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El Ghaleb Y, Ortner NJ, Posch W, Fernández-Quintero ML, Tuinte WE, Monteleone S, Draheim HJ, Liedl KR, Wilflingseder D, Striessnig J, Tuluc P, Flucher BE, Campiglio M. Calcium current modulation by the γ1 subunit depends on alternative splicing of CaV1.1. J Gen Physiol 2022; 154:e202113028. [PMID: 35349630 PMCID: PMC9037348 DOI: 10.1085/jgp.202113028] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Accepted: 03/08/2022] [Indexed: 01/01/2023] Open
Abstract
The skeletal muscle voltage-gated calcium channel (CaV1.1) primarily functions as a voltage sensor for excitation-contraction coupling. Conversely, its ion-conducting function is modulated by multiple mechanisms within the pore-forming α1S subunit and the auxiliary α2δ-1 and γ1 subunits. In particular, developmentally regulated alternative splicing of exon 29, which inserts 19 amino acids in the extracellular IVS3-S4 loop of CaV1.1a, greatly reduces the current density and shifts the voltage dependence of activation to positive potentials outside the physiological range. We generated new HEK293 cell lines stably expressing α2δ-1, β3, and STAC3. When the adult (CaV1.1a) and embryonic (CaV1.1e) splice variants were expressed in these cells, the difference in the voltage dependence of activation observed in muscle cells was reproduced, but not the reduced current density of CaV1.1a. Only when we further coexpressed the γ1 subunit was the current density of CaV1.1a, but not that of CaV1.1e, reduced by >50%. In addition, γ1 caused a shift of the voltage dependence of inactivation to negative voltages in both variants. Thus, the current-reducing effect of γ1, unlike its effect on inactivation, is specifically dependent on the inclusion of exon 29 in CaV1.1a. Molecular structure modeling revealed several direct ionic interactions between residues in the IVS3-S4 loop and the γ1 subunit. However, substitution of these residues by alanine, individually or in combination, did not abolish the γ1-dependent reduction of current density, suggesting that structural rearrangements in CaV1.1a induced by inclusion of exon 29 may allosterically empower the γ1 subunit to exert its inhibitory action on CaV1.1 calcium currents.
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Affiliation(s)
- Yousra El Ghaleb
- Institute of Physiology, Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria
| | - Nadine J. Ortner
- Department of Pharmacology and Toxicology, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria
| | - Wilfried Posch
- Institute of Hygiene and Medical Microbiology, Medical University of Innsbruck, Innsbruck, Austria
| | | | - Wietske E. Tuinte
- Institute of Physiology, Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria
| | - Stefania Monteleone
- Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innsbruck, Austria
| | - Henning J. Draheim
- Boehringer Ingelheim Pharma GmbH & Co KG, CNS Research, Biberach an der Riss, Germany
| | - Klaus R. Liedl
- Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innsbruck, Austria
| | - Doris Wilflingseder
- Institute of Hygiene and Medical Microbiology, Medical University of Innsbruck, Innsbruck, Austria
| | - Jörg Striessnig
- Department of Pharmacology and Toxicology, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria
| | - Petronel Tuluc
- Department of Pharmacology and Toxicology, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria
| | - Bernhard E. Flucher
- Institute of Physiology, Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria
| | - Marta Campiglio
- Institute of Physiology, Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria
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2
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Melzer W. From α1s splicing to γ1 function: A new twist in subunit modulation of the skeletal muscle L-type Ca2+ channel. J Gen Physiol 2022; 154:213270. [PMID: 35674662 PMCID: PMC9184848 DOI: 10.1085/jgp.202213182] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Melzer discusses a recent JGP study showing that alternative splicing of the skeletal muscle L-type calcium channel impacts on a modulatory effect of its γ subunit.
