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Stac Proteins Suppress Ca 2+-Dependent Inactivation of Neuronal l-type Ca 2+ Channels. J Neurosci 2018; 38:9215-9227. [PMID: 30201773 DOI: 10.1523/jneurosci.0695-18.2018] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 08/30/2018] [Accepted: 09/01/2018] [Indexed: 01/28/2023] Open
Abstract
Stac protein (named for its SH3- and cysteine-rich domains) was first identified in brain 20 years ago and is currently known to have three isoforms. Stac2, Stac1, and Stac3 transcripts are found at high, modest, and very low levels, respectively, in the cerebellum and forebrain, but their neuronal functions have been little investigated. Here, we tested the effects of Stac proteins on neuronal, high-voltage-activated Ca2+ channels. Overexpression of the three Stac isoforms eliminated Ca2+-dependent inactivation (CDI) of l-type current in rat neonatal hippocampal neurons (sex unknown), but not CDI of non-l-type current. Using heterologous expression in tsA201 cells (together with β and α2-δ1 auxiliary subunits), we found that CDI for CaV1.2 and CaV1.3 (the predominant, neuronal l-type Ca2+ channels) was suppressed by all three Stac isoforms, whereas CDI for the P/Q channel, CaV2.1, was not. For CaV1.2, the inhibition of CDI by the Stac proteins appeared to involve their direct interaction with the channel's C terminus. Within the Stac proteins, a weakly conserved segment containing ∼100 residues and linking the structurally conserved PKC C1 and SH3_1 domains was sufficient to fully suppress CDI. The presence of CDI for l-type current in control neonatal neurons raised the possibility that endogenous Stac levels are low in these neurons and Western blotting indicated that the expression of Stac2 was substantially increased in adult forebrain and cerebellum compared with neonate. Together, our results indicate that one likely function of neuronal Stac proteins is to tune Ca2+ entry via neuronal l-type channels.SIGNIFICANCE STATEMENT Stac protein, first identified 20 years ago in brain, has recently been found to be essential for proper trafficking and function of the skeletal muscle l-type Ca2+ channel and is the site of mutations causing a severe, inherited human myopathy. In neurons, however, functions for Stac protein have remained unexplored. Here, we report that one likely function of neuronal Stac proteins is tuning Ca2+ entry via l-type, but not that via non-l-type, Ca2+ channels. Moreover, there is a large postnatal increase in protein levels of the major neuronal isoform (Stac2) in forebrain and cerebellum, which could provide developmental regulation of l-type channel Ca2+ signaling in these brain regions.
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2
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Transcriptional profiling of rat skeletal muscle hypertrophy under restriction of blood flow. Gene 2016; 594:229-237. [PMID: 27613141 DOI: 10.1016/j.gene.2016.09.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 08/16/2016] [Accepted: 09/05/2016] [Indexed: 01/03/2023]
Abstract
Blood flow restriction (BFR) under low-intensity resistance training (LIRT) can produce similar effects upon muscles to that of high-intensity resistance training (HIRT) while overcoming many of the restrictions to HIRT that occurs in a clinical setting. However, the potential molecular mechanisms of BFR induced muscle hypertrophy remain largely unknown. Here, using a BFR rat model, we aim to better elucidate the mechanisms regulating muscle hypertrophy as induced by BFR and reveal possible clinical therapeutic targets for atrophy cases. We performed genome wide screening with microarray analysis to identify unique differentially expressed genes during rat muscle hypertrophy. We then successfully separated the differentially expressed genes from BRF treated soleus samples by comparing the Affymetrix rat Genome U34 2.0 array with the control. Using qRT-PCR and immunohistochemistry (IHC) we also analyzed other related differentially expressed genes. Results suggested that muscle hypertrophy induced by BFR is essentially regulated by the rate of protein turnover. Specifically, PI3K/AKT and MAPK pathways act as positive regulators in controlling protein synthesis where ubiquitin-proteasome acts as a negative regulator. This represents the first general genome wide level investigation of the gene expression profile in the rat soleus after BFR treatment. This may aid our understanding of the molecular mechanisms regulating and controlling muscle hypertrophy and provide support to the BFR strategies aiming to prevent muscle atrophy in a clinical setting.
