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Jin JY, Guo BB, Dong Y, Sheng Y, Fan LL, Zhang LB. Case Report: A Novel CACNA1S Mutation Associated With Hypokalemic Periodic Paralysis in a Chinese Family. Front Genet 2021; 12:743184. [PMID: 34777470 PMCID: PMC8586648 DOI: 10.3389/fgene.2021.743184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2021] [Accepted: 10/12/2021] [Indexed: 11/13/2022] Open
Abstract
Hypokalemic periodic paralysis (HypoPP) is a rare autosomal dominant disorder characterized by episodic flaccid paralysis with concomitant hypokalemia. More than half of patients were associated with mutations in CACNA1S that encodes the alpha-1-subunit of the skeletal muscle L-type voltage-dependent calcium channel. Mutations in CACNA1S may alter the structure of CACNA1S and affect the functions of calcium channels, which damages Ca2+-mediated excitation-contraction coupling. In this research, we identified and described a Chinese HypoPP patient with a novel frameshift mutation in CACNA1S [NM_000069.2: c.1364delA (p.Asn455fs)] by targeted sequencing. This study would expand the spectrum of CACNA1S mutations, further our understanding of HypoPP, and provided a new perspective for selecting effective treatments.
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Affiliation(s)
- Jie-Yuan Jin
- School of Life Sciences, Central South University, Changsha, China.,Hunan Key Laboratory of Animal Models for Human Diseases, School of Life Sciences, Central South University, Changsha, China
| | - Bing-Bing Guo
- School of Life Sciences, Central South University, Changsha, China.,Hunan Key Laboratory of Animal Models for Human Diseases, School of Life Sciences, Central South University, Changsha, China.,CAS Key Laboratory of Infection and Immunity, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Yi Dong
- School of Life Sciences, Central South University, Changsha, China
| | - Yue Sheng
- School of Life Sciences, Central South University, Changsha, China
| | - Liang-Liang Fan
- School of Life Sciences, Central South University, Changsha, China.,Hunan Key Laboratory of Animal Models for Human Diseases, School of Life Sciences, Central South University, Changsha, China.,Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, China
| | - Li-Bing Zhang
- Department of Pediatrics, Affiliated Hospital of Yangzhou University, Yangzhou, China
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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: 10] [Impact Index Per Article: 3.3] [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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Bannister RA. Bridging the myoplasmic gap II: more recent advances in skeletal muscle excitation-contraction coupling. ACTA ACUST UNITED AC 2016; 219:175-82. [PMID: 26792328 DOI: 10.1242/jeb.124123] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
In skeletal muscle, excitation-contraction (EC) coupling relies on the transmission of an intermolecular signal from the voltage-sensing regions of the L-type Ca(2+) channel (Ca(V)1.1) in the plasma membrane to the channel pore of the type 1 ryanodine receptor (RyR1) nearly 10 nm away in the membrane of the sarcoplasmic reticulum (SR). Even though the roles of Ca(V)1.1 and RyR1 as voltage sensor and SR Ca(2+) release channel, respectively, have been established for nearly 25 years, the mechanism underlying communication between these two channels remains undefined. In the course of this article, I will review current viewpoints on this topic with particular emphasis on recent studies.
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Affiliation(s)
- Roger A Bannister
- Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, 12700 East 19th Avenue, Room 8006, B-139, Aurora, CO 80045, USA
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4
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Lueck JD, Mackey AL, Infield DT, Galpin JD, Li J, Roux B, Ahern CA. Atomic mutagenesis in ion channels with engineered stoichiometry. eLife 2016; 5. [PMID: 27710770 PMCID: PMC5092047 DOI: 10.7554/elife.18976] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Accepted: 10/05/2016] [Indexed: 12/28/2022] Open
Abstract
C-type inactivation of potassium channels fine-tunes the electrical signaling in excitable cells through an internal timing mechanism that is mediated by a hydrogen bond network in the channels' selectively filter. Previously, we used nonsense suppression to highlight the role of the conserved Trp434-Asp447 indole hydrogen bond in Shaker potassium channels with a non-hydrogen bonding homologue of tryptophan, Ind (Pless et al., 2013). Here, molecular dynamics simulations indicate that the Trp434Ind hydrogen bonding partner, Asp447, unexpectedly 'flips out' towards the extracellular environment, allowing water to penetrate the space behind the selectivity filter while simultaneously reducing the local negative electrostatic charge. Additionally, a protein engineering approach is presented whereby split intein sequences are flanked by endoplasmic reticulum retention/retrieval motifs (ERret) are incorporated into the N- or C- termini of Shaker monomers or within sodium channels two-domain fragments. This system enabled stoichiometric control of Shaker monomers and the encoding of multiple amino acids within a channel tetramer. DOI:http://dx.doi.org/10.7554/eLife.18976.001
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Affiliation(s)
- John D Lueck
- Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, United States
| | - Adam L Mackey
- Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, United States
| | - Daniel T Infield
- Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, United States
| | - Jason D Galpin
- Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, United States
| | - Jing Li
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States
| | - Christopher A Ahern
- Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, United States
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5
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Liao P, Yu D, Hu Z, Liang MC, Wang JJ, Yu CY, Ng G, Yong TF, Soon JL, Chua YL, Soong TW. Alternative splicing generates a novel truncated Cav1.2 channel in neonatal rat heart. J Biol Chem 2015; 290:9262-72. [PMID: 25694430 DOI: 10.1074/jbc.m114.594911] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Indexed: 11/06/2022] Open
Abstract
L-type Cav1.2 Ca(2+) channel undergoes extensive alternative splicing, generating functionally different channels. Alternatively spliced Cav1.2 Ca(2+) channels have been found to be expressed in a tissue-specific manner or under pathological conditions. To provide a more comprehensive understanding of alternative splicing in Cav1.2 channel, we systematically investigated the splicing patterns in the neonatal and adult rat hearts. The neonatal heart expresses a novel 104-bp exon 33L at the IVS3-4 linker that is generated by the use of an alternative acceptor site. Inclusion of exon 33L causes frameshift and C-terminal truncation. Whole-cell electrophysiological recordings of Cav1.233L channels expressed in HEK 293 cells did not detect any current. However, when co-expressed with wild type Cav1.2 channels, Cav1.233L channels reduced the current density and altered the electrophysiological properties of the wild type Cav1.2 channels. Interestingly, the truncated 3.5-domain Cav1.233L channels also yielded a dominant negative effect on Cav1.3 channels, but not on Cav3.2 channels, suggesting that Cavβ subunits is required for Cav1.233L regulation. A biochemical study provided evidence that Cav1.233L channels enhanced protein degradation of wild type channels via the ubiquitin-proteasome system. Although the physiological significance of the Cav1.233L channels in neonatal heart is still unknown, our report demonstrates the ability of this novel truncated channel to modulate the activity of the functional Cav1.2 channels. Moreover, the human Cav1.2 channel also contains exon 33L that is developmentally regulated in heart. Unexpectedly, human exon 33L has a one-nucleotide insertion that allowed in-frame translation of a full Cav1.2 channel. An electrophysiological study showed that human Cav1.233L channel is a functional channel but conducts Ca(2+) ions at a much lower level.
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Affiliation(s)
- Ping Liao
- From the National Neuroscience Institute, 11 Jalan Tan Tock Seng, Singapore 308433, Duke-NUS Graduate Medical School Singapore, Singapore 169857,
| | - Dejie Yu
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, and
| | - Zhenyu Hu
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, and
| | - Mui Cheng Liang
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, and
| | - Jue Jin Wang
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, and
| | - Chye Yun Yu
- From the National Neuroscience Institute, 11 Jalan Tan Tock Seng, Singapore 308433
| | - Gandi Ng
- From the National Neuroscience Institute, 11 Jalan Tan Tock Seng, Singapore 308433
| | - Tan Fong Yong
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, and
| | - Jia Lin Soon
- National Heart Centre Singapore, 5 Hospital Drive, Singapore 169609
| | - Yeow Leng Chua
- National Heart Centre Singapore, 5 Hospital Drive, Singapore 169609
| | - Tuck Wah Soong
- From the National Neuroscience Institute, 11 Jalan Tan Tock Seng, Singapore 308433, Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, and
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Eltit JM, Franzini-Armstrong C, Perez CF. Amino acid residues 489-503 of dihydropyridine receptor (DHPR) β1a subunit are critical for structural communication between the skeletal muscle DHPR complex and type 1 ryanodine receptor. J Biol Chem 2014; 289:36116-24. [PMID: 25384984 DOI: 10.1074/jbc.m114.615526] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The β1a subunit is a cytoplasmic component of the dihydropyridine receptor (DHPR) complex that plays an essential role in skeletal muscle excitation-contraction (EC) coupling. Here we investigate the role of the C-terminal end of this auxiliary subunit in the functional and structural communication between the DHPR and the Ca(2+) release channel (RyR1). Progressive truncation of the β1a C terminus showed that deletion of amino acid residues Gln(489) to Trp(503) resulted in a loss of depolarization-induced Ca(2+) release, a severe reduction of L-type Ca(2+) currents, and a lack of tetrad formation as evaluated by freeze-fracture analysis. However, deletion of this domain did not affect expression/targeting or density (Qmax) of the DHPR-α1S subunit to the plasma membrane. Within this motif, triple alanine substitution of residues Leu(496), Leu(500), and Trp(503), which are thought to mediate direct β1a-RyR1 interactions, weakened EC coupling but did not replicate the truncated phenotype. Therefore, these data demonstrate that an amino acid segment encompassing sequence (489)QVQVLTSLRRNLSFW(503) of β1a contains critical determinant(s) for the physical link of DHPR and RyR1, further confirming a direct correspondence between DHPR positioning and DHPR/RyR functional interactions. In addition, our data strongly suggest that the motif Leu(496)-Leu(500)-Trp(503) within the β1a C-terminal tail plays a nonessential role in the bidirectional DHPR/RyR1 signaling that supports skeletal-type EC coupling.
