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Abstract
Each heartbeat is initiated by the action potential, an electrical signal that depolarizes the plasma membrane and activates a cycle of calcium influx via voltage-gated calcium channels, calcium release via ryanodine receptors, and calcium reuptake and efflux via calcium-ATPase pumps and sodium-calcium exchangers. Agonists of the sympathetic nervous system bind to adrenergic receptors in cardiomyocytes, which, via cascading signal transduction pathways and protein kinase A (PKA), increase the heart rate (chronotropy), the strength of myocardial contraction (inotropy), and the rate of myocardial relaxation (lusitropy). These effects correlate with increased intracellular concentration of calcium, which is required for the augmentation of cardiomyocyte contraction. Despite extensive investigations, the molecular mechanisms underlying sympathetic nervous system regulation of calcium influx in cardiomyocytes have remained elusive over the last 40 years. Recent studies have uncovered the mechanisms underlying this fundamental biologic process, namely that PKA phosphorylates a calcium channel inhibitor, Rad, thereby releasing inhibition and increasing calcium influx. Here, we describe an updated model for how signals from adrenergic agonists are transduced to stimulate calcium influx and contractility in the heart.
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Affiliation(s)
- Arianne Papa
- Department of Physiology and Cellular Biophysics, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY, USA
| | - Jared Kushner
- Division of Cardiology, Department of Medicine, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY, USA;
| | - Steven O Marx
- Division of Cardiology, Department of Medicine, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY, USA;
- Department of Molecular Pharmacology and Therapeutics, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY, USA
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2
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The life cycle of voltage-gated Ca 2+ channels in neurons: an update on the trafficking of neuronal calcium channels. Neuronal Signal 2021; 5:NS20200095. [PMID: 33664982 PMCID: PMC7905535 DOI: 10.1042/ns20200095] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Revised: 02/10/2021] [Accepted: 02/15/2021] [Indexed: 01/26/2023] Open
Abstract
Neuronal voltage-gated Ca2+ (CaV) channels play a critical role in cellular excitability, synaptic transmission, excitation-transcription coupling and activation of intracellular signaling pathways. CaV channels are multiprotein complexes and their functional expression in the plasma membrane involves finely tuned mechanisms, including forward trafficking from the endoplasmic reticulum (ER) to the plasma membrane, endocytosis and recycling. Whether genetic or acquired, alterations and defects in the trafficking of neuronal CaV channels can have severe physiological consequences. In this review, we address the current evidence concerning the regulatory mechanisms which underlie precise control of neuronal CaV channel trafficking and we discuss their potential as therapeutic targets.
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3
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Papa A, Kushner J, Hennessey JA, Katchman AN, Zakharov SI, Chen BX, Yang L, Lu R, Leong S, Diaz J, Liu G, Roybal D, Liao X, del Rivero Morfin PJ, Colecraft HM, Pitt GS, Clarke O, Topkara V, Ben-Johny M, Marx SO. Adrenergic Ca V1.2 Activation via Rad Phosphorylation Converges at α 1C I-II Loop. Circ Res 2021; 128:76-88. [PMID: 33086983 PMCID: PMC7790865 DOI: 10.1161/circresaha.120.317839] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
RATIONALE Changing activity of cardiac CaV1.2 channels under basal conditions, during sympathetic activation, and in heart failure is a major determinant of cardiac physiology and pathophysiology. Although cardiac CaV1.2 channels are prominently upregulated via activation of PKA (protein kinase A), essential molecular details remained stubbornly enigmatic. OBJECTIVE The primary goal of this study was to determine how various factors converging at the CaV1.2 I-II loop interact to regulate channel activity under basal conditions, during β-adrenergic stimulation, and in heart failure. METHODS AND RESULTS We generated transgenic mice with expression of CaV1.2 α1C subunits with (1) mutations ablating interaction between α1C and β-subunits, (2) flexibility-inducing polyglycine substitutions in the I-II loop (GGG-α1C), or (3) introduction of the alternatively spliced 25-amino acid exon 9* mimicking a splice variant of α1C upregulated in the hypertrophied heart. Introducing 3 glycine residues that disrupt a rigid IS6-α-interaction domain helix markedly reduced basal open probability despite intact binding of CaVβ to α1C I-II loop and eliminated β-adrenergic agonist stimulation of CaV1.2 current. In contrast, introduction of the exon 9* splice variant in the α1C I-II loop, which is increased in ventricles of patients with end-stage heart failure, increased basal open probability but did not attenuate stimulatory response to β-adrenergic agonists when reconstituted heterologously with β2B and Rad or transgenically expressed in cardiomyocytes. CONCLUSIONS Ca2+ channel activity is dynamically modulated under basal conditions, during β-adrenergic stimulation, and in heart failure by mechanisms converging at the α1C I-II loop. CaVβ binding to α1C stabilizes an increased channel open probability gating mode by a mechanism that requires an intact rigid linker between the β-subunit binding site in the I-II loop and the channel pore. Release of Rad-mediated inhibition of Ca2+ channel activity by β-adrenergic agonists/PKA also requires this rigid linker and β-binding to α1C.
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Affiliation(s)
- Arianne Papa
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
- Department of Physiology and Cellular Biophysics
| | - Jared Kushner
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
| | - Jessica A. Hennessey
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
| | - Alexander N. Katchman
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
| | - Sergey I. Zakharov
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
| | - Bi-xing Chen
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
| | - Lin Yang
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
| | - Ree Lu
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
| | - Stephen Leong
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
| | - Johanna Diaz
- Department of Physiology and Cellular Biophysics
| | - Guoxia Liu
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
| | - Daniel Roybal
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
- Department of Pharmacology and Molecular Signaling, Columbia University, Vagelos College of Physicians and Surgeons
| | - Xianghai Liao
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
| | | | - Henry M. Colecraft
- Department of Physiology and Cellular Biophysics
- Department of Pharmacology and Molecular Signaling, Columbia University, Vagelos College of Physicians and Surgeons
| | - Geoffrey S. Pitt
- Cardiovascular Research Institute, Weill Cornell Medical College
| | | | - Veli Topkara
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
| | | | - Steven O. Marx
- Division of Cardiology, Department of Medicine, Columbia University, Vagelos College of Physicians and Surgeons, New York, NY 10032
- Department of Pharmacology and Molecular Signaling, Columbia University, Vagelos College of Physicians and Surgeons
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4
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Arteaga-Tlecuitl R, Sanchez-Sandoval AL, Ramirez-Cordero BE, Rosendo-Pineda MJ, Vaca L, Gomora JC. Increase of Ca V3 channel activity induced by HVA β1b-subunit is not mediated by a physical interaction. BMC Res Notes 2018; 11:810. [PMID: 30428904 PMCID: PMC6236959 DOI: 10.1186/s13104-018-3917-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Accepted: 11/09/2018] [Indexed: 01/13/2023] Open
Abstract
Objective Low voltage-activated (LVA) calcium channels are crucial for regulating oscillatory behavior in several types of neurons and other excitable cells. LVA channels dysfunction has been implicated in epilepsy, neuropathic pain, cancer, among other diseases. Unlike for High Voltage-Activated (HVA) channels, voltage-dependence and kinetics of currents carried by recombinant LVA, i.e., CaV3 channels, are quite similar to those observed in native currents. Therefore, whether these channels are regulated by HVA auxiliary subunits, remain controversial. Here, we used the α1-subunits of CaV3.1, CaV3.2, and CaV3.3 channels, together with HVA auxiliary β-subunits to perform electrophysiological, confocal microscopy and immunoprecipitation experiments, in order to further explore this possibility. Results Functional expression of CaV3 channels is up-regulated by all four β-subunits, although most consistent effects were observed with the β1b-subunit. The biophysical properties of CaV3 channels were not modified by any β-subunit. Furthermore, although β1b-subunits increased colocalization of GFP-tagged CaV3 channels and the plasma membrane of HEK-293 cells, western blots analysis revealed the absence of physical interaction between CaV3.3 and β1b-subunits as no co-immunoprecipitation was observed. These results provide solid evidence that the up-regulation of LVA channels in the presence of HVA-β1b subunit is not mediated by a high affinity interaction between both proteins. Electronic supplementary material The online version of this article (10.1186/s13104-018-3917-1) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Rogelio Arteaga-Tlecuitl
- Departamento de Neuropatología Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - Ana Laura Sanchez-Sandoval
- Departamento de Neuropatología Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - Belen Ernestina Ramirez-Cordero
- Departamento de Neuropatología Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - Margarita Jacaranda Rosendo-Pineda
- Departamento de Biología Celular y del Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - Luis Vaca
- Departamento de Biología Celular y del Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - Juan Carlos Gomora
- Departamento de Neuropatología Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico.
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5
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Wang D, Ragnarsson L, Lewis RJ. T-type Calcium Channels in Health and Disease. Curr Med Chem 2018; 27:3098-3122. [PMID: 30277145 DOI: 10.2174/0929867325666181001112821] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2018] [Revised: 08/28/2018] [Accepted: 08/30/2018] [Indexed: 12/12/2022]
Abstract
Low Voltage-Activated (LVA) T-type calcium channels are characterized by transient current and Low Threshold Spikes (LTS) that trigger neuronal firing and oscillatory behavior. Combined with their preferential localization in dendrites and their specific "window current", T-type calcium channels are considered to be key players in signal amplification and synaptic integration. Assisted by the emerging pharmacological tools, the structural determinants of channel gating and kinetics, as well as novel physiological and pathological functions of T-type calcium channels, are being uncovered. In this review, we provide an overview of structural determinants in T-type calcium channels, their involvement in disorders and diseases, the development of novel channel modulators, as well as Structure-Activity Relationship (SAR) studies that lead to rational drug design.