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Affiliation(s)
- Werner Melzer
- Institute of Applied Physiology, Ulm University, Ulm, Germany
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Miranda DR, Voss AA, Bannister RA. Into the spotlight: RGK proteins in skeletal muscle. Cell Calcium 2021; 98:102439. [PMID: 34261001 DOI: 10.1016/j.ceca.2021.102439] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 06/24/2021] [Accepted: 06/26/2021] [Indexed: 10/20/2022]
Abstract
The RGK (Rad, Rem, Rem2 and Gem/Kir) family of small GTPases are potent endogenous inhibitors of voltage-gated Ca2+ channels (VGCCs). While the impact of RGK proteins on cardiac physiology has been investigated extensively, much less is known regarding their influence on skeletal muscle biology. Thus, the purpose of this article is to establish a basis for future investigation into the role of RGK proteins in regulating the skeletal muscle excitation-contraction (EC) coupling complex via modulation of the L-type CaV1.1 VGCC. The pathological consequences of elevated muscle RGK protein expression in Type II Diabetes, Amyotrophic Lateral Sclerosis (ALS), Duchenne's Muscular Dystrophy and traumatic nerve injury are also discussed.
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Affiliation(s)
- Daniel R Miranda
- Department of Biological Sciences, College of Science and Mathematics, Wright State University, 235A Biological Sciences, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA
| | - Andrew A Voss
- Department of Biological Sciences, College of Science and Mathematics, Wright State University, 235A Biological Sciences, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA.
| | - Roger A Bannister
- Departments of Pathology and Biochemistry & Molecular Biology, University of Maryland School of Medicine, 108 North Greene Street, Baltimore, MD 21201, USA.
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Stac3 has a direct role in skeletal muscle-type excitation-contraction coupling that is disrupted by a myopathy-causing mutation. Proc Natl Acad Sci U S A 2016; 113:10986-91. [PMID: 27621462 DOI: 10.1073/pnas.1612441113] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In skeletal muscle, conformational coupling between CaV1.1 in the plasma membrane and type 1 ryanodine receptor (RyR1) in the sarcoplasmic reticulum (SR) is thought to underlie both excitation-contraction (EC) coupling Ca(2+) release from the SR and retrograde coupling by which RyR1 increases the magnitude of the Ca(2+) current via CaV1.1. Recent work has shown that EC coupling fails in muscle from mice and fish null for the protein Stac3 (SH3 and cysteine-rich domain 3) but did not establish the functional role of Stac3 in the CaV1.1-RyR1 interaction. We investigated this using both tsA201 cells and Stac3 KO myotubes. While confirming in tsA201 cells that Stac3 could support surface expression of CaV1.1 (coexpressed with its auxiliary β1a and α2-δ1 subunits) and the generation of large Ca(2+) currents, we found that without Stac3 the auxiliary γ1 subunit also supported membrane expression of CaV1.1/β1a/α2-δ1, but that this combination generated only tiny Ca(2+) currents. In Stac3 KO myotubes, there was reduced, but still substantial CaV1.1 in the plasma membrane. However, the CaV1.1 remaining in Stac3 KO myotubes did not generate appreciable Ca(2+) currents or EC coupling Ca(2+) release. Expression of WT Stac3 in Stac3 KO myotubes fully restored Ca(2+) currents and EC coupling Ca(2+) release, whereas expression of Stac3W280S (containing the Native American myopathy mutation) partially restored Ca(2+) currents but only marginally restored EC coupling. We conclude that membrane trafficking of CaV1.1 is facilitated by, but does not require, Stac3, and that Stac3 is directly involved in conformational coupling between CaV1.1 and RyR1.