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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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Beqollari D, Romberg CF, Filipova D, Meza U, Papadopoulos S, Bannister RA. Rem uncouples excitation-contraction coupling in adult skeletal muscle fibers. ACTA ACUST UNITED AC 2015; 146:97-108. [PMID: 26078055 PMCID: PMC4485024 DOI: 10.1085/jgp.201411314] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Accepted: 05/18/2015] [Indexed: 12/14/2022]
Abstract
The RGK protein Rem uncouples the voltage sensors of CaV1.1 from RYR1-mediated sarcoplasmic reticulum Ca2+ release via its ability to interact with the auxiliary β1a subunit. In skeletal muscle, excitation–contraction (EC) coupling requires depolarization-induced conformational rearrangements in L-type Ca2+ channel (CaV1.1) to be communicated to the type 1 ryanodine-sensitive Ca2+ release channel (RYR1) of the sarcoplasmic reticulum (SR) via transient protein–protein interactions. Although the molecular mechanism that underlies conformational coupling between CaV1.1 and RYR1 has been investigated intensely for more than 25 years, the question of whether such signaling occurs via a direct interaction between the principal, voltage-sensing α1S subunit of CaV1.1 and RYR1 or through an intermediary protein persists. A substantial body of evidence supports the idea that the auxiliary β1a subunit of CaV1.1 is a conduit for this intermolecular communication. However, a direct role for β1a has been difficult to test because β1a serves two other functions that are prerequisite for conformational coupling between CaV1.1 and RYR1. Specifically, β1a promotes efficient membrane expression of CaV1.1 and facilitates the tetradic ultrastructural arrangement of CaV1.1 channels within plasma membrane–SR junctions. In this paper, we demonstrate that overexpression of the RGK protein Rem, an established β subunit–interacting protein, in adult mouse flexor digitorum brevis fibers markedly reduces voltage-induced myoplasmic Ca2+ transients without greatly affecting CaV1.1 targeting, intramembrane gating charge movement, or releasable SR Ca2+ store content. In contrast, a β1a-binding–deficient Rem triple mutant (R200A/L227A/H229A) has little effect on myoplasmic Ca2+ release in response to membrane depolarization. Thus, Rem effectively uncouples the voltage sensors of CaV1.1 from RYR1-mediated SR Ca2+ release via its ability to interact with β1a. Our findings reveal Rem-expressing adult muscle as an experimental system that may prove useful in the definition of the precise role of the β1a subunit in skeletal-type EC coupling.
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Affiliation(s)
- Donald Beqollari
- Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO 80045
| | - Christin F Romberg
- Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO 80045
| | - Dilyana Filipova
- Institute of Vegetative Physiology, University Hospital of Köln, D-50931 Köln, Germany
| | - Ulises Meza
- Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO 80045 Departamento de Fisiología y Biofísica, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, 78210 San Luis Potosí, Mexico
| | - Symeon Papadopoulos
- Institute of Vegetative Physiology, University Hospital of Köln, D-50931 Köln, Germany
| | - Roger A Bannister
- Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO 80045
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5
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Stac adaptor proteins regulate trafficking and function of muscle and neuronal L-type Ca2+ channels. Proc Natl Acad Sci U S A 2014; 112:602-6. [PMID: 25548159 DOI: 10.1073/pnas.1423113112] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Excitation-contraction (EC) coupling in skeletal muscle depends upon trafficking of CaV1.1, the principal subunit of the dihydropyridine receptor (DHPR) (L-type Ca(2+) channel), to plasma membrane regions at which the DHPRs interact with type 1 ryanodine receptors (RyR1) in the sarcoplasmic reticulum. A distinctive feature of this trafficking is that CaV1.1 expresses poorly or not at all in mammalian cells that are not of muscle origin (e.g., tsA201 cells), in which all of the other nine CaV isoforms have been successfully expressed. Here, we tested whether plasma membrane trafficking of CaV1.1 in tsA201 cells is promoted by the adapter protein Stac3, because recent work has shown that genetic deletion of Stac3 in skeletal muscle causes the loss of EC coupling. Using fluorescently tagged constructs, we found that Stac3 and CaV1.1 traffic together to the tsA201 plasma membrane, whereas CaV1.1 is retained intracellularly when Stac3 is absent. Moreover, L-type Ca(2+) channel function in tsA201 cells coexpressing Stac3 and CaV1.1 is quantitatively similar to that in myotubes, despite the absence of RyR1. Although Stac3 is not required for surface expression of CaV1.2, the principle subunit of the cardiac/brain L-type Ca(2+) channel, Stac3 does bind to CaV1.2 and, as a result, greatly slows the rate of current inactivation, with Stac2 acting similarly. Overall, these results indicate that Stac3 is an essential chaperone of CaV1.1 in skeletal muscle and that in the brain, Stac2 and Stac3 may significantly modulate CaV1.2 function.