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Affiliation(s)
- Dan Wang
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, the University of Queensland, Brisbane Qld 4072, Australia
| | - Lotten Ragnarsson
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, the University of Queensland, Brisbane Qld 4072, Australia
| | - Richard J Lewis
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, the University of Queensland, Brisbane Qld 4072, Australia
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6
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Chemin J, Taiakina V, Monteil A, Piazza M, Guan W, Stephens RF, Kitmitto A, Pang ZP, Dolphin AC, Perez-Reyes E, Dieckmann T, Guillemette JG, Spafford JD. Calmodulin regulates Ca v3 T-type channels at their gating brake. J Biol Chem 2017; 292:20010-20031. [PMID: 28972185 PMCID: PMC5723990 DOI: 10.1074/jbc.m117.807925] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Revised: 09/19/2017] [Indexed: 01/10/2023] Open
Abstract
Calcium (Cav1 and Cav2) and sodium channels possess homologous CaM-binding motifs, known as IQ motifs in their C termini, which associate with calmodulin (CaM), a universal calcium sensor. Cav3 T-type channels, which serve as pacemakers of the mammalian brain and heart, lack a C-terminal IQ motif. We illustrate that T-type channels associate with CaM using co-immunoprecipitation experiments and single particle cryo-electron microscopy. We demonstrate that protostome invertebrate (LCav3) and human Cav3.1, Cav3.2, and Cav3.3 T-type channels specifically associate with CaM at helix 2 of the gating brake in the I-II linker of the channels. Isothermal titration calorimetry results revealed that the gating brake and CaM bind each other with high-nanomolar affinity. We show that the gating brake assumes a helical conformation upon binding CaM, with associated conformational changes to both CaM lobes as indicated by amide chemical shifts of the amino acids of CaM in 1H-15N HSQC NMR spectra. Intact Ca2+-binding sites on CaM and an intact gating brake sequence (first 39 amino acids of the I-II linker) were required in Cav3.2 channels to prevent the runaway gating phenotype, a hyperpolarizing shift in voltage sensitivities and faster gating kinetics. We conclude that the presence of high-nanomolar affinity binding sites for CaM at its universal gating brake and its unique form of regulation via the tuning of the voltage range of activity could influence the participation of Cav3 T-type channels in heart and brain rhythms. Our findings may have implications for arrhythmia disorders arising from mutations in the gating brake or CaM.
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Affiliation(s)
- Jean Chemin
- Institut de Génomique Fonctionnelle, CNRS, INSERM, Université de Montpellier, Montpellier F-34094, France
| | | | - Arnaud Monteil
- Institut de Génomique Fonctionnelle, CNRS, INSERM, Université de Montpellier, Montpellier F-34094, France
| | - Michael Piazza
- Departments of Chemistry, Waterloo, Ontario N2L 3G1, Canada
| | - Wendy Guan
- Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | | | - Ashraf Kitmitto
- Division of Cardiovascular Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9NT, United Kingdom
| | - Zhiping P Pang
- Department of Neuroscience and Cell Biology, Rutgers Robert Wood Johnson Medical School, New Brunswick, New Jersey 08901
| | - Annette C Dolphin
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, United Kingdom
| | - Edward Perez-Reyes
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908
| | | | | | - J David Spafford
- Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
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7
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Mustafá ER, López Soto EJ, Martínez Damonte V, Rodríguez SS, Lipscombe D, Raingo J. Constitutive activity of the Ghrelin receptor reduces surface expression of voltage-gated Ca 2+ channels in a Ca Vβ-dependent manner. J Cell Sci 2017; 130:3907-3917. [PMID: 29038230 DOI: 10.1242/jcs.207886] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Accepted: 10/04/2017] [Indexed: 12/15/2022] Open
Abstract
Voltage-gated Ca2+ (CaV) channels couple membrane depolarization to Ca2+ influx, triggering a range of Ca2+-dependent cellular processes. CaV channels are, therefore, crucial in shaping neuronal activity and function, depending on their individual temporal and spatial properties. Furthermore, many neurotransmitters and drugs that act through G protein coupled receptors (GPCRs), modulate neuronal activity by altering the expression, trafficking, or function of CaV channels. GPCR-dependent mechanisms that downregulate CaV channel expression levels are observed in many neurons but are, by comparison, less studied. Here we show that the growth hormone secretagogue receptor type 1a (GHSR), a GPCR, can inhibit the forwarding trafficking of several CaV subtypes, even in the absence of agonist. This constitutive form of GPCR inhibition of CaV channels depends on the presence of a CaVβ subunit. CaVβ subunits displace CaVα1 subunits from the endoplasmic reticulum. The actions of GHSR on CaV channels trafficking suggest a role for this signaling pathway in brain areas that control food intake, reward, and learning and memory.
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Affiliation(s)
- Emilio R Mustafá
- Electrophysiology Laboratory, Multidisciplinary Institute of Cell Biology (IMBICE), Universidad Nacional de La Plata - Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, and Comisión de Investigaciones de la Provincia de buenos Aires (CIC) Calle 526 1499-1579, B1906APM Tolosa, Buenos Aires, Argentina
| | - Eduardo J López Soto
- Department of Neuroscience, Brown University; Sidney E. Frank Hall for Life Sciences, 185 Meeting Street, Providence, Rhode Island 02912, USA
| | - Valentina Martínez Damonte
- Electrophysiology Laboratory, Multidisciplinary Institute of Cell Biology (IMBICE), Universidad Nacional de La Plata - Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, and Comisión de Investigaciones de la Provincia de buenos Aires (CIC) Calle 526 1499-1579, B1906APM Tolosa, Buenos Aires, Argentina
| | - Silvia S Rodríguez
- Electrophysiology Laboratory, Multidisciplinary Institute of Cell Biology (IMBICE), Universidad Nacional de La Plata - Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, and Comisión de Investigaciones de la Provincia de buenos Aires (CIC) Calle 526 1499-1579, B1906APM Tolosa, Buenos Aires, Argentina
| | - Diane Lipscombe
- Department of Neuroscience, Brown University; Sidney E. Frank Hall for Life Sciences, 185 Meeting Street, Providence, Rhode Island 02912, USA
| | - Jesica Raingo
- Electrophysiology Laboratory, Multidisciplinary Institute of Cell Biology (IMBICE), Universidad Nacional de La Plata - Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, and Comisión de Investigaciones de la Provincia de buenos Aires (CIC) Calle 526 1499-1579, B1906APM Tolosa, Buenos Aires, Argentina
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8
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Findeisen F, Campiglio M, Jo H, Abderemane-Ali F, Rumpf CH, Pope L, Rossen ND, Flucher BE, DeGrado WF, Minor DL. Stapled Voltage-Gated Calcium Channel (Ca V) α-Interaction Domain (AID) Peptides Act As Selective Protein-Protein Interaction Inhibitors of Ca V Function. ACS Chem Neurosci 2017; 8:1313-1326. [PMID: 28278376 PMCID: PMC5481814 DOI: 10.1021/acschemneuro.6b00454] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
![]()
For many voltage-gated
ion channels (VGICs), creation of a properly functioning ion channel
requires the formation of specific protein–protein interactions
between the transmembrane pore-forming subunits and cystoplasmic accessory
subunits. Despite the importance of such protein–protein interactions
in VGIC function and assembly, their potential as sites for VGIC modulator
development has been largely overlooked. Here, we develop meta-xylyl (m-xylyl) stapled peptides that
target a prototypic VGIC high affinity protein–protein interaction,
the interaction between the voltage-gated calcium channel (CaV) pore-forming subunit α-interaction domain (AID) and
cytoplasmic β-subunit (CaVβ). We show using
circular dichroism spectroscopy, X-ray crystallography, and isothermal
titration calorimetry that the m-xylyl staples enhance
AID helix formation are structurally compatible with native-like AID:CaVβ interactions and reduce the entropic penalty associated
with AID binding to CaVβ. Importantly, electrophysiological
studies reveal that stapled AID peptides act as effective inhibitors
of the CaVα1:CaVβ interaction
that modulate CaV function in an CaVβ
isoform-selective manner. Together, our studies provide a proof-of-concept
demonstration of the use of protein–protein interaction inhibitors
to control VGIC function and point to strategies for improved AID-based
CaV modulator design.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | - Daniel L. Minor
- Molecular Biophysics & Integrated Imaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
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9
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Lu JM, Liu DD, Li ZY, Ling C, Mei YA. Neuritin Enhances Synaptic Transmission in Medial Prefrontal Cortex in Mice by Increasing CaV3.3 Surface Expression. Cereb Cortex 2017; 27:3842-3855. [DOI: 10.1093/cercor/bhx082] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 03/23/2017] [Indexed: 02/02/2023] Open
Affiliation(s)
- Jun-Mei Lu
- State Key Laboratory of Medical Neurobiology and School of Life Sciences, Institutes of Brain Science, Fudan University, Shanghai 200433, China
| | - Dong-Dong Liu
- State Key Laboratory of Medical Neurobiology and School of Life Sciences, Institutes of Brain Science, Fudan University, Shanghai 200433, China
| | - Zhao-Yang Li
- State Key Laboratory of Medical Neurobiology and School of Life Sciences, Institutes of Brain Science, Fudan University, Shanghai 200433, China
| | - Chen Ling
- State Key Laboratory of Genetic Engineering, School of Life Sciences, Zhongshan Hospital, Fudan University, Shanghai 200032, China
| | - Yan-Ai Mei
- State Key Laboratory of Medical Neurobiology and School of Life Sciences, Institutes of Brain Science, Fudan University, Shanghai 200433, China
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10
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Trafficking of neuronal calcium channels. Neuronal Signal 2017; 1:NS20160003. [PMID: 32714572 PMCID: PMC7373241 DOI: 10.1042/ns20160003] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2017] [Revised: 01/20/2017] [Accepted: 01/19/2017] [Indexed: 12/18/2022] Open
Abstract
Neuronal voltage-gated calcium channels (VGCCs) serve complex yet essential physiological functions via their pivotal role in translating electrical signals into intracellular calcium elevations and associated downstream signalling pathways. There are a number of regulatory mechanisms to ensure a dynamic control of the number of channels embedded in the plasma membrane, whereas alteration of the surface expression of VGCCs has been linked to various disease conditions. Here, we provide an overview of the mechanisms that control the trafficking of VGCCs to and from the plasma membrane, and discuss their implication in pathophysiological conditions and their potential as therapeutic targets.
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11
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Page KM, Rothwell SW, Dolphin AC. The CaVβ Subunit Protects the I-II Loop of the Voltage-gated Calcium Channel CaV2.2 from Proteasomal Degradation but Not Oligoubiquitination. J Biol Chem 2016; 291:20402-16. [PMID: 27489103 PMCID: PMC5034038 DOI: 10.1074/jbc.m116.737270] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Indexed: 11/06/2022] Open
Abstract
CaVβ subunits interact with the voltage-gated calcium channel CaV2.2 on a site in the intracellular loop between domains I and II (the I-II loop). This interaction influences the biophysical properties of the channel and leads to an increase in its trafficking to the plasma membrane. We have shown previously that a mutant CaV2.2 channel that is unable to bind CaVβ subunits (CaV2.2 W391A) was rapidly degraded (Waithe, D., Ferron, L., Page, K. M., Chaggar, K., and Dolphin, A. C. (2011) J. Biol. Chem. 286, 9598-9611). Here we show that, in the absence of CaVβ subunits, a construct consisting of the I-II loop of CaV2.2 was directly ubiquitinated and degraded by the proteasome system. Ubiquitination could be prevented by mutation of all 12 lysine residues in the I-II loop to arginines. Including a palmitoylation motif at the N terminus of CaV2.2 I-II loop was insufficient to target it to the plasma membrane in the absence of CaVβ subunits even when proteasomal degradation was inhibited with MG132 or ubiquitination was prevented by the lysine-to-arginine mutations. In the presence of CaVβ subunit, the palmitoylated CaV2.2 I-II loop was protected from degradation, although oligoubiquitination could still occur, and was efficiently trafficked to the plasma membrane. We propose that targeting to the plasma membrane requires a conformational change in the I-II loop that is induced by binding of the CaVβ subunit.