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Ohrtman JD, Romberg CF, Moua O, Bannister RA, Levinson SR, Beam KG. Apparent lack of physical or functional interaction between CaV1.1 and its distal C terminus. ACTA ACUST UNITED AC 2015; 145:303-14. [PMID: 25779869 PMCID: PMC4380213 DOI: 10.1085/jgp.201411292] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The distal C-terminal domain of CaV1.1 is not required for depolarization-induced potentiation of L-type Ca2+ current in skeletal muscle. CaV1.1 acts as both the voltage sensor that triggers excitation–contraction coupling in skeletal muscle and as an L-type Ca2+ channel. It has been proposed that, after its posttranslational cleavage, the distal C terminus of CaV1.1 remains noncovalently associated with proximal CaV1.1, and that tethering of protein kinase A to the distal C terminus is required for depolarization-induced potentiation of L-type Ca2+ current in skeletal muscle. Here, we report that association of the distal C terminus with proximal CaV1.1 cannot be detected by either immunoprecipitation of mouse skeletal muscle or by colocalized fluorescence after expression in adult skeletal muscle fibers of a CaV1.1 construct labeled with yellow fluorescent protein (YFP) and cyan fluorescent protein on the N and C termini, respectively. We found that L-type Ca2+ channel activity was similar after expression of constructs that either did (YFP-CaV1.11860) or did not (YFP-CaV1.11666) contain coding sequence for the distal C-terminal domain in dysgenic myotubes null for endogenous CaV1.1. Furthermore, in response to strong (up to 90 mV) or long-lasting prepulses (up to 200 ms), tail current amplitudes and decay times were equally increased in dysgenic myotubes expressing either YFP-CaV1.11860 or YFP-CaV1.11666, suggesting that the distal C-terminal domain was not required for depolarization-induced potentiation. Thus, our experiments do not support the existence of either biochemical or functional interactions between proximal CaV1.1 and the distal C terminus.
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Affiliation(s)
- Joshua D Ohrtman
- Department of Physiology and Biophysics and Department of Medicine-Cardiology Division, University of Colorado, Denver, Aurora, CO 80045
| | - Christin F Romberg
- Department of Physiology and Biophysics and Department of Medicine-Cardiology Division, University of Colorado, Denver, Aurora, CO 80045
| | - Ong Moua
- Department of Physiology and Biophysics and Department of Medicine-Cardiology Division, University of Colorado, Denver, Aurora, CO 80045
| | - Roger A Bannister
- Department of Physiology and Biophysics and Department of Medicine-Cardiology Division, University of Colorado, Denver, Aurora, CO 80045
| | - S Rock Levinson
- Department of Physiology and Biophysics and Department of Medicine-Cardiology Division, University of Colorado, Denver, Aurora, CO 80045
| | - Kurt G Beam
- Department of Physiology and Biophysics and Department of Medicine-Cardiology Division, University of Colorado, Denver, Aurora, CO 80045
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Antanavičiūtė I, Ereminienė E, Vysockas V, Račkauskas M, Skipskis V, Rysevaitė K, Treinys R, Benetis R, Jurevičius J, Skeberdis VA. Exogenous connexin43-expressing autologous skeletal myoblasts ameliorate mechanical function and electrical activity of the rabbit heart after experimental infarction. Int J Exp Pathol 2014; 96:42-53. [PMID: 25529770 DOI: 10.1111/iep.12109] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 10/26/2014] [Indexed: 12/19/2022] Open
Abstract
Acute myocardial infarction is one of the major causes of mortality worldwide. For regeneration of the rabbit heart after experimentally induced infarction we used autologous skeletal myoblasts (SMs) due to their high proliferative potential, resistance to ischaemia and absence of immunological and ethical concerns. The cells were characterized with muscle-specific and myogenic markers. Cell transplantation was performed by injection of cell suspension (0.5 ml) containing approximately 6 million myoblasts into the infarction zone. The animals were divided into four groups: (i) no injection; (ii) sham injected; (iii) injected with wild-type SMs; and (iv) injected with SMs expressing connexin43 fused with green fluorescent protein (Cx43EGFP). Left ventricular ejection fraction (LVEF) was evaluated by 2D echocardiography in vivo before infarction, when myocardium has stabilized after infarction, and 3 months after infarction. Electrical activity in the healthy and infarction zones of the heart was examined ex vivo in Langendorff-perfused hearts by optical mapping using di-4-ANEPPS, a potential sensitive fluorescent dye. We demonstrate that SMs in the coculture can couple electrically not only to abutted but also to remote acutely isolated allogenic cardiac myocytes through membranous tunnelling tubes. The beneficial effect of cellular therapy on LVEF and electrical activity was observed in the group of animals injected with Cx43EGFP-expressing SMs. L-type Ca(2+) current amplitude was approximately fivefold smaller in the isolated SMs compared to healthy myocytes suggesting that limited recovery of LVEF may be related to inadequate expression or function of L-type Ca(2+) channels in transplanted differentiating SMs.
