mass analysis and CD spectroscopy. Recombinant kurtoxin almost completely inhibited the T-type calcium channel in a manner identical to the native toxin. The availability of recombinant kurtoxin that is identical to the native toxin should help in the study of T-type calcium channels and enable development of new strategies for producing even more-selective T-type calcium channel inhibitors and for investigating the molecular basis of the toxin-channel interactions.
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Affiliation(s)
- Chul Won Lee
- Department of Life Science, Gwangju Institute of Science and Technology, Gwangju 500-712, Republic of Korea
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17
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Peptide neurotoxins that affect voltage-gated calcium channels: a close-up on ω-agatoxins. Toxins (Basel) 2011; 3:17-42. [PMID: 22069688 PMCID: PMC3210452 DOI: 10.3390/toxins3010017] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2010] [Revised: 12/23/2010] [Accepted: 12/30/2010] [Indexed: 12/02/2022] Open
Abstract
Peptide neurotoxins found in animal venoms have gained great interest in the field of neurotransmission. As they are high affinity ligands for calcium, potassium and sodium channels, they have become useful tools for studying channel structure and activity. Peptide neurotoxins represent the clinical potential of ion-channel modulators across several therapeutic fields, especially in developing new strategies for treatment of ion channel-related diseases. The aim of this review is to overview the latest updates in the domain of peptide neurotoxins that affect voltage-gated calcium channels, with a special focus on ω-agatoxins.
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Gründer S, Chen X. Structure, function, and pharmacology of acid-sensing ion channels (ASICs): focus on ASIC1a. INTERNATIONAL JOURNAL OF PHYSIOLOGY, PATHOPHYSIOLOGY AND PHARMACOLOGY 2010; 2:73-94. [PMID: 21383888 PMCID: PMC3047259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 02/16/2010] [Accepted: 03/10/2010] [Indexed: 05/30/2023]
Abstract
Acid-sensing ion channels (ASICs) are H(+)-gated Na(+) channels, which are present in most, if not all, neurons. The typical ASIC current is transient and is elicited by a rapid drop in the extracellular pH. In the human genome, four genes for ASICs are present: asic1 - 4. In this review, we will focus on ASIC1a, one of the key subunits in the central nervous system. We will describe the structure of this channel, a topic that has enormously profited from the recent elucidation of the first crystal structure of an ASIC. We will then relate the ASIC1 structure to current models of the gating mechanism of ASICs. Finally, we will review the pharmacology of ASIC1a. Advances in the pharmacological inhibition of individual ASIC currents have greatly contributed to our current knowledge of the functional roles of this channel in physiology, including learning, memory, and fear conditioning, and in pathophysiological states, including the neurodegeneration accompanying stroke, and axonal degeneration in autoimmune inflammation.
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Affiliation(s)
- Stefan Gründer
- Department of Physiology, RWTH Aachen UniversityAachen, Germany
| | - Xuanmao Chen
- Department of Physiology, University of TorontoToronto, Canada
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Kreiner L, Christel CJ, Benveniste M, Schwaller B, Lee A. Compensatory regulation of Cav2.1 Ca2+ channels in cerebellar Purkinje neurons lacking parvalbumin and calbindin D-28k. J Neurophysiol 2009; 103:371-81. [PMID: 19906882 DOI: 10.1152/jn.00635.2009] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Ca(v)2.1 channels regulate Ca(2+) signaling and excitability of cerebellar Purkinje neurons. These channels undergo a dual feedback regulation by incoming Ca(2+) ions, Ca(2+)-dependent facilitation and inactivation. Endogenous Ca(2+)-buffering proteins, such as parvalbumin (PV) and calbindin D-28k (CB), are highly expressed in Purkinje neurons and therefore may influence Ca(v)2.1 regulation by Ca(2+). To test this, we compared Ca(v)2.1 properties in dissociated Purkinje neurons from wild-type (WT) mice and those lacking both PV and CB (PV/CB(-/-)). Unexpectedly, P-type currents in WT and PV/CB(-/-) neurons differed in a way that was inconsistent with a role of PV and CB in acute modulation of Ca(2+) feedback to Ca(v)2.1. Ca(v)2.1 currents in PV/CB(-/-) neurons exhibited increased voltage-dependent inactivation, which could be traced to decreased expression of the auxiliary Ca(v)beta(2a) subunit compared with WT neurons. Although Ca(v)2.1 channels are required for normal pacemaking of Purkinje neurons, spontaneous action potentials were not different in WT and PV/CB(-/-) neurons. Increased inactivation due to molecular switching of Ca(v)2.1 beta-subunits may preserve normal activity-dependent Ca(2+) signals in the absence of Ca(2+)-buffering proteins in PV/CB(-/-) Purkinje neurons.
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Affiliation(s)
- Lisa Kreiner
- Department of Molecular Physiology and Biophysics, University of Iowa, 51 Newton Road, Iowa City, IA 52242, USA
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20
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Dai G, Haedo RJ, Warren VA, Ratliff KS, Bugianesi RM, Rush A, Williams ME, Herrington J, Smith MM, McManus OB, Swensen AM. A High-Throughput Assay for Evaluating State Dependence and Subtype Selectivity of Cav2 Calcium Channel Inhibitors. Assay Drug Dev Technol 2008; 6:195-212. [DOI: 10.1089/adt.2008.136] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Affiliation(s)
- Ge Dai
- Merck Research Laboratories, Rahway, NJ
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21
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Richards KS, Swensen AM, Lipscombe D, Bommert K. Novel CaV2.1 clone replicates many properties of Purkinje cell CaV2.1 current. Eur J Neurosci 2008; 26:2950-61. [PMID: 18001290 DOI: 10.1111/j.1460-9568.2007.05912.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The P-type calcium current is mediated by a voltage-sensing CaV2.1 alpha subunit in combination with modulatory auxiliary subunits. In Purkinje neurones, this current has distinctively slow inactivation kinetics that may depend on alternative splicing of the alpha subunit and/or association with different CaVbeta subunits. To better understand the molecular components of P-type calcium current, we cloned a CaV2.1 cDNA from total mouse brain. The full-length CaV2.1 isoform that we isolated (GenBank AY714490) contains sequences recently shown to be present in Purkinje neurones. In agreement with previously published work, the alternatively spliced amino acid V421, implicated in slow inactivation, was not encoded in AY714490 and was absent from reverse transcription-polymerase chain reaction products generated from single Purkinje cells. Next, we studied the expression of the four known mouse auxiliary CaVbeta2 isoforms in Purkinje neurones. Confirmation of the presence of CaVbeta2a in Purkinje cells, previously shown by others to slow CaV2.1 kinetics, led us to characterize its influence on current dynamics. We studied currents generated by the clone AY714490 coexpressed in tsA201 cells with four different CaVbeta subunits. In addition to the well-documented slowing of open-state inactivation kinetics, coexpression with the CaVbeta2a subunit also protected CaV2.1 channels from closed-state inactivation and prevented the channel from inactivating during physiological trains of action potential-like stimuli. This strong resistance to inactivation parallels the property of Purkinje neurone P-type currents and is suggestive of a role for CaVbeta2a in modulating the inactivation properties of P-type calcium currents in Purkinje neurones.