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Affiliation(s)
- Karen M Page
- From the Department of Neuroscience, Physiology and Pharmacology, University College London, Gower St., London WC1E 6BT, United Kingdom
| | - Simon W Rothwell
- From the Department of Neuroscience, Physiology and Pharmacology, University College London, Gower St., London WC1E 6BT, United Kingdom
| | - Annette C Dolphin
- From the Department of Neuroscience, Physiology and Pharmacology, University College London, Gower St., London WC1E 6BT, United Kingdom
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12
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Growth differentiation factor-15 promotes glutamate release in medial prefrontal cortex of mice through upregulation of T-type calcium channels. Sci Rep 2016; 6:28653. [PMID: 27353765 PMCID: PMC4926092 DOI: 10.1038/srep28653] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Accepted: 06/07/2016] [Indexed: 01/01/2023] Open
Abstract
Growth differentiation factor-15 (GDF-15) has been implicated in ischemic brain injury and synapse development, but its involvement in modulating neuronal excitability and synaptic transmission remain poorly understood. In this study, we investigated the effects of GDF-15 on non-evoked miniature excitatory post-synaptic currents (mEPSCs) and neurotransmitter release in the medial prefrontal cortex (mPFC) in mice. Incubation of mPFC slices with GDF-15 for 60 min significantly increased the frequency of mEPSCs without effect on their amplitude. GDF-15 also significantly elevated presynaptic glutamate release, as shown by HPLC. These effects were blocked by dual TGF-β type I receptor (TβRI) and TGF-β type II receptor (TβRII) antagonists, but not by a TβRI antagonist alone. Meanwhile, GDF-15 enhanced pERK level, and inhibition of MAPK/ERK activity attenuated the GDF-15-induced increases in mEPSC and glutamate release. Blocking T-type calcium channels reduced the GDF-15 induced up-regulation of synaptic transmission. Membrane-protein extraction and use of an intracellular protein-transport inhibitor showed that GDF-15 promoted CaV3.1 and CaV3.3 α-subunit expression by trafficking to the membrane. These results confirm previous findings in cerebellar granule neurons, in which GDF-15 induces its neurobiological effects via TβRII and activation of the ERK pathway, providing novel insights into the mechanism of GDF-15 function in cortical neurons.
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13
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Lainé V, Ségor JR, Zhan H, Bessereau JL, Jospin M. Hyperactivation of L-type voltage-gated Ca2+ channels in Caenorhabditis elegans striated muscle can result from point mutations in the IS6 or the IIIS4 segment of the α1 subunit. ACTA ACUST UNITED AC 2014; 217:3805-14. [PMID: 25214488 DOI: 10.1242/jeb.106732] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Several human diseases, including hypokalemic periodic paralysis and Timothy syndrome, are caused by mutations in voltage-gated calcium channels. The effects of these mutations are not always well understood, partially because of difficulties in expressing these channels in heterologous systems. The use of Caenorhabditis elegans could be an alternative approach to determine the effects of mutations on voltage-gated calcium channel function because all the main types of voltage-gated calcium channels are found in C. elegans, a large panel of mutations already exists and efficient genetic tools are available to engineer customized mutations in any gene. In this study, we characterize the effects of two gain-of-function mutations in egl-19, which encodes the L-type calcium channel α1 subunit. One of these mutations, ad695, leads to the replacement of a hydrophobic residue in the IIIS4 segment. The other mutation, n2368, changes a conserved glycine of IS6 segment; this mutation has been identified in patients with Timothy syndrome. We show that both egl-19 (gain-of-function) mutants have defects in locomotion and morphology that are linked to higher muscle tone. Using in situ electrophysiological approaches in striated muscle cells, we provide evidence that this high muscle tone is due to a shift of the voltage dependency towards negative potentials, associated with a decrease of the inactivation rate of the L-type Ca(2+) current. Moreover, we show that the maximal conductance of the Ca(2+) current is decreased in the strongest mutant egl-19(n2368), and that this decrease is correlated with a mislocalization of the channel.
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Affiliation(s)
- Viviane Lainé
- CNRS, UMR 5534, Université Lyon 1, Villeurbanne, F-69622, France
| | - Jean Rony Ségor
- CNRS, UMR 5534, Université Lyon 1, Villeurbanne, F-69622, France
| | - Hong Zhan
- CNRS, UMR 5534, Université Lyon 1, Villeurbanne, F-69622, France
| | | | - Maelle Jospin
- CNRS, UMR 5534, Université Lyon 1, Villeurbanne, F-69622, France
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14
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Dawson TF, Boone AN, Senatore A, Piticaru J, Thiyagalingam S, Jackson D, Davison A, Spafford JD. Gene splicing of an invertebrate beta subunit (LCavβ) in the N-terminal and HOOK domains and its regulation of LCav1 and LCav2 calcium channels. PLoS One 2014; 9:e92941. [PMID: 24690951 PMCID: PMC3972191 DOI: 10.1371/journal.pone.0092941] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Accepted: 02/27/2014] [Indexed: 01/31/2023] Open
Abstract
The accessory beta subunit (Ca(v)β) of calcium channels first appear in the same genome as Ca(v)1 L-type calcium channels in single-celled coanoflagellates. The complexity of this relationship expanded in vertebrates to include four different possible Ca(v)β subunits (β1, β2, β3, β4) which associate with four Ca(v)1 channel isoforms (Ca(v)1.1 to Ca(v)1.4) and three Ca(v)2 channel isoforms (Ca(v)2.1 to Ca(v)2.3). Here we assess the fundamentally-shared features of the Ca(v)β subunit in an invertebrate model (pond snail Lymnaea stagnalis) that bears only three homologous genes: (LCa(v)1, LCa(v)2, and LCa(v)β). Invertebrate Ca(v)β subunits (in flatworms, snails, squid and honeybees) slow the inactivation kinetics of Ca(v)2 channels, and they do so with variable N-termini and lacking the canonical palmitoylation residues of the vertebrate β2a subunit. Alternative splicing of exon 7 of the HOOK domain is a primary determinant of a slow inactivation kinetics imparted by the invertebrate LCa(v)β subunit. LCa(v)β will also slow the inactivation kinetics of LCa(v)3 T-type channels, but this is likely not physiologically relevant in vivo. Variable N-termini have little influence on the voltage-dependent inactivation kinetics of differing invertebrate Ca(v)β subunits, but the expression pattern of N-terminal splice isoforms appears to be highly tissue specific. Molluscan LCa(v)β subunits have an N-terminal "A" isoform (coded by exons: 1a and 1b) that structurally resembles the muscle specific variant of vertebrate β1a subunit, and has a broad mRNA expression profile in brain, heart, muscle and glands. A more variable "B" N-terminus (exon 2) in the exon position of mammalian β3 and has a more brain-centric mRNA expression pattern. Lastly, we suggest that the facilitation of closed-state inactivation (e.g. observed in Ca(v)2.2 and Ca(v)β3 subunit combinations) is a specialization in vertebrates, because neither snail subunit (LCa(v)2 nor LCa(v)β) appears to be compatible with this observed property.
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Affiliation(s)
- Taylor F. Dawson
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
| | - Adrienne N. Boone
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
| | - Adriano Senatore
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
| | - Joshua Piticaru
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
| | | | - Daniel Jackson
- Institute of Genetics, School of Biology, University of Nottingham, Nottingham, United Kingdom
| | - Angus Davison
- Institute of Genetics, School of Biology, University of Nottingham, Nottingham, United Kingdom
| | - J. David Spafford
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
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15
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Senatore A, Guan W, Spafford JD. Cav3 T-type channels: regulators for gating, membrane expression, and cation selectivity. Pflugers Arch 2014; 466:645-60. [PMID: 24515291 DOI: 10.1007/s00424-014-1449-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2013] [Revised: 01/10/2014] [Accepted: 01/12/2014] [Indexed: 12/13/2022]
Abstract
Cav3 T-type channels are low-voltage-gated channels with rapid kinetics that are classified among the calcium-selective Cav1 and Cav2 type channels. Here, we outline the fundamental and unique regulators of T-type channels. An ubiquitous and proximally located "gating brake" works in concert with the voltage-sensor domain and S6 alpha-helical segment from domain II to set the canonical low-threshold and transient gating features of T-type channels. Gene splicing of optional exon 25c (and/or exon 26) in the short III-IV linker provides a developmental switch between modes of activity, such as activating in response to membrane depolarization, to channels requiring hyperpolarization input before being available to activate. Downstream of the gating brake in the I-II linker is a key region for regulating channel expression where alternative splicing patterns correlate with functional diversity of spike patterns, pacemaking rate (especially in the heart), stage of development, and animal size. A small but persistent window conductance depolarizes cells and boosts excitability at rest. T-type channels possess an ion selectivity that can resemble not only the calcium ion exclusive Cav1 and Cav2 channels but also the sodium ion selectivity of Nav1 sodium channels too. Alternative splicing in the extracellular turret of domain II generates highly sodium-permeable channels, which contribute to low-threshold sodium spikes. Cav3 channels are more ubiquitous among multicellular animals and more widespread in tissues than the more brain centric Nav1 sodium channels in invertebrates. Highly sodium-permeant Cav3 channels can functionally replace Nav1 channels in species where they are lacking, such as in Caenorhabditis elegans.
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Affiliation(s)
- A Senatore
- Department of Biology, University of Waterloo, B1-173, Waterloo, ON, N2L 3G1, Canada
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16
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Almagor L, Avinery R, Hirsch JA, Beck R. Structural flexibility of CaV1.2 and CaV2.2 I-II proximal linker fragments in solution. Biophys J 2014; 104:2392-400. [PMID: 23746511 DOI: 10.1016/j.bpj.2013.04.034] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Revised: 04/15/2013] [Accepted: 04/18/2013] [Indexed: 12/22/2022] Open
Abstract
Voltage-dependent calcium channels (CaV) enable the inward flow of calcium currents for a wide range of cells. CaV1 and CaV2 subtype α1 subunits form the conducting pore using four repeated membrane domains connected by intracellular linkers. The domain I-II linker connects to the membrane gate (IS6), forming an α-helix, and is bound to the CaVβ subunit. Previous studies indicated that this region may or may not form a continuous helix depending on the CaV subtype, thereby modulating channel activation and inactivation properties. Here, we used small-angle x-ray scattering and ensemble modeling analysis to investigate the solution structure of these linkers, extending from the membrane domain and including the CaVβ-binding site, called the proximal linker (PL). The results demonstrate that the CaV1.2 PL is more flexible than the CaV2.2 PL, the flexibility is intrinsic and not dependent on CaVβ binding, and the flexibility can be most easily explained by the presence of conserved glycines. Our analysis also provides a robust example of investigating protein domains in which flexibility plays an essential role.