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Affiliation(s)
- Jose M Eltit
- the Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, Virgina 23298, and
| | - Clara Franzini-Armstrong
- the Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Claudio F Perez
- From the Department of Anesthesiology Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115,
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7
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Manipulating L-type calcium channels in cardiomyocytes using split-intein protein transsplicing. Proc Natl Acad Sci U S A 2013; 110:15461-6. [PMID: 24003157 DOI: 10.1073/pnas.1308161110] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Manipulating expression of large genes (>6 kb) in adult cardiomyocytes is challenging because these cells are only efficiently transduced by viral vectors with a 4-7 kb packaging capacity. This limitation impedes understanding structure-function mechanisms of important proteins in heart. L-type calcium channels (LTCCs) regulate diverse facets of cardiac physiology including excitation-contraction coupling, excitability, and gene expression. Many important questions about how LTCCs mediate such multidimensional signaling are best resolved by manipulating expression of the 6.6 kb pore-forming α1C-subunit in adult cardiomyocytes. Here, we use split-intein-mediated protein transsplicing to reconstitute LTCC α1C-subunit from two distinct halves, overcoming the difficulty of expressing full-length α1C in cardiomyocytes. Split-intein-tagged α1C fragments encoding dihydropyridine-resistant channels were incorporated into adenovirus and reconstituted in cardiomyocytes. Similar to endogenous LTCCs, recombinant channels targeted to dyads, triggered Ca(2+) transients, associated with caveolin-3, and supported β-adrenergic regulation of excitation-contraction coupling. This approach lowers a longstanding technical hurdle to manipulating large proteins in cardiomyocytes.
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8
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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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9
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Gonzalez C, Contreras GF, Peyser A, Larsson P, Neely A, Latorre R. Voltage sensor of ion channels and enzymes. Biophys Rev 2012; 4:1-15. [PMID: 28509999 PMCID: PMC5425699 DOI: 10.1007/s12551-011-0061-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Accepted: 11/17/2011] [Indexed: 10/14/2022] Open
Abstract
Placed in the cell membrane (a two-dimensional environment), ion channels and enzymes are able to sense voltage. How these proteins are able to detect the difference in the voltage across membranes has attracted much attention, and at times, heated debate during the last few years. Sodium, Ca2+ and K+ voltage-dependent channels have a conserved positively charged transmembrane (S4) segment that moves in response to changes in membrane voltage. In voltage-dependent channels, S4 forms part of a domain that crystallizes as a well-defined structure consisting of the first four transmembrane (S1-S4) segments of the channel-forming protein, which is defined as the voltage sensor domain (VSD). The VSD is tied to a pore domain and VSD movements are allosterically coupled to the pore opening to various degrees, depending on the type of channel. How many charges are moved during channel activation, how much they move, and which are the molecular determinants that mediate the electromechanical coupling between the VSD and the pore domains are some of the questions that we discuss here. The VSD can function, however, as a bona fide proton channel itself, and, furthermore, the VSD can also be a functional part of a voltage-dependent phosphatase.
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Affiliation(s)
- Carlos Gonzalez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Pasaje Harrington 287, Valparaíso, 2360103, Chile
| | - Gustavo F Contreras
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Pasaje Harrington 287, Valparaíso, 2360103, Chile
| | - Alexander Peyser
- Department of Physiology and Biophysics, University of Miami, Miami, FL, USA
| | - Peter Larsson
- Department of Physiology and Biophysics, University of Miami, Miami, FL, USA
| | - Alan Neely
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Pasaje Harrington 287, Valparaíso, 2360103, Chile
| | - Ramón Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Pasaje Harrington 287, Valparaíso, 2360103, Chile.
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10
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Affiliation(s)
- Kurt G Beam
- Department of Physiology and Biophysics, School of Medicine, University of Colorado-Anschutz Medical Campus, Aurora, CO 80045, USA.
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11
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DiFranco M, Tran P, Quiñonez M, Vergara JL. Functional expression of transgenic 1sDHPR channels in adult mammalian skeletal muscle fibres. J Physiol 2011; 589:1421-42. [PMID: 21262876 DOI: 10.1113/jphysiol.2010.202804] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
We investigated the effects of the overexpression of two enhanced green fluorescent protein (EGFP)-tagged α1sDHPR variants on Ca2+ currents (ICa), charge movements (Q) and SR Ca2+ release of muscle fibres isolated from adult mice. Flexor digitorum brevis (FDB)muscles were transfected by in vivo electroporation with plasmids encoding for EGFP-α1sDHPR-wt and EGFP-α1sDHPR-T935Y (an isradipine-insensitive mutant). Two-photon laser scanning microscopy (TPLSM) was used to study the subcellular localization of transgenic proteins, while ICa, Q and Ca2+ release were studied electrophysiologically and optically under voltage-clamp conditions. TPLSM images demonstrated that most of the transgenic α1sDHPR was correctly targeted to the transverse tubular system (TTS). Immunoblotting analysis of crude extracts of transfected fibres demonstrated the synthesis of bona fide transgenic EGFP-α1sDHPR-wt in quantities comparable to that of native α1sDHPR. Though expression of both transgenic variants of the alpha subunit of the dihydropyridine receptor (α1sDHPR) resulted in ∼50% increase in Q, they surprisingly had no effect on the maximal Ca2+ conductance (gCa) nor the SR Ca2+ release. Nonetheless, fibres expressing EGFP-α1sDHPR-T935Y exhibited up to 70% isradipine-insensitive ICa (ICa-ins) with a right-shifted voltage dependence compared to that in control fibres. Interestingly, Qand SRCa2+ release also displayed right-shifted voltage dependence in fibres expressing EGFP-α1sDHPR-T935Y. In contrast, the midpoints of the voltage dependence of gCa, Q and Ca2+ release were not different from those in control fibres and in fibres expressing EGFP-α1sDHPR-wt. Overall, our results suggest that transgenic α1sDHPRs are correctly trafficked and inserted in the TTS membrane, and that a substantial fraction of the mworks as conductive Ca2+ channels capable of physiologically controlling the release of Ca2+ from the SR. A plausible corollary of this work is that the expression of transgenic variants of the α1sDHPR leads to the replacement of native channels interacting with the ryanodine receptor 1 (RyR1), thus demonstrating the feasibility of molecular remodelling of the triads in adult skeletal muscle fibres.
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Affiliation(s)
- Marino DiFranco
- Department of Physiology, David Geffen School of Medicine, UCLA, 10833 Le Conte Avenue, Los Angeles, CA 90095-1751, USA
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Bannister RA, Papadopoulos S, Haarmann CS, Beam KG. Effects of inserting fluorescent proteins into the alpha1S II-III loop: insights into excitation-contraction coupling. ACTA ACUST UNITED AC 2009; 134:35-51. [PMID: 19564426 PMCID: PMC2712974 DOI: 10.1085/jgp.200910241] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
In skeletal muscle, intermolecular communication between the 1,4-dihydropyridine receptor (DHPR) and RYR1 is bidirectional: orthograde coupling (skeletal excitation-contraction coupling) is observed as depolarization-induced Ca(2+) release via RYR1, and retrograde coupling is manifested by increased L-type Ca(2+) current via DHPR. A critical domain (residues 720-765) of the DHPR alpha(1S) II-III loop plays an important but poorly understood role in bidirectional coupling with RYR1. In this study, we examine the consequences of fluorescent protein insertion into different positions within the alpha(1S) II-III loop. In four constructs, a cyan fluorescent protein (CFP)-yellow fluorescent protein (YFP) tandem was introduced in place of residues 672-685 (the peptide A region). All four constructs supported efficient bidirectional coupling as determined by the measurement of L-type current and myoplasmic Ca(2+) transients. In contrast, insertion of a CFP-YFP tandem within the N-terminal portion of the critical domain (between residues 726 and 727) abolished bidirectional signaling. Bidirectional coupling was partially preserved when only a single YFP was inserted between residues 726 and 727. However, insertion of YFP near the C-terminal boundary of the critical domain (between residues 760 and 761) or in the conserved C-terminal portion of the alpha(1S) II-III loop (between residues 785 and 786) eliminated bidirectional coupling. None of the fluorescent protein insertions, even those that interfered with signaling, significantly altered membrane expression or targeting. Thus, bidirectional signaling is ablated by insertions at two different sites in the C-terminal portion of the alpha(1S) II-III loop. Significantly, our results indicate that the conserved portion of the alpha(1S) II-III loop C terminal to the critical domain plays an important role in bidirectional coupling either by conveying conformational changes to the critical domain from other regions of the DHPR or by serving as a site of interaction with other junctional proteins such as RYR1.