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Abstract
The central and peripheral nervous systems express multiple types of ligand and voltage-gated calcium channels (VGCCs), each with specific physiological roles and pharmacological and electrophysiological properties. The members of the Ca(v)2 calcium channel family are located predominantly at presynaptic nerve terminals, where they are responsible for controlling evoked neurotransmitter release. The activity of these channels is subject to modulation by a number of different means, including alternate splicing, ancillary subunit associations, peptide and small organic blockers, G-protein-coupled receptors (GPCRs), protein kinases, synaptic proteins, and calcium-binding proteins. These multiple and complex modes of calcium channel regulation allow neurons to maintain the specific, physiological window of cytoplasmic calcium concentrations which is required for optimal neurotransmission and proper synaptic function. Moreover, these varying means of channel regulation provide insight into potential therapeutic targets for the treatment of pathological conditions that arise from disturbances in calcium channel signaling. Indeed, considerable efforts are presently underway to identify and develop specific presynaptic calcium channel blockers that can be used as analgesics.
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Affiliation(s)
- Alexandra E Kisilevsky
- Hotchkiss Brain Institute and Department of Physiology and Biophysics, University of Calgary, Calgary, Canada
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23
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Ovsepian SV, Friel DD. The leaner P/Q-type calcium channel mutation renders cerebellar Purkinje neurons hyper-excitable and eliminates Ca2+-Na+ spike bursts. Eur J Neurosci 2007; 27:93-103. [PMID: 18093175 DOI: 10.1111/j.1460-9568.2007.05998.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The leaner mouse mutation of the Cacna1a gene leads to a reduction in P-type Ca2+ current, the dominant Ca2+ current in Purkinje cells (PCs). Here, we compare the electro-responsiveness and structure of PCs from age-matched leaner and wild-type (WT) mice in pharmacological isolation from synaptic inputs in cerebellar slices. We report that compared with WT, leaner PCs exhibit lower current threshold for Na+ spike firing, larger subthreshold membrane depolarization, rapid adaptation followed by complete block of Na+ spikes upon strong depolarization, and fail to generate Ca2+-Na+ spike bursts. The Na+ spike waveforms in leaner PCs have slower kinetics, reduced spike amplitude and afterhyperpolarization. We show that a deficit in the P-type Ca2+ current caused by the leaner mutation accounts for most but not all of the changes in mutant PC electro-responsiveness. The selective P-type Ca2+ channel blocker, omega-agatoxin-IVA, eliminated differences in subthreshold membrane depolarization, adaptation of Na+ spikes upon strong current-pulse stimuli, Na+ spike waveforms and Ca2+-Na+ burst activity. In contrast, a lower current threshold for eliciting repetitive Na+ spikes in leaner PCs was still observed after blockade of the P-type Ca2+ current, suggesting secondary effects of the mutation that render PCs hyper-excitable. Higher input resistance, reduced whole-cell capacitance and smaller dendritic size accompanied the enhanced excitability in leaner PCs, indicative of developmental retardation in these cells caused by P/Q-type Ca2+ channel malfunction. Our data indicate that a deficit in P-type Ca2+ current leads to complex functional and structural changes in PCs, impairing their intrinsic and integrative properties.
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Affiliation(s)
- Saak V Ovsepian
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA.
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24
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Pluzhnikov K, Vassilevski A, Korolkova Y, Fisyunov A, Iegorova O, Krishtal O, Grishin E. ω-Lsp-IA, a novel modulator of P-type Ca2+ channels. Toxicon 2007; 50:993-1004. [PMID: 17888477 DOI: 10.1016/j.toxicon.2007.07.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2007] [Revised: 07/16/2007] [Accepted: 07/17/2007] [Indexed: 11/22/2022]
Abstract
A novel polypeptide, designated omega-Lsp-IA, which modulates P-type Ca(2+) channels, was purified from the venom of the spider Geolycosa sp. omega-Lsp-IA contains 47 amino acid residues and 4 intramolecular disulfide bridges. It belongs to a group of spider toxins affecting Ca(2+) channels and presumably forms the inhibitor cystine knot (ICK) fold. Peculiar structural features (a cluster of positively charged residues in the C-terminal loop of the peptide and a regular distribution of hydrophobic residues) that may play a decisive role in the omega-Lsp-IA mechanism of action were located. Recombinant omega-Lsp-IA was produced in prokaryotic expression system and was shown to be structurally and functionally identical to the native toxin. At saturating concentration (10nM), the peptide clearly slows down the activation kinetics and partially inhibits the amplitude of P-current in rat cerebellar Purkinje neurons. Prominent deceleration of the activation kinetics is manifested as the appearance of a five-fold slower component of the current activation. The specificity of action of omega-Lsp-IA on different Ca(2+) channel types was studied in isolated hippocampal neurons of rat. omega-Agatoxin IVA completely removed the effect of omega-Lsp-IA on the whole-cell Ca(2+) current. Therefore, omega-Lsp-IA appears to act specifically on P-type Ca(2+) channels.
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Affiliation(s)
- Kirill Pluzhnikov
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya, 16/10, 117997 Moscow, Russian Federation
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25
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Lisman JE, Raghavachari S, Tsien RW. The sequence of events that underlie quantal transmission at central glutamatergic synapses. Nat Rev Neurosci 2007; 8:597-609. [PMID: 17637801 DOI: 10.1038/nrn2191] [Citation(s) in RCA: 171] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The properties of synaptic transmission were first elucidated at the neuromuscular junction. More recent work has examined transmission at synapses within the brain. Here we review the remarkable progress in understanding the biophysical and molecular basis of the sequential steps in this process. These steps include the elevation of Ca2+ in microdomains of the presynaptic terminal, the diffusion of transmitter through the fusion pore into the synaptic cleft and the activation of postsynaptic receptors. The results give insight into the factors that control the precision of quantal transmission and provide a framework for understanding synaptic plasticity.
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Affiliation(s)
- John E Lisman
- Brandeis University, Department of Biology, MS 008, 415 South Street, Waltham, Massachusetts 02454-9110, USA.