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Affiliation(s)
- Lior Almagor
- Department of Biochemistry and Molecular Biology, Institute of Structure Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
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17
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Perez-Reyes E, Lee JH. Ins and outs of T-channel structure function. Pflugers Arch 2013; 466:627-33. [PMID: 24337909 DOI: 10.1007/s00424-013-1419-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Accepted: 12/03/2013] [Indexed: 02/07/2023]
Abstract
We review the ins and outs of T-channel structure, focusing on the extracellular high-affinity metal-binding site and intracellular loops. The high-affinity metal-binding site was localized to repeat I of Cav3.2. Interestingly, a similar binding site was found in the high voltage-activated Cav2.3 channel where it controls the channels' voltage dependence. Histidine at position 191 has a particularly interesting role in the high-affinity binding site, and its modification plays an important role in channel regulation by pharmacological agents that alter redox reactions. The intracellular loop connecting repeats I and II plays two important roles in Cav3.2 properties: one, its gating; and two, its surface expression. These studies have also identified a highly conserved intracellular gating brake that is predicted to form a helix-loop-helix structure. We conclude that the gating brake establishes important contacts with the gating machinery, thereby stabilizing a closed state of T-channels. This interaction is disrupted by depolarization, allowing the S6 segments to open and allowing Ca(2+) ions to flow through. Studies in cultured hippocampal neurons provided novel insights into how mutations found in idiopathic generalized epilepsy patients increase seizure susceptibility by both altering T-current pacemaker currents and by activating Ca-activated transcription factors that regulate dendritic arborization. These studies reveal novel roles for T-channels to control cellular physiology.
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Affiliation(s)
- Edward Perez-Reyes
- Department of Pharmacology, University of Virginia, Charlottesville, VA, USA,
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18
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Eckle VS, Shcheglovitov A, Vitko I, Dey D, Yap CC, Winckler B, Perez-Reyes E. Mechanisms by which a CACNA1H mutation in epilepsy patients increases seizure susceptibility. J Physiol 2013; 592:795-809. [PMID: 24277868 DOI: 10.1113/jphysiol.2013.264176] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
T-type calcium channels play essential roles in regulating neuronal excitability and network oscillations in the brain. Mutations in the gene encoding Cav3.2 T-type Ca(2+) channels, CACNA1H, have been found in association with various forms of idiopathic generalized epilepsy. We and others have found that these mutations may influence neuronal excitability either by altering the biophysical properties of the channels or by increasing their surface expression. The goals of the present study were to investigate the excitability of neurons expressing Cav3.2 with the epilepsy mutation, C456S, and to elucidate the mechanisms by which it influences neuronal properties. We found that expression of the recombinant C456S channels substantially increased the excitability of cultured neurons by increasing the spontaneous firing rate and reducing the threshold for rebound burst firing. Additionally, we found that molecular determinants in the I-II loop (the region in which most childhood absence epilepsy-associated mutations are found) substantially increase the surface expression of T-channels but do not alter the relative distribution of channels into dendrites of cultured hippocampal neurons. Finally, we discovered that expression of C456S channels promoted dendritic growth and arborization. These effects were reversed to normal by either the absence epilepsy drug ethosuximide or a novel T-channel blocker, TTA-P2. As Ca(2+)-regulated transcription factors also increase dendritic development, we tested a transactivator trap assay and found that the C456S variant can induce changes in gene transcription. Taken together, our findings suggest that gain-of-function mutations in Cav3.2 T-type Ca(2+) channels increase seizure susceptibility by directly altering neuronal electrical properties and indirectly by changing gene expression.
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Affiliation(s)
- Veit-Simon Eckle
- Jordan Hall 800735, 1340 Jefferson Park Avenue, Charlottesville, VA 22908, USA.
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19
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Venom peptides as a rich source of cav2.2 channel blockers. Toxins (Basel) 2013; 5:286-314. [PMID: 23381143 PMCID: PMC3640536 DOI: 10.3390/toxins5020286] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Revised: 01/07/2013] [Accepted: 01/25/2013] [Indexed: 11/24/2022] Open
Abstract
Cav2.2 is a calcium channel subtype localized at nerve terminals, including nociceptive fibers, where it initiates neurotransmitter release. Cav2.2 is an important contributor to synaptic transmission in ascending pain pathways, and is up-regulated in the spinal cord in chronic pain states along with the auxiliary α2δ1 subunit. It is therefore not surprising that toxins that inhibit Cav2.2 are analgesic. Venomous animals, such as cone snails, spiders, snakes, assassin bugs, centipedes and scorpions are rich sources of remarkably potent and selective Cav2.2 inhibitors. However, side effects in humans currently limit their clinical use. Here we review Cav2.2 inhibitors from venoms and their potential as drug leads.
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20
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Zamponi GW, Currie KPM. Regulation of Ca(V)2 calcium channels by G protein coupled receptors. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:1629-43. [PMID: 23063655 DOI: 10.1016/j.bbamem.2012.10.004] [Citation(s) in RCA: 141] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Revised: 10/02/2012] [Accepted: 10/04/2012] [Indexed: 12/29/2022]
Abstract
Voltage gated calcium channels (Ca²⁺ channels) are key mediators of depolarization induced calcium influx into excitable cells, and thereby play pivotal roles in a wide array of physiological responses. This review focuses on the inhibition of Ca(V)2 (N- and P/Q-type) Ca²⁺-channels by G protein coupled receptors (GPCRs), which exerts important autocrine/paracrine control over synaptic transmission and neuroendocrine secretion. Voltage-dependent inhibition is the most widespread mechanism, and involves direct binding of the G protein βγ dimer (Gβγ) to the α1 subunit of Ca(V)2 channels. GPCRs can also recruit several other distinct mechanisms including phosphorylation, lipid signaling pathways, and channel trafficking that result in voltage-independent inhibition. Current knowledge of Gβγ-mediated inhibition is reviewed, including the molecular interactions involved, determinants of voltage-dependence, and crosstalk with other cell signaling pathways. A summary of recent developments in understanding the voltage-independent mechanisms prominent in sympathetic and sensory neurons is also included. This article is part of a Special Issue entitled: Calcium channels.
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Affiliation(s)
- Gerald W Zamponi
- Department of Physiology & Pharmacology, Hotchkiss Brain Institute, University of Calgary, Canada
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21
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Buraei Z, Yang J. Structure and function of the β subunit of voltage-gated Ca²⁺ channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:1530-40. [PMID: 22981275 DOI: 10.1016/j.bbamem.2012.08.028] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Revised: 08/22/2012] [Accepted: 08/25/2012] [Indexed: 12/31/2022]
Abstract
The voltage-gated Ca²⁺ channel β subunit (Ca(v)β) is a cytosolic auxiliary subunit that plays an essential role in regulating the surface expression and gating properties of high-voltage activated (HVA) Ca²⁺ channels. It is also crucial for the modulation of HVA Ca²⁺ channels by G proteins, kinases, Ras-related RGK GTPases, and other proteins. There are indications that Ca(v)β may carry out Ca²⁺ channel-independent functions. Ca(v)β knockouts are either non-viable or result in a severe pathophysiology, and mutations in Ca(v)β have been implicated in disease. In this article, we review the structure and various biological functions of Ca(v)β, as well as recent advances. This article is part of a Special Issue entitled: Calcium channels.
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Affiliation(s)
- Zafir Buraei
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
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22
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The role of a voltage-dependent Ca2+ channel intracellular linker: a structure-function analysis. J Neurosci 2012; 32:7602-13. [PMID: 22649239 DOI: 10.1523/jneurosci.5727-11.2012] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Voltage-dependent calcium channels (VDCCs) allow the passage of Ca(2+) ions through cellular membranes in response to membrane depolarization. The channel pore-forming subunit, α1, and a regulatory subunit (Ca(V)β) form a high affinity complex where Ca(V)β binds to a α1 interacting domain in the intracellular linker between α1 membrane domains I and II (I-II linker). We determined crystal structures of Ca(V)β2 functional core in complex with the Ca(V)1.2 and Ca(V)2.2 I-II linkers to a resolution of 1.95 and 2.0 Å, respectively. Structural differences between the highly conserved linkers, important for coupling Ca(V)β to the channel pore, guided mechanistic functional studies. Electrophysiological measurements point to the importance of differing linker structure in both Ca(V)1 and 2 subtypes with mutations affecting both voltage- and calcium-dependent inactivation and voltage dependence of activation. These linker effects persist in the absence of Ca(V)β, pointing to the intrinsic role of the linker in VDCC function and suggesting that I-II linker structure can serve as a brake during inactivation.
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23
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Mor M, Beharier O, Levy S, Kahn J, Dror S, Blumenthal D, Gheber LA, Peretz A, Katz A, Moran A, Etzion Y. ZnT-1 enhances the activity and surface expression of T-type calcium channels through activation of Ras-ERK signaling. Am J Physiol Cell Physiol 2012; 303:C192-203. [DOI: 10.1152/ajpcell.00427.2011] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Zinc transporter-1 (ZnT-1) is a putative zinc transporter that confers cellular resistance from zinc toxicity. In addition, ZnT-1 has important regulatory functions, including inhibition of L-type calcium channels and activation of Raf-1 kinase. Here we studied the effects of ZnT-1 on the expression and function of T-type calcium channels. In Xenopus oocytes expressing voltage-gated calcium channel (CaV) 3.1 or CaV3.2, ZnT-1 enhanced the low-threshold calcium currents ( IcaT) to 182 ± 15 and 167.95 ± 9.27% of control, respectively ( P < 0.005 for both channels). As expected, ZnT-1 also enhanced ERK phosphorylation. Coexpression of ZnT-1 and nonactive Raf-1 blocked the ZnT-1-mediated ERK phosphorylation and abolished the ZnT-1-induced augmentation of IcaT. In mammalian cells (Chinese hamster ovary), coexpression of CaV3.1 and ZnT-1 increased the IcaT to 166.37 ± 6.37% compared with cells expressing CaV3.1 alone ( P < 0.01). Interestingly, surface expression measurements using biotinylation or total internal reflection fluorescence microscopy indicated marked ZnT-1-induced enhancement of CaV3.1 surface expression. The MEK inhibitor PD-98059 abolished the ZnT-1-induced augmentation of surface expression of CaV3.1. In cultured murine cardiomyocytes (HL-1 cells), transient exposure to zinc, leading to enhanced ZnT-1 expression, also enhanced the surface expression of endogenous CaV3.1 channels. Consistently, in these cells, endothelin-1, a potent activator of Ras-ERK signaling, enhanced the surface expression of CaV3.1 channels in a PD-98059-sensitive manner. Our findings indicate that ZnT-1 enhances the activity of CaV3.1 and CaV3.2 through activation of Ras-ERK signaling. The augmentation of CaV3.1 currents by Ras-ERK activation is associated with enhanced trafficking of the channel to the plasma membrane.