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Affiliation(s)
- Roger A Bannister
- Department of Physiology and Biophysics, School of Medicine, University of Colorado Denver, Aurora, CO 80045, USA
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13
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Asadi S, Javan M, Ahmadiani A, Sanati MH. Alternative Splicing in the Synaptic Protein Interaction Site of Rat Cav2.2 (α1B) Calcium Channels: Changes Induced by Chronic Inflammatory Pain. J Mol Neurosci 2009; 39:40-8. [DOI: 10.1007/s12031-008-9159-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2008] [Accepted: 10/27/2008] [Indexed: 10/21/2022]
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14
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Kerr NCH, Holmes FE, Wynick D. Novel mRNA isoforms of the sodium channels Na(v)1.2, Na(v)1.3 and Na(v)1.7 encode predicted two-domain, truncated proteins. Neuroscience 2008; 155:797-808. [PMID: 18675520 DOI: 10.1016/j.neuroscience.2008.04.060] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2007] [Revised: 04/28/2008] [Accepted: 04/28/2008] [Indexed: 12/19/2022]
Abstract
The expression of voltage-gated sodium channels is regulated at multiple levels, and in this study we addressed the potential for alternative splicing of the Na(v)1.2, Na(v)1.3, Na(v)1.6 and Na(v)1.7 mRNAs. We isolated novel mRNA isoforms of Na(v)1.2 and Na(v)1.3 from adult mouse and rat dorsal root ganglia (DRG), Na(v)1.3 and Na(v)1.7 from adult mouse brain, and Na(v)1.7 from neonatal rat brain. These alternatively spliced isoforms introduce an additional exon (Na(v)1.2 exon 17A and topologically equivalent Na(v)1.7 exon 16A) or exon pair (Na(v)1.3 exons 17A and 17B) that contain an in-frame stop codon and result in predicted two-domain, truncated proteins. The mouse and rat orthologous exon sequences are highly conserved (94-100% identities), as are the paralogous Na(v)1.2 and Na(v)1.3 exons (93% identity in mouse) to which the Na(v)1.7 exon has only 60% identity. Previously, Na(v)1.3 mRNA has been shown to be upregulated in rat DRG following peripheral nerve injury, unlike the downregulation of all other sodium channel transcripts. Here we show that the expression of Na(v)1.3 mRNA containing exons 17A and 17B is unchanged in mouse following peripheral nerve injury (axotomy), whereas total Na(v)1.3 mRNA expression is upregulated by 33% (P=0.003), suggesting differential regulation of the alternatively spliced transcripts. The alternatively spliced rodent exon sequences are highly conserved in both the human and chicken genomes, with 77-89% and 72-76% identities to mouse, respectively. The widespread conservation of these sequences strongly suggests an additional level of regulation in the expression of these channels, that is also tissue-specific.
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Affiliation(s)
- N C H Kerr
- Departments of Physiology and Pharmacology, and Clinical Sciences South Bristol, School of Medical Sciences, University of Bristol, Bristol, BS8 1TD, UK
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15
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Bannister RA. Bridging the myoplasmic gap: recent developments in skeletal muscle excitation–contraction coupling. J Muscle Res Cell Motil 2007; 28:275-83. [PMID: 17899404 DOI: 10.1007/s10974-007-9118-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2007] [Accepted: 08/28/2007] [Indexed: 01/17/2023]
Abstract
Conformational coupling between the L-type voltage-gated Ca(2+) channel (or 1,4-dihydropyridine receptor; DHPR) and the ryanodine-sensitive Ca(2+) release channel of the sarcoplasmic reticulum (RyR1) is the mechanistic basis for excitation-contraction (EC) coupling in skeletal muscle. In this article, recent findings regarding the roles of the individual cytoplasmic domains (the amino- and carboxyl-termini, cytoplasmic loops I-II, II-III, and III-IV) of the DHPR alpha(1S) subunit in bi-directional communication with RyR1 will be discussed.
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Affiliation(s)
- Roger A Bannister
- Department of Physiology and Biophysics, School of Medicine, University of Colorado at Denver and Health Sciences Center, RC-1, North Tower, P18-7130, Mail Stop F8307, 12800 E. 19th St, Aurora, CO 80045, USA.
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Sheridan DC, Cheng W, Carbonneau L, Ahern CA, Coronado R. Involvement of a heptad repeat in the carboxyl terminus of the dihydropyridine receptor beta1a subunit in the mechanism of excitation-contraction coupling in skeletal muscle. Biophys J 2005; 87:929-42. [PMID: 15298900 PMCID: PMC1304501 DOI: 10.1529/biophysj.104.043810] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Chimeras consisting of the homologous skeletal dihydropyridine receptor (DHPR) beta1a subunit and the heterologous cardiac/brain beta2a subunit were used to determine which regions of beta1a were responsible for the skeletal-type excitation-contraction (EC) coupling phenotype. Chimeras were transiently transfected in beta1 knockout myotubes and then voltage-clamped with simultaneous measurement of confocal fluo-4 fluorescence. All chimeras expressed a similar density of DHPR charge movements, indicating that the membrane density of DHPR voltage sensors was not a confounding factor in these studies. The data indicates that a beta1a-specific domain present in the carboxyl terminus, namely the D5 region comprising the last 47 residues (beta1a 478-524), is essential for expression of skeletal-type EC coupling. Furthermore, the location of beta1aD5 immediately downstream from conserved domain D4 is also critical. In contrast, chimeras in which beta1aD5 was swapped by the D5 region of beta2a expressed Ca(2+) transients triggered by the Ca(2+) current, or none at all. A hydrophobic heptad repeat is present in domain D5 of beta1a (L478, V485, V492). To determine the role of this motif, residues in the heptad repeat were mutated to alanines. The triple mutant beta1a(L478A/V485A/V492A) recovered weak skeletal-type EC coupling (DeltaF/F(max) = 0.4 +/- 0.1 vs. 2.7 +/- 0.5 for wild-type beta1a). However, a triple mutant with alanine substitutions at positions out of phase with the heptad repeat, beta1a(S481A/L488A/S495A), was normal (DeltaF/F(max) = 2.1 +/- 0.4). In summary, the presence of the beta1a-specific D5 domain, in its correct position after conserved domain D4, is essential for skeletal-type EC coupling. Furthermore, a heptad repeat in beta1aD5 controls the EC coupling activity. The carboxyl terminal heptad repeat of beta1a might be involved in protein-protein interactions with ryanodine receptor type 1 required for DHPR to ryanodine receptor type 1 signal transmission.
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Affiliation(s)
- David C Sheridan
- Department of Physiology, University of Wisconsin School of Medicine, Madison, Wisconsin 53706, USA
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17
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Pohorille A, Schweighofer K, Wilson MA. The origin and early evolution of membrane channels. ASTROBIOLOGY 2005; 5:1-17. [PMID: 15711166 DOI: 10.1089/ast.2005.5.1] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The origin and early evolution of ion channels are considered from the point of view that the transmembrane segments of membrane proteins are structurally quite simple and do not require specific sequences to fold. We argue that the transport of solute species, especially ions, required an early evolution of efficient transport mechanisms, and that the emergence of simple ion channels was protobiologically plausible. We also argue that, despite their simple structure, such channels could possess properties that, at the first sight, appear to require markedly greater complexity. These properties can be subtly modulated by local modifications to the sequence rather than global changes in molecular architecture. In order to address the evolution and development of ion channels, we focus on identifying those protein domains that are commonly associated with ion channel proteins and are conserved throughout the three main domains of life (Eukarya, Bacteria, and Archaea). We discuss the potassium-sodium-calcium superfamily of voltage-gated ion channels, mechanosensitive channels, porins, and ABC-transporters and argue that these families of membrane channels have sufficiently universal architectures that they can readily adapt to the diverse functional demands arising during evolution.
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Affiliation(s)
- Andrew Pohorille
- NASA Ames Research Center, Moffett Field, California 94035, USA.