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Affiliation(s)
- Ieva Antanavičiūtė
- Institute of Cardiology, Medical Academy, Lithuanian University of Health Sciences, Kaunas, Lithuania
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Bannister RA, Beam KG. Ca(V)1.1: The atypical prototypical voltage-gated Ca²⁺ channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:1587-97. [PMID: 22982493 DOI: 10.1016/j.bbamem.2012.09.007] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2012] [Revised: 09/04/2012] [Accepted: 09/05/2012] [Indexed: 11/28/2022]
Abstract
Ca(V)1.1 is the prototype for the other nine known Ca(V) channel isoforms, yet it has functional properties that make it truly atypical of this group. Specifically, Ca(V)1.1 is expressed solely in skeletal muscle where it serves multiple purposes; it is the voltage sensor for excitation-contraction coupling and it is an L-type Ca²⁺ channel which contributes to a form of activity-dependent Ca²⁺ entry that has been termed Excitation-coupled Ca²⁺ entry. The ability of Ca(V)1.1 to serve as voltage-sensor for excitation-contraction coupling appears to be unique among Ca(V) channels, whereas the physiological role of its more conventional function as a Ca²⁺ channel has been a matter of uncertainty for nearly 50 years. In this chapter, we discuss how Ca(V)1.1 supports excitation-contraction coupling, the possible relevance of Ca²⁺ entry through Ca(V)1.1 and how alterations of Ca(V)1.1 function can have pathophysiological consequences. This article is part of a Special Issue entitled: Calcium channels.
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Affiliation(s)
- Roger A Bannister
- Department of Medicine, Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO 80045, USA.
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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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Chen RS, Best PM. A Small Peptide Inhibitor of the Low Voltage-Activated Calcium Channel Cav3.1. Mol Pharmacol 2009; 75:1042-51. [DOI: 10.1124/mol.108.052654] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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10
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Lin Z, Witschas K, Garcia T, Chen RS, Hansen JP, Sellers ZM, Kuzmenkina E, Herzig S, Best PM. A critical GxxxA motif in the gamma6 calcium channel subunit mediates its inhibitory effect on Cav3.1 calcium current. J Physiol 2008; 586:5349-66. [PMID: 18818244 DOI: 10.1113/jphysiol.2008.159111] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The eight members of the calcium channel gamma subunit family are integral membrane proteins that regulate the expression and behaviour of voltage and ligand gated ion channels. While a subgroup consisting of gamma(2), gamma(3), gamma(4) and gamma(8) (the TARPs) modulate AMPA receptor localization and function, the gamma(1) and gamma(6) subunits conform to the original description of these proteins as regulators of voltage gated calcium channels. We have previously shown that the gamma(6) subunit is highly expressed in atrial myocytes and that it is capable of acting as a negative modulator of low voltage activated calcium current. In this study we extend our understanding of gamma(6) subunit modulation of low voltage activated calcium current. Using engineered chimeric constructs, we demonstrate that the first transmembrane domain (TM1) of gamma(6) is necessary for its inhibitory effect on Cav3.1 current. Mutational analysis is then used to identify a unique GxxxA motif within TM1 that is required for the function of the subunit strongly suggesting the involvement of helix-helix interactions in its effects. Results from co-immunoprecipitation experiments confirm a physical association of gamma(6) with the Cav3.1 channel in both HEK cells and atrial myocytes. Single channel analysis reveals that binding of gamma(6) reduces channel availability for activation. Taken together, the results of this study provide both a molecular and a mechanistic framework for understanding the unique ability of the gamma(6) calcium channel subunit to modulate low voltage activated (Cav3.1) calcium current density.