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26
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King GF. Modulation of insect Cav channels by peptidic spider toxins. Toxicon 2007; 49:513-30. [PMID: 17197008 DOI: 10.1016/j.toxicon.2006.11.012] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2006] [Accepted: 11/17/2006] [Indexed: 10/23/2022]
Abstract
Insects have a much smaller repertoire of voltage-gated calcium (Ca(V)) channels than vertebrates. Drosophila melanogaster harbors only a single ortholog of each of the vertebrate Ca(V)1, Ca(V)2, and Ca(V)3 subtypes, although its basal inventory is expanded by alternative splicing and editing of Ca(V) channel transcripts. Nevertheless, there appears to be little functional plasticity within this limited panel of insect Ca(V) channels, since severe loss-of-function mutations in genes encoding the pore-forming alpha1 subunits in Drosophila are embryonic lethal. Since the primary role of spider venom is to paralyze or kill insect prey, it is not surprising that most, if not all, spider venoms contain peptides that potently modify the activity of these functionally critical insect Ca(V) channels. Unfortunately, it has proven difficult to determine the precise ion channel subtypes recognized by these peptide toxins since insect Ca(V) channels have significantly different pharmacology to their vertebrate counterparts, and cloned insect Ca(V) channels are not available for electrophysiological studies. However, biochemical and genetic studies indicate that some of these spider toxins might ultimately become the defining pharmacology for certain subtypes of insect Ca(V) channels. This review focuses on peptidic spider toxins that specifically target insect Ca(V) channels. In addition to providing novel molecular tools for ion channel characterization, some of these toxins are being used as leads to develop new methods for controlling insect pests.
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Affiliation(s)
- Glenn F King
- Division of Chemical and Structural Biology, Institute for Molecular Bioscience, University of Queensland, Brisbane Qld. 4072, Australia.
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Vieira LB, Pimenta AMC, Richardson M, Bemquerer MP, Reis HJ, Cruz JS, Gomez MV, Santoro MM, Ferreira-de-Oliveira R, Figueiredo SG, Snutch TP, Cordeiro MN. Leftward shift in the voltage-dependence for Ca2+ currents activation induced by a new toxin from Phoneutria reidyi (Aranae, Ctenidae) venom. Cell Mol Neurobiol 2006; 27:129-46. [PMID: 17151945 DOI: 10.1007/s10571-006-9123-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2006] [Accepted: 09/27/2006] [Indexed: 11/26/2022]
Abstract
Various neurotoxins have been described from the venom of the Brazilian spider Phoneutria nigriventer, but little is known about the venoms of the other species of this genus. In the present work, we describe the purification and some structural and pharmacological features of a new toxin (PRTx3-7) from Phoneutria reidyi that causes flaccid paralysis in mice. The observed molecular mass (4627.26 Da) was in accordance with the calculated mass for the amidated form of the amino acid sequence (4627.08 Da). The presence of an alpha-amidated C-terminus was confirmed by MS/MS analysis of the C-terminal peptide, isolated after enzymatic digestion of the native protein with Glu-C endoproteinase. The purified protein was injected (intracerebro-ventricular) into mice at dose levels of 5 microg/mouse causing immediate agitation and clockwise gyration, followed by the gradual development of general flaccid paralysis. PRTx3-7 at 1 microM inhibited by 20% the KCl-induced increase on [Ca2+]i in rat brain synaptosomes. The HEK cells permanently expressing L, N, P/Q and R HVA Ca2+ channels were also used to better characterize the pharmacological features of PRTx3-7. To our surprise, PRTx3-7 shifted the voltage-dependence for activation towards hyperpolarized membrane potentials for L (-4 mV), P/Q (-8 mV) and R (-5 mV) type Ca2+ currents. In addition, the new toxin also affected the steady state of inactivation of L-, N- and P/Q-type Ca2+ currents.
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Affiliation(s)
- L B Vieira
- Laboratório de Neurofarmacologia, Departamento de Farmacologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
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Abstract
Acid-sensing ion channels (ASICs) channels are proton-gated cationic channels mainly expressed in central and peripheric nervous system and related to the epithelial amiloride-sensitive Na(+) channels and to the degenerin family of ion channels. ASICs comprise four proteins forming functional channel subunits (ASIC1a, ASIC1b, ASIC2a, and ASIC3) and two proteins (ASIC2b and ASIC4) without yet known activators. Functional channels are activated by external pH variations ranging from pH(0.5) 6.8 to 4.0 and currents are characterized by either rapid kinetics of inactivation (ASIC1a, ASIC1b, ASIC3) or slow kinetics of inactivation (ASIC2a) and sometimes the presence of a plateau phase (ASIC3). ASIC1a and ASIC3, which are expressed in nociceptive neurons, have been implicated in inflammation and knockout mice studies support the role of ASIC3 in various pain processes. ASIC1a seems more related to synaptic plasticity, memory, learning and fear conditioning in the CNS. ASIC2a contributes to hearing in the cochlea, sour taste sensation, and visual transduction in the retina. The pharmacology of ASICs is limited to rather nonselective drugs such as amiloride, nonsteroid anti-inflammatory drugs, and neuropeptides. Recently, two peptides, PcTx1 and APETx2, isolated from a spider and a sea anemone, have been characterized as selective and high-affinity inhibitors for ASIC1a and ASIC3 channels, respectively. PcTx1 inhibits ASIC1a homomers with an affinity of 0.7 nM (IC(50)) without any effect on ASIC1a containing heteromers and thus helped to characterize ASIC1a homomeric channels in peripheric and central neurons. PcTx1 acts as a gating modifier since it shifts the channel from the resting to an inactivated state by increasing its affinity for H(+). APETx2 is less selective since it inhibits several ASIC3-containing channels (IC(50) from 63 nM to 2 microM) and to date its mode of action is unknown. Nevertheless, APETx2 structure is related to other sea anemone peptides, which act as gating modifiers on Nav and Kv channels.
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Affiliation(s)
- S Diochot
- Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, Sophia-Antipolis, 660 Route des Lucioles, 06560 Valbonne, France
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Abstract
Voltage-activated ion channels open and close in response to changes in membrane voltage, a process that is crucial for electrical signaling in the nervous system. The venom from many poisonous creatures contains a diverse array of small protein toxins that bind to voltage-activated channels and modify the gating mechanism. Hanatoxin and a growing number of related tarantula toxins have been shown to inhibit activation of voltage-activated potassium (K(v)) channels by interacting with their voltage-sensing domains. This review summarizes our current understanding of the mechanism by which these toxins alter gating, the location of the toxin receptor within K(v) channels and the disposition of this receptor with respect to the lipid membrane. The conservation of tarantula toxin receptors among voltage-activated ion channels will also be discussed.