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18
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Takekura H, Paolini C, Franzini-Armstrong C, Kugler G, Grabner M, Flucher BE. Differential contribution of skeletal and cardiac II-III loop sequences to the assembly of dihydropyridine-receptor arrays in skeletal muscle. Mol Biol Cell 2004; 15:5408-19. [PMID: 15385628 PMCID: PMC532020 DOI: 10.1091/mbc.e04-05-0414] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2004] [Accepted: 09/08/2004] [Indexed: 11/11/2022] Open
Abstract
The plasmalemmal dihydropyridine receptor (DHPR) is the voltage sensor in skeletal muscle excitation-contraction (e-c) coupling. It activates calcium release from the sarcoplasmic reticulum via protein-protein interactions with the ryanodine receptor (RyR). To enable this interaction, DHPRs are arranged in arrays of tetrads opposite RyRs. In the DHPR alpha(1S) subunit, the cytoplasmic loop connecting repeats II and III is a major determinant of skeletal-type e-c coupling. Whether the essential II-III loop sequence (L720-L764) also determines the skeletal-specific arrangement of DHPRs was examined in dysgenic (alpha(1S)-null) myotubes reconstituted with distinct alpha(1) subunit isoforms and II-III loop chimeras. Parallel immunofluorescence and freeze-fracture analysis showed that alpha(1S) and chimeras containing L720-L764, all of which restored skeletal-type e-c coupling, displayed the skeletal arrangement of DHPRs in arrays of tetrads. Conversely, alpha(1C) and those chimeras with a cardiac II-III loop and cardiac e-c coupling properties were targeted into junctional membranes but failed to form tetrads. However, an alpha(1S)-based chimera with the heterologous Musca II-III loop produced tetrads but did not reconstitute skeletal muscle e-c coupling. These findings suggest an inhibitory role in tetrad formation of the cardiac II-III loop and that the organization of DHPRs in tetrads vis-a-vis the RyR is necessary but not sufficient for skeletal-type e-c coupling.
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Affiliation(s)
- Hiroaki Takekura
- Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104, USA
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19
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Page KM, Heblich F, Davies A, Butcher AJ, Leroy J, Bertaso F, Pratt WS, Dolphin AC. Dominant-negative calcium channel suppression by truncated constructs involves a kinase implicated in the unfolded protein response. J Neurosci 2004; 24:5400-9. [PMID: 15190113 PMCID: PMC6729303 DOI: 10.1523/jneurosci.0553-04.2004] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Expression of the calcium channel Ca(V)2.2 is markedly suppressed by coexpression with truncated constructs of Ca(V)2.2. Furthermore, a two-domain construct of Ca(V)2.1 mimicking an episodic ataxia-2 mutation strongly inhibited Ca(V)2.1 currents. We have now determined the specificity of this effect, identified a potential mechanism, and have shown that such constructs also inhibit endogenous calcium currents when transfected into neuronal cell lines. Suppression of calcium channel expression requires interaction between truncated and full-length channels, because there is inter-subfamily specificity. Although there is marked cross-suppression within the Ca(V)2 calcium channel family, there is no cross-suppression between Ca(V)2 and Ca(V)3 channels. The mechanism involves activation of a component of the unfolded protein response, the endoplasmic reticulum resident RNA-dependent kinase (PERK), because it is inhibited by expression of dominant-negative constructs of this kinase. Activation of PERK has been shown previously to cause translational arrest, which has the potential to result in a generalized effect on protein synthesis. In agreement with this, coexpression of the truncated domain I of Ca(V)2.2, together with full-length Ca(V)2.2, reduced the level not only of Ca(V)2.2 protein but also the coexpressed alpha2delta-2. Thapsigargin, which globally activates the unfolded protein response, very markedly suppressed Ca(V)2.2 currents and also reduced the expression level of both Ca(V)2.2 and alpha2delta-2 protein. We propose that voltage-gated calcium channels represent a class of difficult-to-fold transmembrane proteins, in this case misfolding is induced by interaction with a truncated cognate Ca(V) channel. This may represent a mechanism of pathology in episodic ataxia-2.
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Affiliation(s)
- Karen M Page
- Department of Pharmacology, University College London, London WC1E 6BT, United Kingdom
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20
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Papadopoulos S, Leuranguer V, Bannister RA, Beam KG. Mapping sites of potential proximity between the dihydropyridine receptor and RyR1 in muscle using a cyan fluorescent protein-yellow fluorescent protein tandem as a fluorescence resonance energy transfer probe. J Biol Chem 2004; 279:44046-56. [PMID: 15280389 DOI: 10.1074/jbc.m405317200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Excitation-contraction coupling in skeletal muscle involves conformational coupling between the dihydropyridine receptor (DHPR) and the type 1 ryanodine receptor (RyR1) at junctions between the plasma membrane and sarcoplasmic reticulum. In an attempt to find which regions of these proteins are in close proximity to one another, we have constructed a tandem of cyan and yellow fluorescent proteins (CFP and YFP, respectively) linked by a 23-residue spacer, and measured the fluorescence resonance energy transfer (FRET) of the tandem either in free solution or after attachment to sites of the alpha1S and beta1a subunits of the DHPR. For all of the sites examined, attachment of the CFP-YFP tandem did not impair function of the DHPR as a Ca2+ channel or voltage sensor for excitation-contraction coupling. The free tandem displayed a 27.5% FRET efficiency, which decreased significantly after attachment to the DHPR subunits. At several sites examined for both alpha1S (N-terminal, proximal II-III loop of a two fragment construct) and beta1a (C-terminal), the FRET efficiency was similar after expression in either dysgenic (alpha1S-null) or dyspedic (RyR1-null) myotubes. However, compared with dysgenic myotubes, the FRET efficiency in dyspedic myotubes increased from 9.9 to 16.7% for CFP-YFP attached to the N-terminal of beta1a, and from 9.5 to 16.8% for CFP-YFP at the C-terminal of alpha1S. Thus, the tandem reporter suggests that the C terminus of alpha1S and the N terminus of beta1a may be in close proximity to the ryanodine receptor.
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Affiliation(s)
- Symeon Papadopoulos
- Department of Biomedical Sciences, Anatomy Section, Colorado State University, Fort Collins 80523-1617, USA
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21
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Lorenzon NM, Haarmann CS, Norris EE, Papadopoulos S, Beam KG. Metabolic biotinylation as a probe of supramolecular structure of the triad junction in skeletal muscle. J Biol Chem 2004; 279:44057-64. [PMID: 15280388 DOI: 10.1074/jbc.m405318200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Excitation-contraction coupling in skeletal muscle involves conformational coupling between dihydropyridine receptors (DHPRs) in the plasma membrane and ryanodine receptors (RyRs) in the sarcoplasmic reticulum. However, it remains uncertain what regions, if any, of the two proteins interact with one another. Toward this end, it would be valuable to know the spatial interrelationships of DHPRs and RyRs within plasma membrane/sarcoplasmic reticulum junctions. Here we describe a new approach based on metabolic incorporation of biotin into targeted sites of the DHPR. To accomplish this, cDNAs were constructed with a biotin acceptor domain (BAD) fused to selected sites of the DHPR, with fluorescent protein (XFP) attached at a second site. All of the BAD-tagged constructs properly targeted to junctions (as indicted by small puncta of XFP) and were functional for excitation-contraction coupling. To determine whether the introduced BAD was biotinylated and accessible to avidin (approximately 60 kDa), myotubes were fixed, permeablized, and exposed to fluorescently labeled avidin. Upon expression in beta1-null or dysgenic (alpha1S-null) myotubes, punctate avidin fluorescence co-localized with the XFP puncta for BAD attached to the beta1a N- or C-terminals, or the alpha1S N-terminal or II-III loop. However, BAD fused to the alpha1S C-terminal was inaccessible to avidin in dysgenic myotubes (containing RyR1). In contrast, this site was accessible to avidin when the identical construct was expressed in dyspedic myotubes lacking RyR1. These results indicate that avidin has access to a number of sites of the DHPR within fully assembled (RyR1-containing) junctions, but not to the alpha1S C-terminal, which appears to be occluded by the presence of RyR1.