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Affiliation(s)
- Zuojun Lin
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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11
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Mutations in a Drosophila alpha2delta voltage-gated calcium channel subunit reveal a crucial synaptic function. J Neurosci 2008; 28:31-8. [PMID: 18171920 DOI: 10.1523/jneurosci.4498-07.2008] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Voltage-dependent calcium channels regulate many aspects of neuronal biology, including synaptic transmission. In addition to their alpha1 subunit, which encodes the essential voltage gate and selective pore, calcium channels also contain auxiliary alpha2delta, beta, and gamma subunits. Despite progress in understanding the biophysical properties of calcium channels, the in vivo functions of these auxiliary subunits remain unclear. We have isolated mutations in the gene encoding an alpha2delta calcium channel subunit (d alpha2delta-3) using a forward genetic screen in Drosophila. Null mutations in this gene are embryonic lethal and can be rescued by expression in the nervous system, demonstrating that the essential function of this subunit is neuronal. The photoreceptor phenotype of d alpha2delta-3 mutants resembles that of the calcium channel alpha1 mutant cacophony (cac), suggesting shared functions. We have examined in detail genotypes that survive to the third-instar stage. Electrophysiological recordings demonstrate that synaptic transmission is severely impaired in these mutants. Thus the alpha2delta calcium channel subunit is critical for calcium-dependent synaptic function. As such, this Drosophila isoform is the likely partner to the presynaptic calcium channel alpha1 subunit encoded by the cac locus. Consistent with this hypothesis, cacGFP fluorescence at the neuromuscular junction is reduced in d alpha2delta-3 mutants. This is the first characterization of an alpha2delta-3 mutant in any organism and indicates a necessary role for alpha2delta-3 in presynaptic vesicle release and calcium channel expression at active zones.
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Nguemo F, Fleischmann BK, Schunkert H, Hescheler J, Reppel M. Functional Expression and Inactivation of L-type Ca 2+ Currents During Murine Heart Development -Implications for Cardiac Ca 2+ Homeostasis. Cell Physiol Biochem 2007; 20:809-24. [DOI: 10.1159/000110441] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/09/2007] [Indexed: 11/19/2022] Open
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Sandoval A, Arikkath J, Monjaraz E, Campbell KP, Felix R. gamma1-dependent down-regulation of recombinant voltage-gated Ca2+ channels. Cell Mol Neurobiol 2007; 27:901-8. [PMID: 17934806 DOI: 10.1007/s10571-007-9210-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2007] [Accepted: 08/28/2007] [Indexed: 10/22/2022]
Abstract
(1) Voltage-gated Ca2+ (CaV) channels are multi-subunit membrane complexes that allow depolarization-induced Ca2+ influx into cells. The skeletal muscle L-type CaV channels consist of an ion-conducting CaV1.1 subunit and auxiliary alpha2delta-1, beta1 and gamma1 subunits. This complex serves both as a CaV channel and as a voltage sensor for excitation-contraction coupling. (2) Though much is known about the mechanisms by which the alpha2delta-1 and beta1 subunits regulate CaV channel function, there is far less information on the gamma1 subunit. Previously, we characterized the interaction of gamma1 with the other components of the skeletal CaV channel complex, and showed that heterologous expression of this auxiliary subunit decreases Ca2+ current density in myotubes from gamma1 null mice. (3) In the current report, using Western blotting we show that the expression of the CaV1.1 protein is significantly lower when it is heterologously co-expressed with gamma1. Consistent with this, patch-clamp recordings showed that transient transfection of gamma1 drastically inhibited macroscopic currents through recombinant N-type (CaV2.2/alpha2delta-1/beta3) channels expressed in HEK-293 cells. (4) These findings provide evidence that co-expression of the auxiliary gamma1 subunit results in a decreased expression of the ion-conducting subunit, which may help to explain the reduction in Ca2+ current density following gamma1 transfection.