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Affiliation(s)
- Kenton J Swartz
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
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30
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Abstract
Some of the most potent and specific inhibitors of voltage-gated calcium channels are peptide toxins that inhibit channel function not by occlusion of the channel pore, but rather by interfering with the voltage dependence and kinetics of channel opening and closing. Many such gating modifier toxins conform to the inhibitor cystine knot structural family and have primary sequence or functional mechanism similar to toxins that target voltage-gated sodium or potassium channels. This review introduces known gating modifiers of calcium channels, discusses the selectivity, binding sites, and mechanism of the toxin-channel interaction, and reviews the usefulness of these toxins as research tools and as the basis for novel calcium channel pharmacology and therapeutics.
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Affiliation(s)
- Stefan I McDonough
- Department of Neuroscience, Amgen, Inc., One Kendall Square Bldg 1000, Cambridge, MA 02139, USA
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31
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Fisyunov A, Tsintsadze V, Min R, Burnashev N, Lozovaya N. Cannabinoids modulate the P-type high-voltage-activated calcium currents in purkinje neurons. J Neurophysiol 2006; 96:1267-77. [PMID: 16738209 DOI: 10.1152/jn.01227.2005] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Endocannabinoids released by postsynaptic cells inhibit neurotransmitter release in many central synapses by activating presynaptic cannabinoid CB1 receptors. In particular, in the cerebellum, endocannabinoids inhibit synaptic transmission at granule cell to Purkinje cell synapses by modulating presynaptic calcium influx via N-, P/Q-, and R-type calcium channels. Using whole cell patch-clamp techniques, we show that in addition to this presynaptic action, both synthetic and endogenous cannabinoids inhibit P-type calcium currents in isolated rat Purkinje neurons independent of CB1 receptor activation. The IC50 for the anandamide (AEA)-induced inhibition of P-current peak amplitude was 1.04 +/- 0.04 microM. In addition, we demonstrate that all the tested cannabinoids in a physiologically relevant range of concentrations strongly accelerate inactivation of P currents. The effects of AEA cannot be attributed to the metabolism of AEA because a nonhydrolyzing analogue of AEA, methanandamide inhibited P-type currents with a similar efficacy. All effects of cannabinoids on P-type Ca2+ currents were insensitive to antagonists of CB1 cannabinoid or vanilloid TRPV1 receptors. In cerebellar slices, WIN 55,212-2 significantly affected spontaneous firing of Purkinje neurons in the presence of CB1 receptor antagonist, in a manner similar to that of a specific P-type channel antagonist, indicating a possible functional implication of the direct effects of cannabinoids on P current. Taken together these findings demonstrate a functionally important direct action of cannabinoids on P-type calcium currents.
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Affiliation(s)
- Alexander Fisyunov
- Department of Cellular Membranology, Bogomoletz Institute of Physiology, 4 Bogomoletz St., Kyiv 01024, Ukraine
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Chaudhuri D, Alseikhan BA, Chang SY, Soong TW, Yue DT. Developmental activation of calmodulin-dependent facilitation of cerebellar P-type Ca2+ current. J Neurosci 2006; 25:8282-94. [PMID: 16148236 PMCID: PMC6725527 DOI: 10.1523/jneurosci.2253-05.2005] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
P-type (CaV2.1) Ca2+ channels are a central conduit of neuronal Ca2+ entry, so their Ca2+ feedback regulation promises widespread neurobiological impact. Heterologous expression of recombinant CaV2.1 channels demonstrates that the Ca2+ sensor calmodulin can trigger Ca2+-dependent facilitation (CDF) of channel opening. This facilitation occurs when local Ca2+ influx through individual channels selectively activates the C-terminal lobe of calmodulin. In neurons, however, such calmodulin-mediated processes have yet to be detected, and CDF of native P-type current has thus far appeared different, arguably triggered by other Ca2+ sensing molecules. Here, in cerebellar Purkinje somata abundant with prototypic P-type channels, we find that the C-terminal lobe of calmodulin does produce CDF, and such facilitation augments Ca2+ entry during stimulation by repetitive action-potential and complex-spike waveforms. Beyond recapitulating key features of recombinant channels, these neurons exhibit an additional modulatory dimension: developmental upregulation of CDF during postnatal week 2. This phenomenon reflects increasing somatic expression of CaV2.1 splice variants that manifest CDF and progressive dendritic targeting of variants lacking CDF. Calmodulin-triggered facilitation is thus fundamental to native CaV2.1 and rapidly enhanced during early development.
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Affiliation(s)
- Dipayan Chaudhuri
- Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Abstract
Voltage-gated Ca2+ (Ca(v)) channels are found in all excitable cells and many nonexcitable cells, in which they govern Ca2+ influx, thereby contributing to determine a host of important physiological processes including gene transcription, muscle contraction, hormone secretion, and neurotransmitter release. The past years have seen some significant advances in our understanding of the functional, pharmacological, and molecular properties of Ca(v) channels. Molecular studies have revealed that several of these channels are oligomeric complexes consisting of an ion-conducting alpha1 subunit and auxiliary alpha2delta, beta, and gamma subunits. In addition, cloning of multiple Ca(v) channel alpha1 subunits has offered the opportunity to investigate the regulation of these proteins at the molecular level. The regulation of Ca(v) channels by intracellular second messengers constitutes a key mechanism for controlling Ca2+ influx. This review summarizes recent advances that have provided important clues to the underlying molecular mechanisms involved in the regulation of Ca(v) channels by protein phosphorylation, G-protein activation, and interactions with Ca(2+)-binding and SNARE proteins.
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Affiliation(s)
- Ricardo Felix
- Department of Physiology Biophysics, and Neuroscience, Center for Research and Advanced Studies of the National Polytechnic Institute, Cinvestav-IPN, Mexico City, Mexico.
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Chen X, Kalbacher H, Gründer S. The tarantula toxin psalmotoxin 1 inhibits acid-sensing ion channel (ASIC) 1a by increasing its apparent H+ affinity. ACTA ACUST UNITED AC 2005; 126:71-9. [PMID: 15955877 PMCID: PMC2266618 DOI: 10.1085/jgp.200509303] [Citation(s) in RCA: 162] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Acid-sensing ion channels (ASICs) are ion channels activated by extracellular protons. They are involved in higher brain functions and perception of pain, taste, and mechanical stimuli. Homomeric ASIC1a is potently inhibited by the tarantula toxin psalmotoxin 1. The mechanism of this inhibition is unknown. Here we show that psalmotoxin 1 inhibits ASIC1a by a unique mechanism: the toxin increases the apparent affinity for H+ of ASIC1a. Since ASIC1a is activated by H+ concentrations that are only slightly larger than the resting H+ concentration, this increase in H+ affinity is sufficient to shift ASIC1a channels into the desensitized state. As activation of ASIC1a has recently been linked to neurodegeneration associated with stroke, our results suggest chronic desensitization of ASIC1a by a slight increase of its H+ affinity as a possible way of therapeutic intervention in stroke.