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Affiliation(s)
- Merav Mor
- Department of Physiology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Cardiac Arrhythmia Research Laboratory, Soroka University Medical Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Ofer Beharier
- Department of Physiology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Cardiac Arrhythmia Research Laboratory, Soroka University Medical Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Shiri Levy
- Department of Physiology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Joy Kahn
- Department of Physiology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Shani Dror
- Department of Physiology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
- Cardiac Arrhythmia Research Laboratory, Soroka University Medical Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Daniel Blumenthal
- Department of Biotechnology Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Levi A. Gheber
- Department of Biotechnology Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Asher Peretz
- Department of Physiology and Pharmacology, Sackler Medical School, Tel Aviv University, Tel Aviv, Israel
| | - Amos Katz
- Department of Cardiology, Barzilai Medical Center, Ashkelon, Israel; and
- Cardiac Arrhythmia Research Laboratory, Soroka University Medical Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Arie Moran
- Department of Physiology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Yoram Etzion
- Cardiac Arrhythmia Research Laboratory, Soroka University Medical Center and Ben-Gurion University of the Negev, Beer-Sheva, Israel
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24
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Bagriantsev SN, Clark KA, Minor DL. Metabolic and thermal stimuli control K(2P)2.1 (TREK-1) through modular sensory and gating domains. EMBO J 2012; 31:3297-308. [PMID: 22728824 PMCID: PMC3411076 DOI: 10.1038/emboj.2012.171] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Accepted: 05/25/2012] [Indexed: 01/01/2023] Open
Abstract
The two-pore domain potassium channel K2P2.1 (TREK-1) responds to extracellular and intracellular stimuli, including pH and temperature. This study elucidates how the intracellular sensor element relays metabolic and thermal stimuli to the extracellular C-type gating element. K2P2.1 (TREK-1) is a polymodal two-pore domain leak potassium channel that responds to external pH, GPCR-mediated phosphorylation signals, and temperature through the action of distinct sensors within the channel. How the various intracellular and extracellular sensory elements control channel function remains unresolved. Here, we show that the K2P2.1 (TREK-1) intracellular C-terminal tail (Ct), a major sensory element of the channel, perceives metabolic and thermal commands and relays them to the extracellular C-type gate through transmembrane helix M4 and pore helix 1. By decoupling Ct from the pore-forming core, we further demonstrate that Ct is the primary heat-sensing element of the channel, whereas, in contrast, the pore domain lacks robust temperature sensitivity. Together, our findings outline a mechanism for signal transduction within K2P2.1 (TREK-1) in which there is a clear crosstalk between the C-type gate and intracellular Ct domain. In addition, our findings support the general notion of the existence of modular temperature-sensing domains in temperature-sensitive ion channels. This marked distinction between gating and sensory elements suggests a general design principle that may underlie the function of a variety of temperature-sensitive channels.
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25
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Fang K, Colecraft HM. Mechanism of auxiliary β-subunit-mediated membrane targeting of L-type (Ca(V)1.2) channels. J Physiol 2011; 589:4437-55. [PMID: 21746784 DOI: 10.1113/jphysiol.2011.214247] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Ca(2+) influx via Ca(V)1/Ca(V)2 channels drives processes ranging from neurotransmission to muscle contraction. Association of a pore-forming α(1) and cytosolic β is necessary for trafficking Ca(V)1/Ca(V)2 channels to the cell surface through poorly understood mechanisms. A prevalent idea suggests β binds the α(1) intracellular I-II loop, masking an endoplasmic reticulum (ER) retention signal as the dominant mechanism for Ca(V)1/Ca(V)2 channel membrane trafficking. There are hints that other α(1) subunit cytoplasmic domains may play a significant role, but the nature of their potential contribution is unclear. We assessed the roles of all intracellular domains of Ca(V)1.2-α(1C) by generating chimeras featuring substitutions of all possible permutations of intracellular loops/termini of α(1C) into the β-independent Ca(V)3.1-α(1G) channel. Surprisingly, functional analyses demonstrated α(1C) I-II loop strongly increases channel surface density while other cytoplasmic domains had a competing opposing effect. Alanine-scanning mutagenesis identified an acidic-residue putative ER export motif responsible for the I-II loop-mediated increase in channel surface density. β-dependent increase in current arose as an emergent property requiring four α(1C) intracellular domains, with the I-II loop and C-terminus being essential. The results suggest β binding to the α(1C) I-II loop causes a C-terminus-dependent rearrangement of intracellular domains, shifting a balance of power between export signals on the I-II loop and retention signals elsewhere.
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Affiliation(s)
- Kun Fang
- Department of Physiology and Cellular Biophysics, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA
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26
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Minor DL, Findeisen F. Progress in the structural understanding of voltage-gated calcium channel (CaV) function and modulation. Channels (Austin) 2011; 4:459-74. [PMID: 21139419 DOI: 10.4161/chan.4.6.12867] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Voltage-gated calcium channels (CaVs) are large, transmembrane multiprotein complexes that couple membrane depolarization to cellular calcium entry. These channels are central to cardiac action potential propagation, neurotransmitter and hormone release, muscle contraction, and calcium-dependent gene transcription. Over the past six years, the advent of high-resolution structural studies of CaV components from different isoforms and CaV modulators has begun to reveal the architecture that underlies the exceptionally rich feedback modulation that controls CaV action. These descriptions of CaV molecular anatomy have provided new, structure-based insights into the mechanisms by which particular channel elements affect voltage-dependent inactivation (VDI), calcium‑dependent inactivation (CDI), and calcium‑dependent facilitation (CDF). The initial successes have been achieved through structural studies of soluble channel domains and modulator proteins and have proven most powerful when paired with biochemical and functional studies that validate ideas inspired by the structures. Here, we review the progress in this growing area and highlight some key open challenges for future efforts.
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Affiliation(s)
- Daniel L Minor
- Cardiovascular Research Institute, University of California-San Francisco, CA, USA.
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Karmažínová M, Baumgart JP, Perez-Reyes E, Lacinová L. The voltage dependence of gating currents of the neuronal CA(v)3.3 channel is determined by the gating brake in the I-II loop. Pflugers Arch 2011; 461:461-8. [PMID: 21340458 DOI: 10.1007/s00424-011-0937-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2010] [Revised: 02/06/2011] [Accepted: 02/08/2011] [Indexed: 01/10/2023]
Abstract
Low-voltage-activated Ca(v)3 Ca(2+) channels have an activation threshold around -60 mV, which is lower than the activation threshold of other voltage-dependent calcium channels (VDCCs). The kinetics of their activation at membrane voltages just above the activation threshold is much slower than the activation kinetics of other VDCCs. It was demonstrated recently that the intracellular loop connecting repeats I and II of all three Ca(v)3 channels contains a so-called gating brake. Disruption of this brake yields channels that activate at even more hyperpolarized potentials with significantly accelerated kinetics. We have compared gating of a wild-type Ca(v)3.3 channel and a mutated ID12 channel, in which the putative gating brake at the proximal part of the I-II loop was removed. Voltage dependence of the gating current activation was shifted by 34.6 mV towards more hyperpolarized potentials in ID12 channel. ON-charge movement was significantly faster in the ID12 channel, while the kinetics of the off-charge was not altered by the mutation. We conclude that the putative gating brake in I-II loop hinders not only the opening of the conducting pore but also the activating movement of voltage-sensing S4 segments, stabilizing the channel in its closed state.
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Affiliation(s)
- Mária Karmažínová
- Institute of Molecular Physiology and Genetics, Centre of Excellence for Cardiovascular Research, Slovak Academy of Sciences, Bratislava, Slovakia
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28
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Abstract
Calcium regulates a wide spectrum of physiological processes such as heartbeat, muscle contraction, neuronal communication, hormone release, cell division, and gene transcription. Major entryways for Ca(2+) in excitable cells are high-voltage activated (HVA) Ca(2+) channels. These are plasma membrane proteins composed of several subunits, including α(1), α(2)δ, β, and γ. Although the principal α(1) subunit (Ca(v)α(1)) contains the channel pore, gating machinery and most drug binding sites, the cytosolic auxiliary β subunit (Ca(v)β) plays an essential role in regulating the surface expression and gating properties of HVA Ca(2+) channels. Ca(v)β is also crucial for the modulation of HVA Ca(2+) channels by G proteins, kinases, and the Ras-related RGK GTPases. New proteins have emerged in recent years that modulate HVA Ca(2+) channels by binding to Ca(v)β. There are also indications that Ca(v)β may carry out Ca(2+) channel-independent functions, including directly regulating gene transcription. All four subtypes of Ca(v)β, encoded by different genes, have a modular organization, consisting of three variable regions, a conserved guanylate kinase (GK) domain, and a conserved Src-homology 3 (SH3) domain, placing them into the membrane-associated guanylate kinase (MAGUK) protein family. Crystal structures of Ca(v)βs reveal how they interact with Ca(v)α(1), open new research avenues, and prompt new inquiries. In this article, we review the structure and various biological functions of Ca(v)β, with both a historical perspective as well as an emphasis on recent advances.