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Affiliation(s)
- Nancy M Lorenzon
- Department of Biomedical Sciences, Anatomy Section, Colorado State University, Fort Collins 80523, USA
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22
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Sheridan DC, Carbonneau L, Ahern CA, Nataraj P, Coronado R. Ca2+-dependent excitation-contraction coupling triggered by the heterologous cardiac/brain DHPR beta2a-subunit in skeletal myotubes. Biophys J 2004; 85:3739-57. [PMID: 14645065 PMCID: PMC1303677 DOI: 10.1016/s0006-3495(03)74790-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Molecular determinants essential for skeletal-type excitation-contraction (EC) coupling have been described in the cytosolic loops of the dihydropyridine receptor (DHPR) alpha1S pore subunit and in the carboxyl terminus of the skeletal-specific DHPR beta1a-subunit. It is unknown whether EC coupling domains present in the beta-subunit influence those present in the pore subunit or if they act independent of each other. To address this question, we investigated the EC coupling signal that is generated when the endogenous DHPR pore subunit alpha1S is paired with the heterologous heart/brain DHPR beta2a-subunit. Studies were conducted in primary cultured myotubes from beta1 knockout (KO), ryanodine receptor type 1 (RyR1) KO, ryanodine receptor type 3 (RyR3) KO, and double RyR1/RyR3 KO mice under voltage clamp with simultaneous monitoring of confocal fluo-4 fluorescence. The beta2a-mediated Ca2+ current recovered in beta1 KO myotubes lacking the endogenous DHPR beta1a-subunit verified formation of the alpha1S/beta1a pair. In myotube genotypes which express no or low-density L-type Ca2+ currents, namely beta1 KO and RyR1 KO, beta2a overexpression recovered a wild-type density of nifedipine-sensitive Ca2+ currents with a slow activation kinetics typical of skeletal myotubes. Concurrent with Ca2+ current recovery, there was a drastic reduction of voltage-dependent, skeletal-type EC coupling and emergence of Ca2+ transients triggered by the Ca2+ current. A comparison of beta2a overexpression in RyR3 KO, RyR1 KO, and double RyR1/RyR3 KO myotubes concluded that both RyR1 and RyR3 isoforms participated in Ca2+-dependent Ca2+ release triggered by the beta2a-subunit. In beta1 KO and RyR1 KO myotubes, the Ca2+-dependent EC coupling promoted by beta2a overexpression had the following characteristics: 1), L-type Ca2+ currents had a wild-type density; 2), Ca2+ transients activated much slower than controls overexpressing beta1a, and the rate of fluorescence increase was consistent with the activation kinetics of the Ca2+ current; 3), the voltage dependence of the Ca2+ transient was bell-shaped and the maximum was centered at approximately +30 mV, consistent with the voltage dependence of the Ca2+ current; and 4), Ca2+ currents and Ca2+ transients were fully blocked by nifedipine. The loss in voltage-dependent EC coupling promoted by beta2a was inferred by the drastic reduction in maximal Ca2+ fluorescence at large positive potentials (DeltaF/Fmax) in double dysgenic/beta1 KO myotubes overexpressing the pore mutant alpha1S (E1014K) and beta2a. The data indicate that beta2a, upon interaction with the skeletal pore subunit alpha1S, overrides critical EC coupling determinants present in alpha1S. We propose that the alpha1S/beta pair, and not the alpha1S-subunit alone, controls the EC coupling signal in skeletal muscle.
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Affiliation(s)
- David C Sheridan
- Department of Physiology, University of Wisconsin, School of Medicine, Madison, Wisconsin 53706, USA
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23
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Avila G, Lee EH, Perez CF, Allen PD, Dirksen RT. FKBP12 binding to RyR1 modulates excitation-contraction coupling in mouse skeletal myotubes. J Biol Chem 2003; 278:22600-8. [PMID: 12704193 DOI: 10.1074/jbc.m205866200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The skeletal muscle sarcoplasmic reticulum (SR) Ca2+ release channel or ryanodine receptor (RyR1) binds four molecules of FKBP12, and the interaction of FKBP12 with RyR1 regulates both unitary and coupled gating of the channel. We have characterized the physiologic effects of previously identified mutations in RyR1 that disrupt FKBP12 binding (V2461G and V2461I) on excitation-contraction (EC) coupling and intracellular Ca2+ homeostasis following their expression in skeletal myotubes derived from RyR1-knockout (dyspedic) mice. Wild-type RyR1-, V246I-, and V2461G-expressing myotubes exhibited similar resting Ca2+ levels and maximal responses to caffeine (10 mm) and cyclopiazonic acid (30 microm). However, maximal voltage-gated Ca2+ release in V2461G-expressing myotubes was reduced by approximately 50% compared with that attributable to wild-type RyR1 (deltaF/Fmax = 1.6 +/- 0.2 and 3.1 +/- 0.4, respectively). Dyspedic myotubes expressing the V2461I mutant protein, that binds FKBP12.6 but not FKBP12, exhibited a comparable reduction in voltage-gated SR Ca2+ release (deltaF/Fmax = 1.0 +/- 0.1). However, voltage-gated Ca2+ release in V2461I-expressing myotubes was restored to a normal level (deltaF/Fmax = 2.9 +/- 0.6) following co-expression of FKBP12.6. None of the mutations that disrupted FKBP binding to RyR1 significantly affected RyR1-mediated enhancement of L-type Ca2+ channel activity (retrograde coupling). These data demonstrate that FKBP12 binding to RyR1 enhances the gain of skeletal muscle EC coupling.
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Affiliation(s)
- Guillermo Avila
- Department of Biochemistry, Cinvestav-IPN, AP 14-740, Mexico City, DF 07000, Mexico
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24
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Haarmann CS, Green D, Casarotto MG, Laver DR, Dulhunty AF. The random-coil 'C' fragment of the dihydropyridine receptor II-III loop can activate or inhibit native skeletal ryanodine receptors. Biochem J 2003; 372:305-16. [PMID: 12620094 PMCID: PMC1223419 DOI: 10.1042/bj20021763] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2002] [Revised: 02/13/2003] [Accepted: 03/06/2003] [Indexed: 11/17/2022]
Abstract
The actions of peptide C, corresponding to (724)Glu-Pro(760) of the II-III loop of the skeletal dihydropyridine receptor, on ryanodine receptor (RyR) channels incorporated into lipid bilayers with the native sarcoplasmic reticulum membrane show that the peptide is a high-affinity activator of native skeletal RyRs at cytoplasmic concentrations of 100 nM-10 microM. In addition, we found that peptide C inhibits RyRs in a voltage-independent manner when added for longer times or at higher concentrations (up to 150 microM). Peptide C had a random-coil structure indicating that it briefly assumes a variety of structures, some of which might activate and others which might inhibit RyRs. The results suggest that RyR activation and inhibition by peptide C arise from independent stochastic processes. A rate constant of 7.5 x 10(5) s(-1).M(-1) was obtained for activation and a lower estimate for the rate constant for inhibition of 5.9 x 10(3) s(-1).M(-1). The combined actions of peptide C and peptide A (II-III loop sequence (671)Thr-Leu(690)) showed that peptide C prevented activation but not blockage of RyRs by peptide A. We suggest that the effects of peptide C indicate functional interactions between a part of the dihydropyridine receptor and the RyR. These interactions could reflect either dynamic changes that occur during excitation-contraction coupling or interactions between the proteins at rest.
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Affiliation(s)
- Claudia S Haarmann
- Muscle Research Group, John Curtin School of Medical Research, Australian National University, P.O. Box 334, Canberra, ACT 2601, Australia
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25
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Ahern CA, Sheridan DC, Cheng W, Mortenson L, Nataraj P, Allen P, De Waard M, Coronado R. Ca2+ current and charge movements in skeletal myotubes promoted by the beta-subunit of the dihydropyridine receptor in the absence of ryanodine receptor type 1. Biophys J 2003; 84:942-59. [PMID: 12547776 PMCID: PMC1302672 DOI: 10.1016/s0006-3495(03)74911-x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The beta-subunit of the dihydropyridine receptor (DHPR) enhances the Ca(2+) channel and voltage-sensing functions of the DHPR. In skeletal myotubes, there is additional modulation of DHPR functions imposed by the presence of ryanodine receptor type-1 (RyR1). Here, we examined the participation of the beta-subunit in the expression of L-type Ca(2+) current and charge movements in RyR1 knock-out (KO), beta1 KO, and double beta1/RyR1 KO myotubes generated by mating heterozygous beta1 KO and RyR1 KO mice. Primary myotube cultures of each genotype were transfected with various beta-isoforms and then whole-cell voltage-clamped for measurements of Ca(2+) and gating currents. Overexpression of the endogenous skeletal beta1a isoform resulted in a low-density Ca(2+) current either in RyR1 KO (36 +/- 9 pS/pF) or in beta1/RyR1 KO (34 +/- 7 pS/pF) myotubes. However, the heterologous beta2a variant with a double cysteine motif in the N-terminus (C3, C4), recovered a Ca(2+) current that was entirely wild-type in density in RyR1 KO (195 +/- 16 pS/pF) and was significantly enhanced in double beta1/RyR1 KO (115 +/- 18 pS/pF) myotubes. Other variants tested from the four beta gene families (beta1a, beta1b, beta1c, beta3, and beta4) were unable to enhance Ca(2+) current expression in RyR1 KO myotubes. In contrast, intramembrane charge movements in beta2a-expressing beta1a/RyR1 KO myotubes were significantly lower than in beta1a-expressing beta1a/RyR1 KO myotubes, and the same tendency was observed in the RyR1 KO myotube. Thus, beta2a had a preferential ability to recover Ca(2+) current, whereas beta1a had a preferential ability to rescue charge movements. Elimination of the double cysteine motif (beta2a C3,4S) eliminated the RyR1-independent Ca(2+) current expression. Furthermore, Ca(2+) current enhancement was observed with a beta2a variant lacking the double cysteine motif and fused to the surface membrane glycoprotein CD8. Thus, tethering the beta2a variant to the myotube surface activated the DHPR Ca(2+) current and bypassed the requirement for RyR1. The data suggest that the Ca(2+) current expressed by the native skeletal DHPR complex has an inherently low density due to inhibitory interactions within the DHPR and that the beta1a-subunit is critically involved in process.