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Affiliation(s)
- Alejandro Sandoval
- .Department of Cell Biology, Center for Research and Advanced Studies of the National Polytechnic Institute Cinvestav-IPN, Avenida IPN 2508, Colonia Zacatenco, Mexico City, DF CP 07300, Mexico
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Gross SA, Wissenbach U, Philipp SE, Freichel M, Cavalié A, Flockerzi V. Murine ORAI2 splice variants form functional Ca2+ release-activated Ca2+ (CRAC) channels. J Biol Chem 2007; 282:19375-84. [PMID: 17463004 DOI: 10.1074/jbc.m701962200] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The stimulation of membrane receptors coupled to the phopholipase C pathway leads to activation of the Ca(2+) release-activated Ca(2+) (CRAC) channels. Recent evidence indicates that ORAI1 is an essential pore subunit of CRAC channels. STIM1 is additionally required for CRAC channel activation. The present study focuses on the genomic organization, tissue expression pattern, and functional properties of the murine ORAI2. Additionally, we report the cloning of the murine ORAI1, ORAI3, and STIM1. Two chromosomal loci were identified for the murine orai2 gene, one containing an intronless gene and a second locus that gives rise to the splice variants ORAI2 long (ORAI2L) and ORAI2 short (ORAI2S). Northern blots revealed a prominent expression of the ORAI2 variants in the brain, lung, spleen, and intestine, while ORAI1, ORAI3, and STIM1 appeared to be near ubiquitously expressed in mice tissues. Specific antibodies detected ORAI2 in RBL 2H3 but not in HEK 293 cells, whereas both cell lines appeared to express ORAI1 and STIM1 proteins. Co-expression experiments with STIM1 and either ORAI1 or ORAI2 variants showed that ORAI2L and ORAI2S enhanced substantially CRAC current densities in HEK 293 but were ineffective in RBL 2H3 cells, whereas ORAI1 strongly amplified CRAC currents in both cell lines. Thus, the capability of ORAI2 variants to form CRAC channels depends strongly on the cell background. Additionally, CRAC channels formed by ORAI2S were strongly sensitive to inactivation by internal Ca(2+). When co-expressed with STIM1 and ORAI1, ORAI2S apparently plays a negative dominant role in the formation of CRAC channels.
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Affiliation(s)
- Stefan Alfred Gross
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg/Saar, Germany
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Chen RS, Deng TC, Garcia T, Sellers ZM, Best PM. Calcium channel γ subunits: a functionally diverse protein family. Cell Biochem Biophys 2007; 47:178-86. [PMID: 17652770 DOI: 10.1007/s12013-007-0002-0] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/1999] [Revised: 11/30/1999] [Accepted: 11/30/1999] [Indexed: 10/23/2022]
Abstract
The calcium channel gamma subunits comprise an eight-member protein family that share a common topology consisting of four transmembrane domains and intracellular N- and C-termini. Although the first gamma subunit was identified as an auxiliary subunit of a voltage-dependent calcium channel, a review of phylogenetic, bioinformatic, and functional studies indicates that they are a functionally diverse protein family. A cluster containing gamma1 and gamma6 conforms to the original description of the protein family as they seem to act primarily as subunits of calcium channels expressed in muscle. Members of a second cluster (gamma2, gamma3, gamma4, gamma8) function as regulators of AMPA receptor localization and function in the brain and are collectively known as TARPs. The function of members of the third cluster (gamma5, gamma7) remains unclear. Our analysis shows that the members of each cluster contain conserved regulatory motifs that help to differentiate the groups. However, the physiological significance of these motifs in many cases remains to be demonstrated.
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Affiliation(s)
- Ren-Shiang Chen
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, 524 Burrill Hall, 407 S Goodwin Avenue, Urbana, IL 61801, USA
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16
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Melzer W, Andronache Z, Ursu D. Functional roles of the gamma subunit of the skeletal muscle DHP-receptor. J Muscle Res Cell Motil 2006; 27:307-14. [PMID: 16897572 DOI: 10.1007/s10974-006-9093-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2006] [Accepted: 07/12/2006] [Indexed: 10/24/2022]
Abstract
In excitation-contraction coupling (EC coupling) of skeletal muscle, large and rapid changes of the myoplasmic Ca2+ concentration mediate the activation and termination of force. The L-type Ca2+ channel (dihydropyridine receptor, DHP receptor) is a central component of the EC coupling process. Its predominant role is to provide the Ca2+ release channels of the sarcoplasmic reticulum (SR) with the sensitivity to cell membrane voltage. The DHP receptor consists of five different proteins (alpha1S, beta1, gamma1, delta and alpha2) whose tasks and functional characteristics are still incompletely understood. This short review summarizes progress made in studying the physiology of the gamma1 subunit, a membrane polypeptide that is highly specific for skeletal muscle. The focus is on recent results obtained from muscle of gamma1-deficient mice.
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Affiliation(s)
- Werner Melzer
- Department of Applied Physiology, University of Ulm, Albert-Einstein-Allee 11, D-89069, Ulm, Germany.