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Affiliation(s)
- Xuanmao Chen
- Department of Physiology ll, University of Tübingen, 72076 Tübingen, Germany
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35
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Fisyunov A, Pluzhnikov K, Molyavka A, Grishin E, Lozovaya N, Krishtal O. Novel spider toxin slows down the activation kinetics of P-type Ca2+ channels in Purkinje neurons of rat. Toxicology 2005; 207:129-36. [PMID: 15590128 DOI: 10.1016/j.tox.2004.09.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2004] [Revised: 09/10/2004] [Accepted: 09/10/2004] [Indexed: 10/26/2022]
Abstract
We have identified a novel polypeptide toxin (Lsp-1) from the venom of the spider Lycosa (LS). Its effect has been examined on the P-type calcium channels in Purkinje neurons, using whole-cell patch-clamp. This toxin (at saturating concentration 7 nM) produces prominent (four-fold) deceleration of the activation kinetics and partial (71+/-6%) decrease of the amplitude of P-current without affecting either deactivation or inactivation kinetics. These effects are not use-dependent. They are partially reversible within a minute upon the wash-out of the toxin. Intracellular perfusion of Purkinje neurons with 100 microM of GDP or 2 microM of GTPgammaS, as well as strong depolarising pre-pulses (+100 mV), do not eliminate the action of Lsp-1 on P-channels indicating that down-modulation via guanine nucleotide-binding proteins (G-proteins) is not involved in the observed phenomenon. In view of extremely high functional significance of P-channels, the toxin can be suggested as a useful pharmacological tool.
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Affiliation(s)
- Alexander Fisyunov
- Department of Cellular Membranology, A.A. Bogomoletz Institute of Physiology, Bogomoletz Street 4, Kiev 01024, Ukraine
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Darszon A, Nishigaki T, Wood C, Treviño CL, Felix R, Beltrán C. Calcium Channels and Ca2+ Fluctuations in Sperm Physiology. INTERNATIONAL REVIEW OF CYTOLOGY 2005; 243:79-172. [PMID: 15797459 DOI: 10.1016/s0074-7696(05)43002-8] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Generating new life in animals by sexual reproduction depends on adequate communication between mature and competent male and female gametes. Ion channels are instrumental in the dialogue between sperm, its environment, and the egg. The ability of sperm to swim to the egg and fertilize it is modulated by ion permeability changes induced by environmental cues and components of the egg outer layer. Ca(2+) is probably the key messenger in this information exchange. It is therefore not surprising that different Ca(2+)-permeable channels are distinctly localized in these tiny specialized cells. New approaches to measure sperm currents, intracellular Ca(2+), membrane potential, and intracellular pH with fluorescent probes, patch-clamp recordings, sequence information, and heterologous expression are revealing how sperm channels participate in fertilization. Certain sperm ion channels are turning out to be unique, making them attractive targets for contraception and for the discovery of novel signaling complexes.
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Affiliation(s)
- Alberto Darszon
- Department of Developmental Genetics and Molecular Physiology, Institute of Biotechnology, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico 62210
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Wang JM, Roh SH, Kim S, Lee CW, Kim JI, Swartz KJ. Molecular surface of tarantula toxins interacting with voltage sensors in K(v) channels. ACTA ACUST UNITED AC 2004; 123:455-67. [PMID: 15051809 PMCID: PMC2217462 DOI: 10.1085/jgp.200309005] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The venom from spiders, scorpions, and sea anemone contain a rich diversity of protein toxins that interact with ion channel voltage sensors. Although atomic structures have been solved for many of these toxins, the surfaces that are critical for interacting with voltage sensors are poorly defined. Hanatoxin and SGTx are tarantula toxins that inhibit activation of K(v) channels by interacting with each of the four voltage sensors. In this study we set out to identify the active surface of these toxins by alanine-scanning SGTx and characterizing the interaction of each mutant with the K(v)2.1 channel. Examination of the concentration dependence for inhibition identified 15 mutants with little effect on the concentration dependence for toxin inhibition of the K(v)2.1 channel, and 11 mutants that display moderate to dramatic perturbations. Mapping of these results onto the structure of SGTx identifies one face of the toxin where mutations with pronounced perturbations cluster together, and a backside of the toxin where mutations are well tolerated. The active surface of SGTx contains a ring-like assembly of highly polar residues, with two basic residues that are particularly critical, concentrically arranged around a hydrophobic protrusion containing critical aliphatic and aromatic residues. These results identify the active surface of the toxin and reveal the types of side chains that are important for interacting with voltage sensors.
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Affiliation(s)
- Julia M Wang
- Molecular Physiology and Biophysics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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Abstract
Voltage-gated calcium channels are key sources of calcium entry into the cytosol of many excitable tissues. A number of different types of calcium channels have been identified and shown to mediate specialized cellular functions. Because of their fundamental nature, they are important targets for therapeutic intervention in disorders such as hypertension, pain, stroke, and epilepsy. Calcium channel antagonists fall into one of the following three groups: small inorganic ions, large peptide blockers, and small organic molecules. Inorganic ions nonselectively inhibit calcium entry by physical pore occlusion and are of little therapeutic value. Calcium-channel-blocking peptides isolated from various predatory animals such as spiders and cone snails are often highly selective blockers of individual types of calcium channels, either by preventing calcium flux through the pore or by antagonizing channel activation. There are many structure-activity-relation classes of small organic molecules that interact with various sites on the calcium channel protein, with actions ranging from selective high affinity block to relatively nondiscriminatory action on multiple calcium channel isoforms. Detailed interactions with the calcium channel protein are well understood for the dihydropyridine and phenylalkylamine drug classes, whereas we are only beginning to understand the molecular actions of some of the more recently discovered calcium channel blockers. Here, we provide a comprehensive review of pharmacology of high voltage-activated calcium channels.