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Affiliation(s)
- Chris A Ahern
- Department of Physiology, University of Wisconsin School of Medicine, Madison, Wisconsin 53706, USA
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26
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Sheridan DC, Cheng W, Ahern CA, Mortenson L, Alsammarae D, Vallejo P, Coronado R. Truncation of the carboxyl terminus of the dihydropyridine receptor beta1a subunit promotes Ca2+ dependent excitation-contraction coupling in skeletal myotubes. Biophys J 2003; 84:220-37. [PMID: 12524277 PMCID: PMC1302605 DOI: 10.1016/s0006-3495(03)74844-9] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
We investigated the contribution of the carboxyl terminus region of the beta1a subunit of the skeletal dihydropyridine receptor (DHPR) to the mechanism of excitation-contraction (EC) coupling. cDNA-transfected beta1 KO myotubes were voltage clamped, and Ca(2+) transients were analyzed by confocal fluo-4 fluorescence. A chimera with an amino terminus half of beta2a and a carboxyl terminus half of beta1a (beta2a 1-287/beta1a 325-524) recapitulates skeletal-type EC coupling quantitatively and was used to generate truncated variants lacking 7 to 60 residues from the beta1a-specific carboxyl terminus (Delta7, Delta21, Delta29, Delta35, and Delta60). Ca(2+) transients recovered by the control chimera have a sigmoidal Ca(2+) fluorescence (DeltaF/F) versus voltage curve with saturation at potentials more positive than +30 mV, independent of external Ca(2+) and stimulus duration. In contrast, the amplitude of Ca(2+) transients expressed by the truncated variants varied with the duration of the pulse, and for Delta29, Delta35, and Delta60, also varied with external Ca(2+) concentration. For Delta7 and Delta21, a 50-ms depolarization produced a sigmoidal DeltaF/F versus voltage curve with a lower than control maximum fluorescence. Moreover, for Delta29, Delta35, and Delta60, a 200-ms depolarization increased the maximum fluorescence and changed the shape of the DeltaF/F versus voltage curve, from sigmoidal to bell-shaped, with a maximum at approximately +30 mV. The change in voltage dependence, together with the external Ca(2+) dependence and additional controls with ryanodine, indicated a loss of skeletal-type EC coupling and the emergence of an EC coupling component triggered by the Ca(2+) current. Analyses of d(DeltaF/F)/dt showed that the rate of cytosolic Ca(2+) increase during the Ca(2+) transient was fivefold faster for the control chimera than for the severely truncated variants (Delta29, Delta35, and Delta60) and was consistent with the kinetics of the DHPR Ca(2+) current. In summary, absence of the beta1a-specific carboxyl terminus (last 29 to 60 residues of the control chimera) results in a loss of the fast component of the Ca(2+) transient, bending of the DeltaF/F versus voltage curve, and emergence of EC coupling triggered by the Ca(2+) current. The studies underscore the essential role of the carboxyl terminus region of the DHPR beta1a subunit in fast voltage dependent EC coupling in skeletal myotubes.
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Affiliation(s)
- David C Sheridan
- Department of Physiology, University of Wisconsin School of Medicine, Madison, 53706, USA
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27
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Arikkath J, Felix R, Ahern C, Chen CC, Mori Y, Song I, Shin HS, Coronado R, Campbell KP. Molecular characterization of a two-domain form of the neuronal voltage-gated P/Q-type calcium channel alpha(1)2.1 subunit. FEBS Lett 2002; 532:300-8. [PMID: 12482583 DOI: 10.1016/s0014-5793(02)03693-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We characterized the neuronal two-domain (95kD-alpha(1)2.1) form of the alpha(1)2.1 subunit of the voltage-gated calcium channels using genetic and molecular analysis. The 95kD-alpha(1)2.1 is absent in neuronal preparations from CACNA1A null mouse demonstrating that alpha(1)2.1 and 95kD-alpha(1)2.1 arise from the same gene. A recombinant two-domain form (alpha(1AI-II)) of alpha(1)2.1 associates with the beta subunit and is trafficked to the plasma membrane. Translocation of the alpha(1AI-II) to the plasma membrane requires association with the beta subunit, since a mutation in the alpha(1AI-II) that inhibits beta subunit association reduces membrane trafficking. Though the alpha(1AI-II) protein does not conduct any voltage-gated currents, we have previously shown that it generates a high density of non-linear charge movements [Ahern et al., Proc. Natl. Acad. Sci. USA 98 (2001) 6935-6940]. In this study, we demonstrate that co-expression of the alpha(1AI-II) significantly reduces the current amplitude of alpha(1)2.1/beta(1a)/alpha(2)delta channels, via competition for the beta subunit. Taken together, our results demonstrate a dual functional role for the alpha(1AI-II) protein, both as a voltage sensor and modulator of P/Q-type currents in recombinant systems. These studies suggest an in vivo role for the 95kD-alpha(1)2.1 in altering synaptic activity via protein-protein interactions and/or regulation of P/Q-type currents.
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Affiliation(s)
- Jyothi Arikkath
- Howard Hughes Medical Institute, Department of Physiology, University of Iowa College of Medicine, 400 Eckstein Medical Research Building, Iowa City, IA 52242-1101, USA
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28
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Abstract
The ryanodine receptors (RyRs) are a family of Ca2+ release channels found on intracellular Ca2+ storage/release organelles. The RyR channels are ubiquitously expressed in many types of cells and participate in a variety of important Ca2+ signaling phenomena (neurotransmission, secretion, etc.). In striated muscle, the RyR channels represent the primary pathway for Ca2+ release during the excitation-contraction coupling process. In general, the signals that activate the RyR channels are known (e.g., sarcolemmal Ca2+ influx or depolarization), but the specific mechanisms involved are still being debated. The signals that modulate and/or turn off the RyR channels remain ambiguous and the mechanisms involved unclear. Over the last decade, studies of RyR-mediated Ca2+ release have taken many forms and have steadily advanced our knowledge. This robust field, however, is not without controversial ideas and contradictory results. Controversies surrounding the complex Ca2+ regulation of single RyR channels receive particular attention here. In addition, a large body of information is synthesized into a focused perspective of single RyR channel function. The present status of the single RyR channel field and its likely future directions are also discussed.
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Affiliation(s)
- Michael Fill
- Department of Physiology, Loyola University Chicago, Maywood, Illinois 60153, USA
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Flucher BE, Weiss RG, Grabner M. Cooperation of two-domain Ca(2+) channel fragments in triad targeting and restoration of excitation- contraction coupling in skeletal muscle. Proc Natl Acad Sci U S A 2002; 99:10167-72. [PMID: 12119388 PMCID: PMC126642 DOI: 10.1073/pnas.122345799] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The specific incorporation of the skeletal muscle voltage-dependent Ca(2+) channel in the triad is a prerequisite of normal excitation-contraction (EC) coupling. Sequences involved in membrane expression and in targeting of Ca(2+) channels into skeletal muscle triads have been described in different regions of the alpha(1S) subunit. Here we studied the targeting properties of two-domain alpha(1S) fragments, green fluorescent protein (GFP)-I x II (1-670) and III x IV (691-1873) expressed alone or in combination in dysgenic (alpha(1S)-null) myotubes. Immunofluorescence analysis showed that GFP-I x II or III x IV expressed separately were not targeted into triads. In contrast, on coexpression the two alpha(1S) fragments were colocalized with one another and with the ryanodine receptor in the triads. Coexpression of GFP-I x II and III x IV also fully restored Ca(2+) currents and depolarization-induced Ca(2+) transients, despite the severed connection between the two channel halves and the absence of amino acids 671-690 from either alpha(1S) fragment. Thus, triad targeting, like the rescue of function, requires the cooperation and coassembly of the two complementary channel fragments. Transferring the C terminus of alpha(1S) to the N-terminal two-domain fragment (GFP-I x II x tail), or transferring the I-II connecting loop containing the beta interaction domain to the C-terminal fragment (III x IV x beta in) did not improve the targeting properties of the individually expressed two-domain channel fragments. Thus, the cooperation of GFP-I.II and III.IV in targeting cannot be explained solely by a sequential action of the beta subunit by means of the I-II loop in releasing the channel from the sarcoplasmic reticulum and of the C terminus in triad targeting.