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Fukaya M, Yamazaki M, Sakimura K, Watanabe M. Spatial diversity in gene expression for VDCCγ subunit family in developing and adult mouse brains. Neurosci Res 2005; 53:376-83. [PMID: 16171881 DOI: 10.1016/j.neures.2005.08.009] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2005] [Revised: 08/22/2005] [Accepted: 08/22/2005] [Indexed: 11/24/2022]
Abstract
The gamma subunit of voltage-dependent Ca2+ channels (VDCCs) is characterized by molecular diversity and regulation of AMPA-type glutamate receptors as well as VDCCs. In the present study, we examined expressions for the VDCCgamma1-8 subunit mRNAs in developing and adult mouse brains by in situ hybridization. In adult brains, the gamma2 and gamma7 subunit mRNAs were widely expressed in various grey matter regions with the highest level in cerebellar Purkinje cells and granule cells. The gamma3 and gamma8 subunit mRNAs predominated in the telencephalon, with the latter being at striking levels in the hippocampus. The gamma4 subunit mRNA was enriched in the olfactory bulb, striatum, thalamus and hypothalamus. The gamma5 subunit mRNA was abundant in the olfactory bulb, hippocampal CA2, thalamus, inferior colliculus and Bergmann glia. Transcripts of these subunits were detected in embryonic brains: some showed well-preserved spatial patterns (gamma2, gamma5, gamma7 and gamma8), while others underwent developmental up- (gamma3) or down-regulation (gamma4). In contrast, the gamma1 and gamma6 subunit mRNAs were negative or very low throughout brain development. Therefore, the present study has revealed spatial diversity in gene expression for individual VDCCgamma subunits, presumably reflecting functional diversity of this protein family and their differential involvement in neural function.
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Affiliation(s)
- Masahiro Fukaya
- Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo 060-8638, Japan.
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Ursu D, Schuhmeier RP, Freichel M, Flockerzi V, Melzer W. Altered inactivation of Ca2+ current and Ca2+ release in mouse muscle fibers deficient in the DHP receptor gamma1 subunit. ACTA ACUST UNITED AC 2005; 124:605-18. [PMID: 15504904 PMCID: PMC2234002 DOI: 10.1085/jgp.200409168] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Functional impacts of the skeletal muscle-specific Ca2+ channel subunit gamma1 have previously been studied using coexpression with the cardiac alpha1C polypeptide in nonmuscle cells and primary-cultured myotubes of gamma1-deficient mice. Data from single adult muscle fibers of gamma-/- mice are not yet available. In the present study, we performed voltage clamp experiments on enzymatically isolated mature muscle fibers of the m. interosseus obtained from gamma+/+ and gamma-/- mice. We measured L-type Ca2+ inward currents and intracellular Ca2+ transients during 100-ms step depolarizations from a holding potential of -80 mV. Ratiometric Ca2+ transients were analyzed with a removal model fit approach to calculate the flux of Ca2+ from the sarcoplasmic reticulum. Ca2+ current density, Ca2+ release flux, and the voltage dependence of activation of both Ca2+ current and Ca2+ release were not significantly different. By varying the holding potential and recording Ca2+ current and Ca2+ release flux induced by 100-ms test depolarizations to +20 mV, we studied quasi-steady-state properties of slow voltage-dependent inactivation. For the Ca2+ current, these experiments showed a right-shifted voltage dependence of inactivation. Importantly, we could demonstrate that a very similar shift occurred also in the inactivation curve of Ca2+ release. Voltages of half maximal inactivation were altered by 16 (current) and 14 mV (release), respectively. Muscle fiber bundles, activated by elevated potassium concentration (120 mM), developed about threefold larger contracture force in gamma-/- compared with gamma+/+. This difference was independent of the presence of extracellular Ca2+ and likely results from the lower sensitivity to voltage-dependent inactivation of Ca2+ release. These results demonstrate a specific alteration of voltage-dependent inactivation of both Ca2+ entry and Ca2+ release by the gamma1 subunit of the dihydropyridine receptor in mature muscle fibers of the mouse.
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Affiliation(s)
- Daniel Ursu
- University of Ulm, Dept. of Applied Physiology, Albert-Einstein-Allee 11, D-89069 Ulm, Germany
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