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Affiliation(s)
- Clinton J Doering
- Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Dr. NW, Calgary, Canada T2N 4N1
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39
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Abstract
A variety of venomous animals produce small protein toxins that impair the function of voltage-dependent cation channels by affecting the motions of the voltage-sensor domains and altering the energetics of the opening of the channel. In this study, we investigate the location of the receptor for tarantula venom voltage-sensor toxins on the voltage-dependent K+ channel from Aeropyrum pernix (KvAP), an archeabacterial channel that is functionally inhibited by members of this toxin family. We show that it is possible to purify the same set of toxins from venom of the tarantula Grammostola spatulata using either the purified KvAP voltage-sensor domain or the full-length KvAP channel. The equivalence of toxin retention profiles for the two channel proteins implies that the tarantula voltage-sensor toxin receptor resides exclusively on the voltage-sensor domain and that the pore is not required for the toxin-channel interaction. We have identified and characterized the functional properties of a subset of the tarantula toxins that bind to the KvAP voltage-sensor domain. Some of these toxins, VSTX1 and GSMTX4, have been previously isolated, while others, VSTX2 and VSTX3, are new members of the tarantula voltage-sensor toxin family. Some but not all toxins that bind to the voltage-sensor domain affect voltage-dependent gating of KvAP channels in lipid membranes.
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Affiliation(s)
- Vanessa Ruta
- Howard Hughes Medical Institute, Rockefeller University, 1230 York Avenue, New York, New York 10021, USA
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Lin Y, McDonough SI, Lipscombe D. Alternative splicing in the voltage-sensing region of N-Type CaV2.2 channels modulates channel kinetics. J Neurophysiol 2004; 92:2820-30. [PMID: 15201306 DOI: 10.1152/jn.00048.2004] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The CaV2.2 gene encodes the functional core of the N-type calcium channel. This gene has the potential to generate thousands of CaV2.2 splice isoforms with different properties. However, the functional significance of most sites of alternative splicing is not established. The IVS3-IVS4 region contains an alternative splice site that is conserved evolutionarily among CaValpha1 genes from Drosophila to human. In CaV2.2, inclusion of exon 31a in the IVS3-IVS4 region is restricted to the peripheral nervous system, and its inclusion slows the speed of channel activation. To investigate the effects of exon 31a in more detail, we generated four tsA201 cell lines stably expressing CaV2.2 splice isoforms. Coexpression of auxiliary CaVbeta and CaValpha2delta subunits was required to reconstitute currents with the kinetics of N-type channels from neurons. Channels including exon 31a activated and deactivated more slowly at all voltages. Current densities were high enough in the stable cell lines co-expressing CaValpha2delta to resolve gating currents. The steady-state voltage dependence of charge movement was not consistently different between splice isoforms, but on gating currents from the exon 31a-containing CaV2.2 isoform decayed with a slower time course, corresponding to slower movement of the charge sensor. Exon 31a-containing CaV2.2 is restricted to peripheral ganglia; and the slower gating kinetics of CaV2.2 splice isoforms containing exon 31a correlated reasonably well with the properties of native N-type currents in sympathetic neurons. Our results suggest that alternative splicing in the S3-S4 linker influences the kinetics but not the voltage dependence of N-type channel gating.
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Affiliation(s)
- Yingxin Lin
- Deprtment of Neuroscience, Brown University, 192 Thayer St., Providence, RI 02912, USA
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41
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Allana TN, Lin JW. Relative distribution of Ca2+ channels at the crayfish inhibitory neuromuscular junction. J Neurophysiol 2004; 92:1491-500. [PMID: 15140907 DOI: 10.1152/jn.00287.2004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We investigated the Ca(2+) channel-synaptic vesicle topography at the inhibitor of the crayfish (Procambarus Clarkii) neuromuscular junction (NMJ) by analyzing the effect of different modes of Ca(2+) channel block on transmitter release. Initial identification of Ca(2+) channels revealed the presence of two classes, P and non-P-type with P-type channels governing approximately 70% of the total Ca(2+) influx. The remaining Ca(2+) influx was completely blocked by Cd(2+) but not by saturating concentrations of omega-conotoxins MVIIC and GVIA, or nifedipine and SNX-482. To examine the relative spatial distribution of Ca(2+) channels with respect to synaptic vesicles, we compared changes in inhibitory postsynaptic current amplitude and synaptic delay resulting from different spatial profiles of [Ca(2+)](i) around release sites. Specifically, addition of either [Mg(2+)](o), which decreases single-channel current, or omega-Aga IVA, which completely blocks P-type channels, prolonged synaptic delay by a similar amount when Ca(2+) influx block was <40%. Because non-P-type channels are able to compensate for blocked P-type channels, it suggests that these channels overlap considerably in their distribution. However, when Ca(2+) influx was blocked by approximately 50%, omega-Aga IVA increased delay significantly more than Mg(2+), suggesting that P-type channels are located closer than non-P-type channels to synaptic vesicles. This distribution of Ca(2+) channels was further supported by the observations that non-P-type channels are unable to trigger release in physiological saline and EGTA preferentially prolongs synaptic delay dominated by non-P-type channels when transmitter release is evoked with broad action potentials. We therefore conclude that although non-P-type channels do not directly trigger release under physiological conditions, their distribution partially overlaps with P-type channels.
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Affiliation(s)
- Tariq N Allana
- Department of Biology, Boston University, 5 Cummington St., Boston, MA 02215, USA
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Abstract
Agatoxins from Agelenopsis aperta venom target three classes of ion channels, including transmitter-activated cation channels, voltage-activated sodium channels, and voltage-activated calcium channels. The alpha-agatoxins are non-competitive, use-dependent antagonists of glutamate receptor channels, and produce rapid but reversible paralysis in insect prey. Their actions are facilitated by the micro-agatoxins, which shift voltage-dependent activation of neuronal sodium channels to more negative potentials, causing spontaneous transmitter release and repetitive action potentials. The omega-agatoxins target neuronal calcium channels, modifying their properties in distinct ways, either through gating modification (omega-Aga-IVA) or by reduction of unitary current (omega-Aga-IIIA). The alpha-agatoxins and omega-agatoxins modify both insect and vertebrate ion channels, while the micro-agatoxins are selective for insect channels. Agatoxins have been used as selective pharmacological probes for characterization of ion channels in the brain and heart, and have been evaluated as candidate biopesticides.
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Affiliation(s)
- Michael E Adams
- Department of Entomology, 5429 Boyce Hall, University of California, Riverside CA 92521, USA.
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Abstract
Over the last 20 years the combination of patch clamp and molecular biology techniques have resulted in an explosion in our knowledge of the different calcium channel types and their roles in physiology. A crucial component to this advance has been the discovery of specific blockers for different calcium channel types. These blockers have not only permitted researchers to assign specific functions to different channel types, but their specificity allowed them to be used to treat diseases that resulted from enhanced calcium channel function. In some cases, the enhanced calcium channel function is secondary to other problems leading to increased cellular excitability. The specificity of calcium channel blockers, however, has provided a means to treat symptoms of the pathophysiology until more effective treatments become available to address the underlying problems. The goal of this review is to introduce the various types of calcium channels, their primary physiologic roles, drugs that block these channels, and diseases that are currently being treated with these drugs.