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Affiliation(s)
- Zafir Buraei
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
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29
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Perez-Reyes E. Characterization of the gating brake in the I-II loop of CaV3 T-type calcium channels. Channels (Austin) 2010; 4:453-8. [PMID: 21099341 DOI: 10.4161/chan.4.6.12889] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Our interest was drawn to the I-II loop of Cav3 channels for two reasons: one, transfer of the I-II loop from a high voltage-activated channel (Cav2.2) to a low voltage-activated channel (Cav3.1) unexpectedly produced an ultra-low voltage activated channel; and two, sequence variants of the I-II loop found in childhood absence epilepsy patients altered channel gating and increased surface expression of Cav3.2 channels. To determine the roles of this loop we have studied the structure of the loop and the biophysical consequences of altering its structure. Deletions localized the gating brake to the first 62 amino acids after IS6 in all three Cav3 channels, establishing the evolutionary conservation of this region and its function. Circular dichroism was performed on a purified fragment of the I-II loop from Cav3.2 to reveal a high α-helical content. De novo computer modeling predicted the gating brake formed a helix-loop-helix structure. This model was tested by replacing the helical regions with poly-proline-glycine (PGPGPG), which introduces kinks and flexibility. These mutations had profound effects on channel gating, shifting both steady-state activation and inactivation curves, as well as accelerating channel kinetics. Mutations designed to preserve the helical structure (poly-alanine, which forms α-helices) had more modest effects. Taken together, we conclude the second helix of the gating brake establishes important contacts with the gating machinery, thereby stabilizing a closed state of T-channels, and that this interaction is disrupted by depolarization, allowing the S6 segments to spread open and Ca (2+) ions to flow through.
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Affiliation(s)
- Edward Perez-Reyes
- Department of Pharmacology, University of Virginia, Charlottesville, VA, USA.
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30
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Abstract
Voltage-gated Ca(2+) channels translate the electrical inputs of excitable cells into biochemical outputs by controlling influx of the ubiquitous second messenger Ca(2+) . As such the channels play pivotal roles in many cellular functions including the triggering of neurotransmitter and hormone release by CaV2.1 (P/Q-type) and CaV2.2 (N-type) channels. It is well established that G protein coupled receptors (GPCRs) orchestrate precise regulation neurotransmitter and hormone release through inhibition of CaV2 channels. Although the GPCRs recruit a number of different pathways, perhaps the most prominent, and certainly most studied among these is the so-called voltage-dependent inhibition mediated by direct binding of Gβγ to the α1 subunit of CaV2 channels. This article will review the basics of Ca(2+) -channels and G protein signaling, and the functional impact of this now classical inhibitory mechanism on channel function. It will also provide an update on more recent developments in the field, both related to functional effects and crosstalk with other signaling pathways, and advances made toward understanding the molecular interactions that underlie binding of Gβγ to the channel and the voltage-dependence that is a signature characteristic of this mechanism.
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Affiliation(s)
- Kevin P M Currie
- Department of Anesthesiology, Pharmacology and Center for Molecular Neuroscience, Vanderbilt University School of Medicine, Nashville, TN, USA.
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31
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Bae J, Suh EJ, Lee C. Interaction of T-type calcium channel Ca(V)3.3 with the β-subunit. Mol Cells 2010; 30:185-91. [PMID: 20803093 DOI: 10.1007/s10059-010-0106-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2010] [Revised: 05/12/2010] [Accepted: 05/27/2010] [Indexed: 11/24/2022] Open
Abstract
The β-subunit of high-voltage-activated (HVA) calcium channels is essential for the regulation of expression and gating. On the other hand, various reports have suggested that β subunits play no role in the regulation of low-voltage-activated T-type channels. In addition there has been no clear demonstration of a physical interaction between the α-subunit of T-type channel with β-subunit. In this study, we systematically investigated the interaction between Ca(V)α and Ca(V)β. The four Ca(V)β isoforms were expressed in a bacterial system and purified into homogeneity, whereas the ten types of Ca(V)α alpha interaction domain (AID) peptides were chemically synthesized. All possible combinations of Ca(V)α and Ca(V)β were then tested for by in vitro immunoassays. We describe here the identification of a new interaction between Ca(V)3.3 and Ca(V)β proteins. This interaction is of low affinity compared to that between the AID of the HVA α-subunit and the alpha-binding pocket (ABP) site of the β-subunit. The AID peptide of HVA channel exerted no effect on the Ca(V)3.3-Ca(V)β interaction, thus demonstrating that another site not in the ABP of Ca(V)β protein played a role in binding with Ca(V)3.3. This is the first demonstration of an α-β subunit interaction in a T-type calcium channel.
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Affiliation(s)
- Jinhee Bae
- Life Sciences Division, Korea Institute of Science and Technology, Seoul, 136-791, Korea
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32
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Direct inhibition of P/Q-type voltage-gated Ca2+ channels by Gem does not require a direct Gem/Cavbeta interaction. Proc Natl Acad Sci U S A 2010; 107:14887-92. [PMID: 20679232 DOI: 10.1073/pnas.1007543107] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The Rem, Rem2, Rad, and Gem/Kir (RGK) family of small GTP-binding proteins potently inhibits high voltage-activated (HVA) Ca(2+) channels, providing a powerful means of modulating neural, endocrine, and muscle functions. The molecular mechanisms of this inhibition are controversial and remain largely unclear. RGK proteins associate directly with Ca(2+) channel beta subunits (Ca(v)beta), and this interaction is widely thought to be essential for their inhibitory action. In this study, we investigate the molecular underpinnings of Gem inhibition of P/Q-type Ca(2+) channels. We find that a purified Gem protein markedly and acutely suppresses P/Q channel activity in inside-out membrane patches, that this action requires Ca(v)beta but not the Gem/Ca(v)beta interaction, and that Gem coimmunoprecipitates with the P/Q channel alpha(1) subunit (Ca(v)alpha(1)) in a Ca(v)beta-independent manner. By constructing chimeras between P/Q channels and Gem-insensitive low voltage-activated T-type channels, we identify a region encompassing transmembrane segments S1, S2, and S3 in the second homologous repeat of Ca(v)alpha(1) critical for Gem inhibition. Exchanging this region between P/Q and T channel Ca(v)alpha(1) abolishes Gem inhibition of P/Q channels and confers Ca(v)beta-dependent Gem inhibition to a chimeric T channel that also carries the P/Q I-II loop (a cytoplasmic region of Ca(v)alpha(1) that binds Ca(v)beta). Our results challenge the prevailing view regarding the role of Ca(v)beta in RGK inhibition of high voltage-activated Ca(2+) channels and prompt a paradigm in which Gem directly binds and inhibits Ca(v)beta-primed Ca(v)alpha(1) on the plasma membrane.
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33
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Roberts-Crowley ML, Rittenhouse AR. Arachidonic acid inhibition of L-type calcium (CaV1.3b) channels varies with accessory CaVbeta subunits. ACTA ACUST UNITED AC 2010; 133:387-403. [PMID: 19332620 PMCID: PMC2699108 DOI: 10.1085/jgp.200810047] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Arachidonic acid (AA) inhibits the activity of several different voltage-gated Ca2+ channels by an unknown mechanism at an unknown site. The Ca2+ channel pore-forming subunit (CaVα1) is a candidate for the site of AA inhibition because T-type Ca2+ channels, which do not require accessory subunits for expression, are inhibited by AA. Here, we report the unanticipated role of accessory CaVβ subunits on the inhibition of CaV1.3b L-type (L-) current by AA. Whole cell Ba2+ currents were measured from recombinant channels expressed in human embryonic kidney 293 cells at a test potential of −10 mV from a holding potential of −90 mV. A one-minute exposure to 10 µM AA inhibited currents with β1b, β3, or β4 58, 51, or 44%, respectively, but with β2a only 31%. At a more depolarized holding potential of −60 mV, currents were inhibited to a lesser degree. These data are best explained by a simple model where AA stabilizes CaV1.3b in a deep closed-channel conformation, resulting in current inhibition. Consistent with this hypothesis, inhibition by AA occurred in the absence of test pulses, indicating that channels do not need to open to become inhibited. AA had no effect on the voltage dependence of holding potential–dependent inactivation or on recovery from inactivation regardless of CaVβ subunit. Unexpectedly, kinetic analysis revealed evidence for two populations of L-channels that exhibit willing and reluctant gating previously described for CaV2 channels. AA preferentially inhibited reluctant gating channels, revealing the accelerated kinetics of willing channels. Additionally, we discovered that the palmitoyl groups of β2a interfere with inhibition by AA. Our novel findings that the CaVβ subunit alters kinetic changes and magnitude of inhibition by AA suggest that CaVβ expression may regulate how AA modulates Ca2+-dependent processes that rely on L-channels, such as gene expression, enzyme activation, secretion, and membrane excitability.
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Affiliation(s)
- Mandy L Roberts-Crowley
- Department of Physiology and Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA 01655, USA
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34
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Zamponi GW, Lory P, Perez-Reyes E. Role of voltage-gated calcium channels in epilepsy. Pflugers Arch 2009; 460:395-403. [PMID: 20091047 DOI: 10.1007/s00424-009-0772-x] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2009] [Revised: 11/30/2009] [Accepted: 12/01/2009] [Indexed: 11/30/2022]
Abstract
It is well established that idiopathic generalized epilepsies (IGEs) show a polygenic origin and may arise from dysfunction of various types of voltage- and ligand-gated ion channels. There is an increasing body of literature implicating both high- and low-voltage-activated (HVA and LVA) calcium channels and their ancillary subunits in IGEs. Cav2.1 (P/Q-type) calcium channels control synaptic transmission at presynaptic nerve terminals, and mutations in the gene encoding the Cav2.1 alpha1 subunit (CACNA1A) have been linked to absence seizures in both humans and rodents. Similarly, mutations and loss of function mutations in ancillary HVA calcium channel subunits known to co-assemble with Cav2.1 result in IGE phenotypes in mice. It is important to note that in all these mouse models with mutations in HVA subunits, there is a compensatory increase in thalamic LVA currents which likely leads to the seizure phenotype. In fact, gain-of-function mutations have been identified in Cav3.2 (an LVA or T-type calcium channel encoded by the CACNA1H gene) in patients with congenital forms of IGEs, consistent with increased excitability of neurons as a result of enhanced T-type channel function. In this paper, we provide a broad overview of the roles of voltage-gated calcium channels, their mutations, and how they might contribute to the river that terminates in epilepsy.
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Affiliation(s)
- Gerald W Zamponi
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, T2N 4N1, Canada
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35
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Walsh CP, Davies A, Butcher AJ, Dolphin AC, Kitmitto A. Three-dimensional structure of CaV3.1: comparison with the cardiac L-type voltage-gated calcium channel monomer architecture. J Biol Chem 2009; 284:22310-22321. [PMID: 19520861 PMCID: PMC2755954 DOI: 10.1074/jbc.m109.017152] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calcium entry through voltage-gated calcium channels has widespread cellular effects upon a host of physiological processes including neuronal excitability, muscle excitation-contraction coupling, and secretion. Using single particle analysis methods, we have determined the first three-dimensional structure, at 23 A resolution, for a member of the low voltage-activated voltage-gated calcium channel family, CaV3.1, a T-type channel. CaV3.1 has dimensions of approximately 115x85x95 A, composed of two distinct segments. The cytoplasmic densities form a vestibule below the transmembrane domain with the C terminus, unambiguously identified by the presence of a His tag being approximately 65 A long and curling around the base of the structure. The cytoplasmic assembly has a large exposed surface area that may serve as a signaling hub with the C terminus acting as a "fishing rod" to bind regulatory proteins. We have also determined a three-dimensional structure, at a resolution of 25 A, for the monomeric form of the cardiac L-type voltage-gated calcium (high voltage-activated) channel with accessory proteins beta and alpha2delta bound to the ion channel polypeptide CaV1.2. Comparison with the skeletal muscle isoform finds a good match particularly with respect to the conformation, size, and shape of the domain identified as that formed by alpha2. Furthermore, modeling of the CaV3.1 structure (analogous to CaV1.2 at these resolutions) into the heteromeric L-type voltage-gated calcium channel complex volume reveals multiple interaction sites for beta-CaV1.2 binding and for the first time identifies the size and organization of the alpha2delta polypeptides.