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Affiliation(s)
- Bernhard E Flucher
- Department of Physiology, University of Innsbruck, A-6020 Innsbruck, Austria.
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Dulhunty AF, Haarmann CS, Green D, Laver DR, Board PG, Casarotto MG. Interactions between dihydropyridine receptors and ryanodine receptors in striated muscle. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2002; 79:45-75. [PMID: 12225776 DOI: 10.1016/s0079-6107(02)00013-5] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Excitation-contraction coupling in both skeletal and cardiac muscle depends on structural and functional interactions between the voltage-sensing dihydropyridine receptor L-type Ca(2+) channels in the surface/transverse tubular membrane and ryanodine receptor Ca(2+) release channels in the sarcoplasmic reticulum membrane. The channels are targeted to either side of a narrow junctional gap that separates the external and internal membrane systems and are arranged so that bi-directional structural and functional coupling can occur between the proteins. There is strong evidence for a physical interaction between the two types of channel protein in skeletal muscle. This evidence is derived from studies of excitation-contraction coupling in intact myocytes and from experiments in isolated systems where fragments of the dihydropyridine receptor can bind to the ryanodine receptors in sarcoplasmic reticulum vesicles or in lipid bilayers and alter channel activity. Although micro-regions that participate in the functional interactions have been identified in each protein, the role of these regions and the molecular nature of the protein-protein interaction remain unknown. The trigger for Ca(2+) release through ryanodine receptors in cardiac muscle is a Ca(2+) influx through the L-type Ca(2+) channel. The Ca(2+) entering through the surface membrane Ca(2+) channels flows directly onto underlying ryanodine receptors and activates the channels. This was thought to be a relatively simple system compared with that in skeletal muscle. However, complexities are emerging and evidence has now been obtained for a bi-directional physical coupling between the proteins in cardiac as well as skeletal muscle. The molecular nature of this coupling remains to be elucidated.
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Affiliation(s)
- A F Dulhunty
- John Curtin School of Medical Research, Australian National University, P.O. Box 334 2601 Canberra, Australia.
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31
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Yamamoto T, Ikemoto N. T-tubule depolarization-induced local events in the ryanodine receptor, as monitored with the fluorescent conformational probe incorporated by mediation of peptide A. J Biol Chem 2002; 277:984-92. [PMID: 11682466 DOI: 10.1074/jbc.m102347200] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
There is a considerable controversy about the postulated role of the Thr(671)-Leu(690) (peptide A) region of the dihydropyridine (DHP) receptor alpha1 II-III loop. Here we report that peptide A introduced the fluorescence probe methyl coumarin acetamido (MCA) in a well defined region of the ryanodine receptor (RyR), A-site, in a specific manner. Depolarization of the T-tubule moiety of the triad induced a rapid increase of the fluorescence intensity of the MCA attached to the A-site. Other RyR agonists, which activate the RyR without mediation of the DHP receptor (e.g. caffeine, polylysine, and peptide A), induced Ca(2+) release without producing such an MCA fluorescence increase. Both magnitudes of the fluorescence change and Ca(2+) release increased with the increase in the degree of T-tubule depolarization. MCA fluorescence increase at the A-site and subsequent sarcoplasmic reticulum Ca(2+) release were blocked by blocking of the DHP receptor-to-RyR communication. These results may be accounted for by two alternative models as follows. (a) Upon T-tubule depolarization a portion of the DHP receptor comes close to the RyR, forming a hydrophobic interface (within such an interface the A-site is located), or (b) T-tubule depolarization may produce a local conformational change in the A-site-containing region of the RyR that is not necessarily within the DHP receptor/RyR junction.
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Affiliation(s)
- Takeshi Yamamoto
- Boston Biomedical Research Institute, Watertown, Massachusetts 02472, USA
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Yamamoto T, Rodriguez J, Ikemoto N. Ca2+-dependent dual functions of peptide C. The peptide corresponding to the Glu724-Pro760 region (the so-called determinant of excitation-contraction coupling) of the dihydropyridine receptor alpha 1 subunit II-III loop. J Biol Chem 2002; 277:993-1001. [PMID: 11682472 DOI: 10.1074/jbc.m105837200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Both in vivo and in vitro studies suggest that the Glu(724)-Pro(760) (peptide C) region of the dihydropyridine receptor alpha1 II-III loop is important for excitation-contraction coupling, although its actual function has not yet been elucidated. According to our recent studies, peptide C inhibits Ca(2+) release induced by T-tubule depolarization or peptide A. Here we report that peptide C has Ca(2+)-dependent dual functions on the skeletal muscle ryanodine receptor. Thus, at above-threshold [Ca(2+)]s (> or =0.1 microm) peptide C blocked peptide A-induced activation of the ryanodine receptor (ryanodine binding and Ca(2+) release); peptide C also blocked T-tubule depolarization-induced Ca(2+) release. However, at sub-threshold [Ca(2+)]s (<0.1 microm), peptide C enhanced ryanodine binding and induced Ca(2+) release. If peptide A was present, together with peptide C, both peptides produced additive activation effects. Neither peptide A nor peptide C produced any appreciable effect on the cardiac muscle ryanodine receptor at both high (1.0 microm) and low (0.01 microm) Ca(2+) concentrations. These results suggest the possibility that the in vivo counterpart of peptide C retains both activating and blocking functions of the skeletal muscle-type excitation-contraction coupling.
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Affiliation(s)
- Takeshi Yamamoto
- Boston Biomedical Research Institute, Watertown, Massachusetts 02472, USA
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Ahern CA, Vallejo P, Mortenson L, Coronado R. Functional analysis of a frame-shift mutant of the dihydropyridine receptor pore subunit (alpha1S) expressing two complementary protein fragments. BMC PHYSIOLOGY 2001; 1:15. [PMID: 11806762 PMCID: PMC64647 DOI: 10.1186/1472-6793-1-15] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/09/2001] [Accepted: 12/31/2001] [Indexed: 11/30/2022]
Abstract
BACKGROUND The L-type Ca2+ channel formed by the dihydropyridine receptor (DHPR) of skeletal muscle senses the membrane voltage and opens the ryanodine receptor (RyR1). This channel-to-channel coupling is essential for Ca2+ signaling but poorly understood. We characterized a single-base frame-shift mutant of alpha1S, the pore subunit of the DHPR, that has the unusual ability to function voltage sensor for excitation-contraction (EC) coupling by virtue of expressing two complementary hemi-Ca2+ channel fragments. RESULTS Functional analysis of cDNA transfected dysgenic myotubes lacking alpha1S were carried out using voltage-clamp, confocal Ca2+ indicator fluoresence, epitope immunofluorescence and immunoblots of expressed proteins. The frame-shift mutant (fs-alpha1S) expressed the N-terminal half of alpha1S (M1 to L670) and the C-terminal half starting at M701 separately. The C-terminal fragment was generated by an unexpected restart of translation of the fs-alpha1S message at M701 and was eliminated by a M701I mutation. Protein-protein complementation between the two fragments produced recovery of skeletal-type EC coupling but not L-type Ca2+ current. DISCUSSION A premature stop codon in the II-III loop may not necessarily cause a loss of DHPR function due to a restart of translation within the II-III loop, presumably by a mechanism involving leaky ribosomal scanning. In these cases, function is recovered by expression of complementary protein fragments from the same cDNA. DHPR-RyR1 interactions can be achieved via protein-protein complementation between hemi-Ca2+ channel proteins, hence an intact II-III loop is not essential for coupling the DHPR voltage sensor to the opening of RyR1 channel.