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Affiliation(s)
- Keith S Elmslie
- Department of Physiology, Tulane University Health Science Center, New Orleans, Louisiana 70112, USA.
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Middleton RE, Warren VA, Kraus RL, Hwang JC, Liu CJ, Dai G, Brochu RM, Kohler MG, Gao YD, Garsky VM, Bogusky MJ, Mehl JT, Cohen CJ, Smith MM. Two tarantula peptides inhibit activation of multiple sodium channels. Biochemistry 2002; 41:14734-47. [PMID: 12475222 DOI: 10.1021/bi026546a] [Citation(s) in RCA: 191] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Two peptides, ProTx-I and ProTx-II, from the venom of the tarantula Thrixopelma pruriens, have been isolated and characterized. These peptides were purified on the basis of their ability to reversibly inhibit the tetrodotoxin-resistant Na channel, Na(V) 1.8, and are shown to belong to the inhibitory cystine knot (ICK) family of peptide toxins interacting with voltage-gated ion channels. The family has several hallmarks: cystine bridge connectivity, mechanism of channel inhibition, and promiscuity across channels within and across channel families. The cystine bridge connectivity of ProTx-II is very similar to that of other members of this family, i.e., C(2) to C(16), C(9) to C(21), and C(15) to C(25). These peptides are the first high-affinity ligands for tetrodotoxin-resistant peripheral nerve Na(V) channels, but also inhibit other Na(V) channels (IC(50)'s < 100 nM). ProTx-I and ProTx-II shift the voltage dependence of activation of Na(V) 1.5 to more positive voltages, similar to other gating-modifier ICK family members. ProTx-I also shifts the voltage dependence of activation of Ca(V) 3.1 (alpha(1G), T-type, IC(50) = 50 nM) without affecting the voltage dependence of inactivation. To enable further structural and functional studies, synthetic ProTx-II was made; it adopts the same structure and has the same functional properties as the native peptide. Synthetic ProTx-I was also made and exhibits the same potency as the native peptide. Synthetic ProTx-I, but not ProTx-II, also inhibits K(V) 2.1 channels with 10-fold less potency than its potency on Na(V) channels. These peptides represent novel tools for exploring the gating mechanisms of several Na(V) and Ca(V) channels.
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Affiliation(s)
- Richard E Middleton
- Department of Ion Channels, Merck Research Laboratories, Rahway, New Jersey, USA
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McDonough SI, Boland LM, Mintz IM, Bean BP. Interactions among toxins that inhibit N-type and P-type calcium channels. J Gen Physiol 2002; 119:313-28. [PMID: 11929883 PMCID: PMC2311392 DOI: 10.1085/jgp.20028560] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
A number of peptide toxins from venoms of spiders and cone snails are high affinity ligands for voltage-gated calcium channels and are useful tools for studying calcium channel function and structure. Using whole-cell recordings from rat sympathetic ganglion and cerebellar Purkinje neurons, we studied toxins that target neuronal N-type (Ca(V)2.2) and P-type (Ca(V)2.1) calcium channels. We asked whether different toxins targeting the same channels bind to the same or different sites on the channel. Five toxins (omega-conotoxin-GVIA, omega-conotoxin MVIIC, omega-agatoxin-IIIA, omega-grammotoxin-SIA, and omega-agatoxin-IVA) were applied in pairwise combinations to either N- or P-type channels. Differences in the characteristics of inhibition, including voltage dependence, reversal kinetics, and fractional inhibition of current, were used to detect additive or mutually occlusive effects of toxins. Results suggest at least two distinct toxin binding sites on the N-type channel and three on the P-type channel. On N-type channels, results are consistent with blockade of the channel pore by omega-CgTx-GVIA, omega-Aga-IIIA, and omega-CTx-MVIIC, whereas grammotoxin likely binds to a separate region coupled to channel gating. omega-Aga-IIIA produces partial channel block by decreasing single-channel conductance. On P-type channels, omega-CTx-MVIIC and omega-Aga-IIIA both likely bind near the mouth of the pore. omega-Aga-IVA and grammotoxin each bind to distinct regions associated with channel gating that do not overlap with the binding region of pore blockers. For both N- and P-type channels, omega-CTx-MVIIC binding produces complete channel block, but is prevented by previous partial channel block by omega-Aga-IIIA, suggesting that omega-CTx-MVIIC binds closer to the external mouth of the pore than does omega-Aga-IIIA.
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Abstract
Studies of Ca channels expressed in oocytes have identified kurtoxin as a promising tool for functional and structural studies of low-threshold T-type Ca channels. This peptide, isolated from the venomous scorpion Parabuthus transvaalicus, inhibits low-threshold alpha1G and alpha1H Ca channels expressed in oocytes with relatively high potency and high selectivity. Here we report its effects on Ca channel currents, carried by 5 mm Ba(2+) ions, in rat central and peripheral neurons. In thalamic neurons 500 nm kurtoxin inhibited T-type Ca channel currents almost completely (90.2 +/- 2.5% at -85 mV; n = 6). Its selectivity, however, was less than expected because it also reduced the composite high-threshold Ca channel current recorded in these cells (46.1 +/- 6.9% at -30 mV; n = 6). In sympathetic and thalamic neurons, 250-500 nm kurtoxin partially inhibited N-type and L-type Ca channel currents, respectively. It similarly reduced the high-threshold Ca channel current that remains after a blockade of P-type, N-type, and L-type Ca channels in thalamic neurons. In contrast, kurtoxin facilitated steady-state P-type Ba currents in Purkinje neurons (by 34.9 +/- 3.7%; n = 10). In all cases the kurtoxin effect was voltage-dependent and entailed a modification of channel gating. Exposure to kurtoxin slowed current activation kinetics, although its effects on deactivation varied with the channel types. Kurtoxin thus appears as a unique gating-modifier that interacts with different Ca channel types with high affinity. This unusual property and the complex gating modifications it induces may facilitate future studies of gating in voltage-dependent ion channels.