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Affiliation(s)
- Conor P Walsh
- Cardiovascular Medicine, School of Clinical and Laboratory Sciences, Faculty of Medical and Human Sciences, University of Manchester, Manchester M13 9NT
| | - Anthony Davies
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Adrian J Butcher
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Annette C Dolphin
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Ashraf Kitmitto
- Cardiovascular Medicine, School of Clinical and Laboratory Sciences, Faculty of Medical and Human Sciences, University of Manchester, Manchester M13 9NT
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36
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Findeisen F, Minor DL. Disruption of the IS6-AID linker affects voltage-gated calcium channel inactivation and facilitation. ACTA ACUST UNITED AC 2009; 133:327-43. [PMID: 19237593 PMCID: PMC2654080 DOI: 10.1085/jgp.200810143] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Two processes dominate voltage-gated calcium channel (CaV) inactivation: voltage-dependent inactivation (VDI) and calcium-dependent inactivation (CDI). The CaVβ/CaVα1-I-II loop and Ca2+/calmodulin (CaM)/CaVα1–C-terminal tail complexes have been shown to modulate each, respectively. Nevertheless, how each complex couples to the pore and whether each affects inactivation independently have remained unresolved. Here, we demonstrate that the IS6–α-interaction domain (AID) linker provides a rigid connection between the pore and CaVβ/I-II loop complex by showing that IS6-AID linker polyglycine mutations accelerate CaV1.2 (L-type) and CaV2.1 (P/Q-type) VDI. Remarkably, mutations that either break the rigid IS6-AID linker connection or disrupt CaVβ/I-II association sharply decelerate CDI and reduce a second Ca2+/CaM/CaVα1–C-terminal–mediated process known as calcium-dependent facilitation. Collectively, the data strongly suggest that components traditionally associated solely with VDI, CaVβ and the IS6-AID linker, are essential for calcium-dependent modulation, and that both CaVβ-dependent and CaM-dependent components couple to the pore by a common mechanism requiring CaVβ and an intact IS6-AID linker.
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Affiliation(s)
- Felix Findeisen
- Cardiovascular Research Institute, Department of Biochemistry and Biophysics, California Institute for Quantitative Biosciences, University of California, San Francisco, CA 94158, USA
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37
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Zhang Y, Chen YH, Bangaru SD, He L, Abele K, Tanabe S, Kozasa T, Yang J. Origin of the voltage dependence of G-protein regulation of P/Q-type Ca2+ channels. J Neurosci 2008; 28:14176-88. [PMID: 19109500 PMCID: PMC2685181 DOI: 10.1523/jneurosci.1350-08.2008] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
G-protein (Gbetagamma)-mediated voltage-dependent inhibition of N- and P/Q-type Ca(2+) channels contributes to presynaptic inhibition and short-term synaptic plasticity. The voltage dependence derives from the dissociation of Gbetagamma from the inhibited channels, but the underlying molecular and biophysical mechanisms remain largely unclear. In this study we investigated the role in this process of Ca(2+) channel beta subunit (Ca(v)beta) and a rigid alpha-helical structure between the alpha-interacting domain (AID), the primary Ca(v)beta docking site on the channel alpha(1) subunit, and the pore-lining IS6 segment. Gbetagamma inhibition of P/Q-type channels was reconstituted in giant inside-out membrane patches from Xenopus oocytes. Large populations of channels devoid of Ca(v)beta were produced by washing out a mutant Ca(v)beta with a reduced affinity for the AID. These beta-less channels were still inhibited by Gbetagamma, but without any voltage dependence, indicating that Ca(v)beta is indispensable for voltage-dependent Gbetagamma inhibition. A truncated Ca(v)beta containing only the AID-binding guanylate kinase (GK) domain could fully confer voltage dependence to Gbetagamma inhibition. Gbetagamma did not alter inactivation properties, and channels recovered from Gbetagamma inhibition exhibited the same activation property as un-inhibited channels, indicating that Gbetagamma does not dislodge Ca(v)beta from the inhibited channel. Furthermore, voltage-dependent Gbetagamma inhibition was abolished when the rigid alpha-helix between the AID and IS6 was disrupted by insertion of multiple glycines, which also eliminated Ca(v)beta regulation of channel gating, revealing a pivotal role of this rigid alpha-helix in both processes. These results suggest that depolarization-triggered movement of IS6, coupled to the subsequent conformational change of the Gbetagamma-binding pocket through a rigid alpha-helix induced partly by the Ca(v)beta GK domain, causes the dissociation of Gbetagamma and is fundamental to voltage-dependent Gbetagamma inhibition.
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Affiliation(s)
- Yun Zhang
- 1Department of Biological Sciences, Columbia University, New York, New York 10027, and
| | - Yu-hang Chen
- 1Department of Biological Sciences, Columbia University, New York, New York 10027, and
| | - Saroja D. Bangaru
- 1Department of Biological Sciences, Columbia University, New York, New York 10027, and
| | - Linling He
- 1Department of Biological Sciences, Columbia University, New York, New York 10027, and
| | - Kathryn Abele
- 1Department of Biological Sciences, Columbia University, New York, New York 10027, and
| | - Shihori Tanabe
- 2Department of Pharmacology, University of Illinois College of Medicine, Chicago, Illinois 60612
| | - Tohru Kozasa
- 2Department of Pharmacology, University of Illinois College of Medicine, Chicago, Illinois 60612
| | - Jian Yang
- 1Department of Biological Sciences, Columbia University, New York, New York 10027, and
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Orientation of the calcium channel beta relative to the alpha(1)2.2 subunit is critical for its regulation of channel activity. PLoS One 2008; 3:e3560. [PMID: 18958281 PMCID: PMC2570331 DOI: 10.1371/journal.pone.0003560] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2008] [Accepted: 10/09/2008] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The Ca(v)beta subunits of high voltage-activated Ca(2+) channels control the trafficking and biophysical properties of the alpha(1) subunit. The Ca(v)beta-alpha(1) interaction site has been mapped by crystallographic studies. Nevertheless, how this interaction leads to channel regulation has not been determined. One hypothesis is that betas regulate channel gating by modulating movements of IS6. A key requirement for this direct-coupling model is that the linker connecting IS6 to the alpha-interaction domain (AID) be a rigid structure. METHODOLOGY/PRINCIPAL FINDINGS The present study tests this hypothesis by altering the flexibility and orientation of this region in alpha(1)2.2, then testing for Ca(v)beta regulation using whole cell patch clamp electrophysiology. Flexibility was induced by replacement of the middle six amino acids of the IS6-AID linker with glycine (PG6). This mutation abolished beta2a and beta3 subunits ability to shift the voltage dependence of activation and inactivation, and the ability of beta2a to produce non-inactivating currents. Orientation of Ca(v)beta with respect to alpha(1)2.2 was altered by deletion of 1, 2, or 3 amino acids from the IS6-AID linker (Bdel1, Bdel2, Bdel3, respectively). Again, the ability of Ca(v)beta subunits to regulate these biophysical properties were totally abolished in the Bdel1 and Bdel3 mutants. Functional regulation by Ca(v)beta subunits was rescued in the Bdel2 mutant, indicating that this part of the linker forms beta-sheet. The orientation of beta with respect to alpha was confirmed by the bimolecular fluorescence complementation assay. CONCLUSIONS/SIGNIFICANCE These results show that the orientation of the Ca(v)beta subunit relative to the alpha(1)2.2 subunit is critical, and suggests additional points of contact between these subunits are required for Ca(v)beta to regulate channel activity.
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39
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Shcheglovitov A, Vitko I, Bidaud I, Baumgart JP, Navarro-Gonzalez MF, Grayson TH, Lory P, Hill CE, Perez-Reyes E. Alternative splicing within the I-II loop controls surface expression of T-type Ca(v)3.1 calcium channels. FEBS Lett 2008; 582:3765-70. [PMID: 18930057 DOI: 10.1016/j.febslet.2008.10.013] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2008] [Revised: 10/03/2008] [Accepted: 10/06/2008] [Indexed: 11/30/2022]
Abstract
Molecular diversity of T-type/Ca(v)3 Ca2+ channels is created by expression of three genes and alternative splicing of those genes. Prompted by the important role of the I-II linker in gating and surface expression of Ca(v)3 channels, we describe here the properties of a novel variant that partially deletes this loop. The variant is abundantly expressed in rat brain, even exceeding transcripts with the complete exon 8. Electrophysiological analysis of the Delta8b variant revealed enhanced current density compared to Ca(v)3.1a, but similar gating. Luminometry experiments revealed an increase in the expression of Delta8b channels at the plasma membrane. We conclude that alternative splicing of Ca(v)3 channels regulates surface expression and may underlie disease states in which T-channel current density is increased.