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Affiliation(s)
- Chris A Ahern
- Department of Physiology, University of Wisconsin School of Medicine, Madison, WI 53706, USA
| | - Paola Vallejo
- Department of Physiology, University of Wisconsin School of Medicine, Madison, WI 53706, USA
| | - Lindsay Mortenson
- Department of Physiology, University of Wisconsin School of Medicine, Madison, WI 53706, USA
| | - Roberto Coronado
- Department of Physiology, University of Wisconsin School of Medicine, Madison, WI 53706, USA
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Dominant-negative synthesis suppression of voltage-gated calcium channel Cav2.2 induced by truncated constructs. J Neurosci 2001. [PMID: 11606638 DOI: 10.1523/jneurosci.21-21-08495.2001] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Voltage-gated calcium channel alpha1 subunits consist of four domains (I-IV), each with six transmembrane segments. A number of truncated isoforms have been identified to occur as a result of alternative splicing or mutation. We have examined the functional consequences for expression of full-length Ca(v)2.2 (alpha1B) of its coexpression with truncated constructs of Ca(v)2.2. Domains I-II or domains III-IV, when expressed individually, together with the accessory subunits beta1b and alpha2delta-1, did not form functional channels. When they were coexpressed, low-density whole-cell currents and functional channels with properties similar to wild-type channels were observed. However, when domain I-II, domain III-IV, or domain I alone were coexpressed with full-length Ca(v)2.2, they markedly suppressed its functional expression, although at the single channel level, when channels were recorded, there were no differences in their biophysical properties. Furthermore, when it was coexpressed with either domain I-II or domain I, the fluorescence of green fluorescent protein (GFP)-Ca(v)2.2 and expression of Ca(v)2.2 protein was almost abolished. Suppression does not involve sequestration of the Ca(v)beta subunit, because loss of GFP-Ca(v)2.2 expression also occurred in the absence of beta subunit, and the effect of domain I-II or domain I could not be mimicked by the cytoplasmic I-II loop of Ca(v)2.2. It requires transmembrane segments, because the isolated Ca(v)2.2 N terminus did not have any effect. Our results indicate that the mechanism of suppression of Ca(v)2.2 by truncated constructs containing domain I involves inhibition of channel synthesis, which may represent a role of endogenously expressed truncated Ca(v) isoforms.
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Ahern CA, Bhattacharya D, Mortenson L, Coronado R. A component of excitation-contraction coupling triggered in the absence of the T671-L690 and L720-Q765 regions of the II-III loop of the dihydropyridine receptor alpha(1s) pore subunit. Biophys J 2001; 81:3294-307. [PMID: 11720993 PMCID: PMC1301787 DOI: 10.1016/s0006-3495(01)75963-2] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
We conducted a deletion analysis of two regions identified in the II-III loop of alpha(1S), residues 671-690, which were shown to bind to ryanodine receptor type 1 (RyR1) and stimulate RyR1 channels in vitro, and residues 720-765 or the narrower 724-743 region, which confer excitation-contraction (EC) coupling function to chimeric dihydropyridine receptors (DHPRs). Deletion mutants were expressed in dysgenic alpha(1S)-null myotubes and analyzed by voltage-clamp and confocal fluo-4 fluorescence. Immunostaining of the mutant subunits using an N-terminus tag revealed abundant protein expression in all cases. Furthermore, the maximum recovered charge movement density was >80% of that recovered by full-length alpha(1S) in all cases. Delta671-690 had no effect on the magnitude of voltage-evoked Ca(2+) transients or the L-type Ca(2+) current density. In contrast, Delta720-765 or Delta724-743 abolished Ca(2+) transients entirely, and L-type Ca(2+) current was reduced or absent. Surprisingly, Ca(2+) transients and Ca(2+) currents of a moderate magnitude were recovered by the double deletion mutant Delta671-690/Delta720-765. A simple explanation for this result is that Delta720-765 induces a conformation change that disrupts EC coupling, and this conformational change is partially reverted by Delta671-690. To test for Ca(2+)-entry independent EC coupling, a pore mutation (E1014K) known to entirely abolish the inward Ca(2+) current was introduced. alpha(1S) Delta671-690/Delta720-765/E1014K expressed Ca(2+) transients with Boltzmann parameters identical to those of the Ca(2+)-conducting double deletion construct. The data strongly suggest that skeletal-type EC coupling is not uniquely controlled by alpha(1S) 720-765. Other regions of alpha(1S) or other DHPR subunits must therefore directly contribute to the activation of RyR1 during EC coupling.
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Affiliation(s)
- C A Ahern
- Department of Physiology, University of Wisconsin School of Medicine, Madison, Wisconsin 53706, USA
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Raghib A, Bertaso F, Davies A, Page KM, Meir A, Bogdanov Y, Dolphin AC. Dominant-negative synthesis suppression of voltage-gated calcium channel Cav2.2 induced by truncated constructs. J Neurosci 2001; 21:8495-504. [PMID: 11606638 PMCID: PMC6762802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2001] [Revised: 08/15/2001] [Accepted: 08/23/2001] [Indexed: 02/21/2023] Open
Abstract
Voltage-gated calcium channel alpha1 subunits consist of four domains (I-IV), each with six transmembrane segments. A number of truncated isoforms have been identified to occur as a result of alternative splicing or mutation. We have examined the functional consequences for expression of full-length Ca(v)2.2 (alpha1B) of its coexpression with truncated constructs of Ca(v)2.2. Domains I-II or domains III-IV, when expressed individually, together with the accessory subunits beta1b and alpha2delta-1, did not form functional channels. When they were coexpressed, low-density whole-cell currents and functional channels with properties similar to wild-type channels were observed. However, when domain I-II, domain III-IV, or domain I alone were coexpressed with full-length Ca(v)2.2, they markedly suppressed its functional expression, although at the single channel level, when channels were recorded, there were no differences in their biophysical properties. Furthermore, when it was coexpressed with either domain I-II or domain I, the fluorescence of green fluorescent protein (GFP)-Ca(v)2.2 and expression of Ca(v)2.2 protein was almost abolished. Suppression does not involve sequestration of the Ca(v)beta subunit, because loss of GFP-Ca(v)2.2 expression also occurred in the absence of beta subunit, and the effect of domain I-II or domain I could not be mimicked by the cytoplasmic I-II loop of Ca(v)2.2. It requires transmembrane segments, because the isolated Ca(v)2.2 N terminus did not have any effect. Our results indicate that the mechanism of suppression of Ca(v)2.2 by truncated constructs containing domain I involves inhibition of channel synthesis, which may represent a role of endogenously expressed truncated Ca(v) isoforms.
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Affiliation(s)
- A Raghib
- Department of Pharmacology, University College London, London WC1E6BT, United Kingdom
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37
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Ahern CA, Powers PA, Biddlecome GH, Roethe L, Vallejo P, Mortenson L, Strube C, Campbell KP, Coronado R, Gregg RG. Modulation of L-type Ca2+ current but not activation of Ca2+ release by the gamma1 subunit of the dihydropyridine receptor of skeletal muscle. BMC PHYSIOLOGY 2001; 1:8. [PMID: 11495636 PMCID: PMC37314 DOI: 10.1186/1472-6793-1-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/23/2001] [Accepted: 07/24/2001] [Indexed: 11/25/2022]
Abstract
BACKGROUND The multisubunit (alpha1S,alpha2-delta, beta1a and gamma1) skeletal muscle dihydropyridine receptor (DHPR) transduces membrane depolarization into release of Ca2+ from the sarcoplasmic reticulum (SR) and also acts as an L-type Ca2+ channel. To more fully investigate the function of the gamma1 subunit in these two processes, we produced mice lacking this subunit by gene targeting. RESULTS Mice lacking the DHPR gamma1 subunit (gamma1 null) survive to adulthood, are fertile and have no obvious gross phenotypic abnormalities. The gamma1 subunit is expressed at approximately half the normal level in heterozygous mice (gamma1 het). The density of the L-type Ca2+ current in gamma1 null and gamma1 het myotubes was higher than in controls. Inactivation of the Ca2+ current produced by a long depolarization was slower and incomplete in gamma1 null and gamma1 het myotubes, and was shifted to a more positive potential than in controls. However, the half-activation potential of intramembrane charge movements was not shifted, and the maximum density of the total charge was unchanged. Also, no shift was observed in the voltage-dependence of Ca2+ transients. gamma1 null and gamma1 het myotubes had the same peak Ca2+ amplitude vs. voltage relationship as control myotubes. CONCLUSIONS The L-type Ca2+ channel function, but not the SR Ca2+ release triggering function of the skeletal muscle dihydropyridine receptor, is modulated by the gamma1 subunit.
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Affiliation(s)
- Chris A Ahern
- Department of Physiology, University of Wisconsin School of Medicine, and
| | - Patricia A Powers
- Biotechnology Center, University of Wisconsin, Madison, WI, 53706, USA
| | - Gloria H Biddlecome
- Howard Hughes Medical Institute, and
- Departments of Physiology and Biophysics, and Neurology, The University of Iowa College of Medicine, Iowa City, IA, 52242, USA
| | - Laura Roethe
- Biotechnology Center, University of Wisconsin, Madison, WI, 53706, USA
| | - Paola Vallejo
- Department of Physiology, University of Wisconsin School of Medicine, and
| | - Lindsay Mortenson
- Department of Physiology, University of Wisconsin School of Medicine, and
| | - Caroline Strube
- Laboratoire de Physiologie des Elements Excitables, Universite Claude Bernard - Lyon 1, France; and
| | - Kevin P Campbell
- Howard Hughes Medical Institute, and
- Departments of Physiology and Biophysics, and Neurology, The University of Iowa College of Medicine, Iowa City, IA, 52242, USA
| | - Roberto Coronado
- Department of Physiology, University of Wisconsin School of Medicine, and
| | - Ronald G Gregg
- Department of Biochemistry and Molecular Biology, and Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, 40202, USA
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