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47
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Sidach SS, Mintz IM. Kurtoxin, a gating modifier of neuronal high- and low-threshold ca channels. J Neurosci 2002; 22:2023-34. [PMID: 11896142 PMCID: PMC6758280] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023] Open
Abstract
Studies of Ca channels expressed in oocytes have identified kurtoxin as a promising tool for functional and structural studies of low-threshold T-type Ca channels. This peptide, isolated from the venomous scorpion Parabuthus transvaalicus, inhibits low-threshold alpha1G and alpha1H Ca channels expressed in oocytes with relatively high potency and high selectivity. Here we report its effects on Ca channel currents, carried by 5 mm Ba(2+) ions, in rat central and peripheral neurons. In thalamic neurons 500 nm kurtoxin inhibited T-type Ca channel currents almost completely (90.2 +/- 2.5% at -85 mV; n = 6). Its selectivity, however, was less than expected because it also reduced the composite high-threshold Ca channel current recorded in these cells (46.1 +/- 6.9% at -30 mV; n = 6). In sympathetic and thalamic neurons, 250-500 nm kurtoxin partially inhibited N-type and L-type Ca channel currents, respectively. It similarly reduced the high-threshold Ca channel current that remains after a blockade of P-type, N-type, and L-type Ca channels in thalamic neurons. In contrast, kurtoxin facilitated steady-state P-type Ba currents in Purkinje neurons (by 34.9 +/- 3.7%; n = 10). In all cases the kurtoxin effect was voltage-dependent and entailed a modification of channel gating. Exposure to kurtoxin slowed current activation kinetics, although its effects on deactivation varied with the channel types. Kurtoxin thus appears as a unique gating-modifier that interacts with different Ca channel types with high affinity. This unusual property and the complex gating modifications it induces may facilitate future studies of gating in voltage-dependent ion channels.
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Affiliation(s)
- Serguei S Sidach
- Department of Pharmacology and Experimental Therapeutics, Boston University Medical Center, Boston, Massachusetts 02118, USA
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48
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Bourinet E, Stotz SC, Spaetgens RL, Dayanithi G, Lemos J, Nargeot J, Zamponi GW. Interaction of SNX482 with domains III and IV inhibits activation gating of alpha(1E) (Ca(V)2.3) calcium channels. Biophys J 2001; 81:79-88. [PMID: 11423396 PMCID: PMC1301493 DOI: 10.1016/s0006-3495(01)75681-0] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
We have investigated the action of SNX482, a toxin isolated from the venom of the tarantula Hysterocrates gigas, on voltage-dependent calcium channels expressed in tsa-201 cells. Upon application of 200 nM SNX482, R-type alpha(1E) calcium channels underwent rapid and complete inhibition, which was only poorly reversible upon washout. However, upon application of strong membrane depolarizations, rapid and complete recovery from inhibition was obtained. Tail current analysis revealed that SNX482 mediated an approximately 70 mV depolarizing shift in half-activation potential, suggesting that the toxin inhibits alpha(1E) calcium channels by preventing their activation. Experiments involving chimeric channels combining structural features of alpha(1E) and alpha(1C) subunits indicated that the presence of the domain III and IV of alpha(1E) is a prerequisite for a strong gating inhibition. In contrast, L-type alpha(1C) channels underwent incomplete inhibition at saturating concentrations of SNX482 that was paralleled by a small shift in half-activation potential and which could be rapidly reversed, suggesting a less pronounced effect of the toxin on L-type calcium channel gating. We conclude that SNX482 does not exhibit unequivocal specificity for R-type channels, but highly effectively antagonizes their activation.
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Affiliation(s)
- E Bourinet
- Physiopathologie des Canaux Ioniques, Institut de Génétique Humaine, CNRS UPR1142, 34396 Montpellier Cedex 5, France.
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Feng ZP, Hamid J, Doering C, Bosey GM, Snutch TP, Zamponi GW. Residue Gly1326 of the N-type calcium channel alpha 1B subunit controls reversibility of omega-conotoxin GVIA and MVIIA block. J Biol Chem 2001; 276:15728-35. [PMID: 11279062 DOI: 10.1074/jbc.m100406200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We recently reported that amino acid residues contained within a putative EF hand motif in the domain III S5-H5 region of the alpha(1B) subunit affected the relative barium:calcium permeability of N-type calcium channels (Feng, Z. P., Hamid, J., Doering, C., Jarvis, S. E., Bosey, G. M., Bourinet, E., Snutch, T. P., and Zamponi, G. W. (2001) J. Biol. Chem. 276, 5726-5730). Since this region partially overlaps with residues previously implicated in block of the channel by omega-conotoxin GVIA, we assessed the effects of mutations in the putative EF hand domain on channel block by omega-conotoxin GVIA and the structurally related omega-conotoxin MVIIA. Both of the toxins irreversibly block the activity of wild type alpha(1B) N-type channels. We find that in addition to previously identified amino acid residues, residues in positions 1326 and 1332 are important determinants of omega-conotoxin GVIA blockade. Substitution of residue Glu(1332) to arginine slows the time course of development of block. Point mutations in position Gly(1326) to either arginine, glutamic acid, or proline dramatically decrease the time constant for development of the block. Additionally, in the G1326P mutant channel activity was almost completely recovered following washout. A qualitatively similar result was obtained with omega-conotoxin MVIIA, suggesting that common molecular determinants underlie block by these two toxins. Taken together the data suggest that residue Gly(1326) may form a barrier, which controls the access of peptide toxins to their blocking site within the outer vestibule of the channel pore and also stabilizes the toxin-channel interaction.
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Affiliation(s)
- Z P Feng
- Departments of Physiology & Biophysics and Pharmacology & Therapeutics, Neuroscience Research Group, University of Calgary, Calgary, Alberta T2N 4N1, Canada
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Abstract
The recognition of neuronal Ca channel diversity has led to considerable efforts to identify useful classification criteria. Here, we revisit the pharmacological definition of P- and Q-type Ca channels, which is based on their respective high and low sensitivity to the spider omega-agatoxin-IVA (omega-Aga-IVA), using whole-cell recordings of the Ca channel currents carried by 5 mM Ba(2+) in isolated rat subthalamic and sympathetic neurons. In subthalamic neurons, omega-Aga-IVA (1 microM) targeted multiple Ca channels. One population was blocked with high potency. These channels carried 50.4 +/- 3.4% (n = 5) of the control current and showed the same inactivation kinetics and voltage-dependent high affinity for omega-Aga-IVA as do prototypic P-type Ca channels. Other Ca channels were targeted with weaker potency. This heterogeneous population contributed to 14.0 +/- 1.7% (n = 5) of the control current. It included N-type Ca channels as well as high-threshold Ca channels that displayed the pharmacological signature of Q-type Ca channels but resembled P-type Ca channels in their gating properties. N-type Ca current block by omega-Aga-IVA (1 microM) was further investigated in sympathetic neurons, which mainly express this Ca channel type. Block was incomplete ( approximately 30% of the control current). Its relief at positive potentials was consistent with omega-Aga-IVA acting as a channel-gating modifier. These effects did not reflect a complete loss of selectivity, because omega-Aga-IVA (1 microM) had no effect on subthalamic Na and K currents or their T- and L-type Ca currents. Our data confirm that omega-Aga-IVA is a selective P-type Ca channel blocker. However, its diminished selectivity in the micromolar range limits its usefulness for functional studies of Q-type Ca channels.
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