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40
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Navarro-Gonzalez MF, Grayson TH, Meaney KR, Cribbs LL, Hill CE. Non-L-type voltage-dependent calcium channels control vascular tone of the rat basilar artery. Clin Exp Pharmacol Physiol 2008; 36:55-66. [PMID: 18759855 DOI: 10.1111/j.1440-1681.2008.05035.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
1. Constriction of cerebral arteries is considered to depend on L-type voltage-dependent calcium channels (VDCCs); however, many previous studies have used antagonists with potential non-selective actions. Our aim was to determine the expression and function of VDCCs in the rat basilar artery. 2. The relative expression of VDCC subtypes was assessed using quantitative polymerase chain reaction and immunohistochemistry. Data were correlated with physiological studies of vascular function. Domains I-II of the T channel subtypes expressed in the rat basilar artery were cloned and sequenced. 3. Blockade of L-type channels with nifedipine had no effect on vascular tone. In contrast, in the presence of nifedipine, hyperpolarization of short arterial segments produced relaxation, whereas depolarization of quiescent segments evoked constriction. 4. The mRNA and protein for L- and T-type VDCCs were strongly expressed in the main basilar artery and side branches, with Ca(V)3.1 and Ca(V)1.2 the predominant subtypes. 5. T-Type VDCC blockers (i.e. 1 micromol/L mibefradil, 10 micromol/L pimozide and 100 micromol/L flunarizine) decreased intracellular calcium in smooth muscle cells, relaxed and hyperpolarized arteries, whereas nickel chloride (100 micromol/L) had no effect. In contrast with nifedipine, 10 micromol/L nimodipine produced hyperpolarization and relaxation. 6. When arteries were relaxed with 10 micromol/L U73122 (a phospholipase C inhibitor) in the presence of nifedipine, 40 mmol/L KCl evoked depolarization and constriction, which was significantly reduced by 1 micromol/L mibefradil. 7. Sequencing of domains I-II revealed splice variants of Ca(V)3.1, which may impact on channel activity. 8. We conclude that vascular tone of the rat basilar artery results from calcium influx through nifedipine-insensitive VDCCs with pharmacology consistent with Ca(V)3.1 T-type channels.
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Affiliation(s)
- Manuel F Navarro-Gonzalez
- Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory, Australia
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41
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Baumgart JP, Vitko I, Bidaud I, Kondratskyi A, Lory P, Perez-Reyes E. I-II loop structural determinants in the gating and surface expression of low voltage-activated calcium channels. PLoS One 2008; 3:e2976. [PMID: 18714336 PMCID: PMC2495038 DOI: 10.1371/journal.pone.0002976] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2008] [Accepted: 07/26/2008] [Indexed: 11/25/2022] Open
Abstract
The intracellular loops that interlink the four transmembrane domains of Ca2+- and Na+-channels (Cav, Nav) have critical roles in numerous forms of channel regulation. In particular, the intracellular loop that joins repeats I and II (I–II loop) in high voltage-activated (HVA) Ca2+ channels possesses the binding site for Cavβ subunits and plays significant roles in channel function, including trafficking the α1 subunits of HVA channels to the plasma membrane and channel gating. Although there is considerable divergence in the primary sequence of the I–II loop of Cav1/Cav2 HVA channels and Cav3 LVA/T-type channels, evidence for a regulatory role of the I–II loop in T-channel function has recently emerged for Cav3.2 channels. In order to provide a comprehensive view of the role this intracellular region may play in the gating and surface expression in Cav3 channels, we have performed a structure-function analysis of the I–II loop in Cav3.1 and Cav3.3 channels using selective deletion mutants. Here we show the first 60 amino acids of the loop (post IS6) are involved in Cav3.1 and Cav3.3 channel gating and kinetics, which establishes a conserved property of this locus for all Cav3 channels. In contrast to findings in Cav3.2, deletion of the central region of the I–II loop in Cav3.1 and Cav3.3 yielded a modest increase (+30%) and a reduction (−30%) in current density and surface expression, respectively. These experiments enrich our understanding of the structural determinants involved in Cav3 function by highlighting the unique role played by the intracellular I–II loop in Cav3.2 channel trafficking, and illustrating the prominent role of the gating brake in setting the slow and distinctive slow activation kinetics of Cav3.3.
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Affiliation(s)
- Joel P Baumgart
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia, United States of America
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Arias-Olguín II, Vitko I, Fortuna M, Baumgart JP, Sokolova S, Shumilin IA, Van Deusen A, Soriano-García M, Gomora JC, Perez-Reyes E. Characterization of the gating brake in the I-II loop of Ca(v)3.2 T-type Ca(2+) channels. J Biol Chem 2008; 283:8136-44. [PMID: 18218623 DOI: 10.1074/jbc.m708761200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mutations in the I-II loop of Ca(v)3.2 channels were discovered in patients with childhood absence epilepsy. All of these mutations increased the surface expression of the channel, whereas some mutations, and in particular C456S, altered the biophysical properties of channels. Deletions around C456S were found to produce channels that opened at even more negative potentials than control, suggesting the presence of a gating brake that normally prevents channel opening. The goal of the present study was to identify the minimal sequence of this brake and to provide insights into its structure. A peptide fragment of the I-II loop was purified from bacteria, and its structure was analyzed by circular dichroism. These results indicated that the peptide had a high alpha-helical content, as predicted from secondary structure algorithms. Based on homology modeling, we hypothesized that the proximal region of the I-II loop may form a helix-loop-helix structure. This model was tested by mutagenesis followed by electrophysiological measurement of channel gating. Mutations that disrupted the helices, or the loop region, had profound effects on channel gating, shifting both steady state activation and inactivation curves, as well as accelerating channel kinetics. Mutations designed to preserve the helical structure had more modest effects. Taken together, these studies showed that any mutations in the brake, including C456S, disrupted the structural integrity of the brake and its function to maintain these low voltage-activated channels closed at resting membrane potentials.
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Vitko I, Bidaud I, Arias JM, Mezghrani A, Lory P, Perez-Reyes E. The I-II loop controls plasma membrane expression and gating of Ca(v)3.2 T-type Ca2+ channels: a paradigm for childhood absence epilepsy mutations. J Neurosci 2007; 27:322-30. [PMID: 17215393 PMCID: PMC6672065 DOI: 10.1523/jneurosci.1817-06.2007] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Calcium currents via low-voltage-activated T-type channels mediate burst firing, particularly in thalamic neurons. Considerable evidence supports the hypothesis that overactive T-channels may contribute to thalamocortical dysrhythmia, including absence epilepsy. Single nucleotide polymorphisms in one of the T-channel genes (CACNA1H, which encodes Ca(v)3.2) are associated with childhood absence epilepsy in a Chinese population. Because only a fraction of these polymorphisms are predicted to increase channel activity and neuronal firing, we hypothesized that other channel properties may be affected. Here we describe that all the polymorphisms clustered in the intracellular loop connecting repeats I and II (I-II loop) increase the surface expression of extracellularly tagged Ca(v)3.2 channels. The functional domains within the I-II loop were then mapped by deletion analysis. The first 62 amino acids of the loop (post IS6) are involved in regulating the voltage dependence of channel gating and inactivation. Similarly, the last 15 amino acids of the loop (pre IIS1) are involved in channel inactivation. In contrast, the central region of I-II loop regulates surface expression, with no significant effect on channel biophysics. Electrophysiology, luminometry, fluorescence-activated cell sorting measurements, and confocal microscopy studies demonstrate that deletion of this central region leads to enhanced surface expression of channels from intracellular compartments to the plasma membrane. These results provide novel insights into how CACNA1H polymorphisms may contribute to Ca(v)3.2 channel overactivity and consequently to absence epilepsy and establish the I-II loop as an important regulator of Ca(v)3.2 channel function and expression.
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Affiliation(s)
- Iuliia Vitko
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22904, and
| | - Isabelle Bidaud
- Departement de Physiologie, Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5203, Institut National de la Santé et de la Recherche Médicale, Unité 661, Université Montpellier I et II, 34090 Montpellier, France
| | - Juan Manuel Arias
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22904, and
| | - Alexandre Mezghrani
- Departement de Physiologie, Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5203, Institut National de la Santé et de la Recherche Médicale, Unité 661, Université Montpellier I et II, 34090 Montpellier, France
| | - Philippe Lory
- Departement de Physiologie, Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5203, Institut National de la Santé et de la Recherche Médicale, Unité 661, Université Montpellier I et II, 34090 Montpellier, France
| | - Edward Perez-Reyes
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22904, and
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Yang SN, Berggren PO. The role of voltage-gated calcium channels in pancreatic beta-cell physiology and pathophysiology. Endocr Rev 2006; 27:621-76. [PMID: 16868246 DOI: 10.1210/er.2005-0888] [Citation(s) in RCA: 175] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Voltage-gated calcium (CaV) channels are ubiquitously expressed in various cell types throughout the body. In principle, the molecular identity, biophysical profile, and pharmacological property of CaV channels are independent of the cell type where they reside, whereas these channels execute unique functions in different cell types, such as muscle contraction, neurotransmitter release, and hormone secretion. At least six CaValpha1 subunits, including CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1, have been identified in pancreatic beta-cells. These pore-forming subunits complex with certain auxiliary subunits to conduct L-, P/Q-, N-, R-, and T-type CaV currents, respectively. beta-Cell CaV channels take center stage in insulin secretion and play an important role in beta-cell physiology and pathophysiology. CaV3 channels become expressed in diabetes-prone mouse beta-cells. Point mutation in the human CaV1.2 gene results in excessive insulin secretion. Trinucleotide expansion in the human CaV1.3 and CaV2.1 gene is revealed in a subgroup of patients with type 2 diabetes. beta-Cell CaV channels are regulated by a wide range of mechanisms, either shared by other cell types or specific to beta-cells, to always guarantee a satisfactory concentration of Ca2+. Inappropriate regulation of beta-cell CaV channels causes beta-cell dysfunction and even death manifested in both type 1 and type 2 diabetes. This review summarizes current knowledge of CaV channels in beta-cell physiology and pathophysiology.
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Affiliation(s)
- Shao-Nian Yang
- The Rolf Luft Research Center for Diabetes and Endocrinology L1:03, Karolinska University Hospital Solna, SE-171 76 Stockholm, Sweden.
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Hamid J, Peloquin JB, Monteil A, Zamponi GW. Determinants of the differential gating properties of Cav3.1 and Cav3.3 T-type channels: a role of domain IV? Neuroscience 2006; 143:717-28. [PMID: 16996222 DOI: 10.1016/j.neuroscience.2006.08.023] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Revised: 08/11/2006] [Accepted: 08/15/2006] [Indexed: 11/24/2022]
Abstract
We have investigated the channel structural determinants that underlie the difference in gating properties of Cav3.1 and Cav3.3 T-type channels, by creating a series of chimeric channel constructs in which the major transmembrane domains were swapped. The chimeras were then expressed in tsA-201 cells and subjected to whole cell patch clamp analysis. Our data reveal that domains I and IV are major determinants of the half-activation potential. Substitution of domain IV was the most important determinant of activation time constant and time constant for recovery from inactivation, with domains I and II mediating a smaller role. In contrast, the carboxy terminal region did not appear to be involved. Determinants of the time constant for inactivation could not be localized to a specific transmembrane domain, but the concomitant substitution of domains I+IV was able to partially confer the inactivation kinetics among the two wild type channels. Our data indicate that the domain IV region mediates an important role in T-type channel activation, whereas multiple channel structural determinants appear to control T-type channel inactivation.
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Affiliation(s)
- J Hamid
- Hotchkiss Brain Institute and Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Drive Northwest, Calgary, Canada T2N 4N1
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