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Taylor J, Pereyra A, Zhang T, Messi ML, Wang ZM, Hereñú C, Kuan PF, Delbono O. The Cavβ1a subunit regulates gene expression and suppresses myogenin in muscle progenitor cells. ACTA ACUST UNITED AC 2014; 205:829-46. [PMID: 24934157 PMCID: PMC4068134 DOI: 10.1083/jcb.201403021] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Cavβ1a acts as a voltage-gated calcium channel-independent regulator of gene expression in muscle progenitor cells and is required for their normal expansion during myogenic development. Voltage-gated calcium channel (Cav) β subunits are auxiliary subunits to Cavs. Recent reports show Cavβ subunits may enter the nucleus and suggest a role in transcriptional regulation, but the physiological relevance of this localization remains unclear. We sought to define the nuclear function of Cavβ in muscle progenitor cells (MPCs). We found that Cavβ1a is expressed in proliferating MPCs, before expression of the calcium conducting subunit Cav1.1, and enters the nucleus. Loss of Cavβ1a expression impaired MPC expansion in vitro and in vivo and caused widespread changes in global gene expression, including up-regulation of myogenin. Additionally, we found that Cavβ1a localizes to the promoter region of a number of genes, preferentially at noncanonical (NC) E-box sites. Cavβ1a binds to a region of the Myog promoter containing an NC E-box, suggesting a mechanism for inhibition of myogenin gene expression. This work indicates that Cavβ1a acts as a Cav-independent regulator of gene expression in MPCs, and is required for their normal expansion during myogenic development.
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Affiliation(s)
- Jackson Taylor
- Department of Internal Medicine-Gerontology, Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC 27157Department of Internal Medicine-Gerontology, Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Andrea Pereyra
- Department of Internal Medicine-Gerontology, Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC 27157 Biochemistry Research Institute of La Plata (INIBIOLP)/National Scientific and Technical Research Council (CONICET), School of Medicine, National University of La Plata, 1900 La Plata, BA, Argentina
| | - Tan Zhang
- Department of Internal Medicine-Gerontology, Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Maria Laura Messi
- Department of Internal Medicine-Gerontology, Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Zhong-Min Wang
- Department of Internal Medicine-Gerontology, Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Claudia Hereñú
- Biochemistry Research Institute of La Plata (INIBIOLP)/National Scientific and Technical Research Council (CONICET), School of Medicine, National University of La Plata, 1900 La Plata, BA, Argentina
| | - Pei-Fen Kuan
- Department of Applied Mathematics and Statistics, Stony Brook University, Stony Brook, NY 11794
| | - Osvaldo Delbono
- Department of Internal Medicine-Gerontology, Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC 27157Department of Internal Medicine-Gerontology, Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC 27157
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7
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Rebbeck RT, Karunasekara Y, Board PG, Beard NA, Casarotto MG, Dulhunty AF. Skeletal muscle excitation–contraction coupling: Who are the dancing partners? Int J Biochem Cell Biol 2014; 48:28-38. [DOI: 10.1016/j.biocel.2013.12.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2013] [Revised: 11/29/2013] [Accepted: 12/04/2013] [Indexed: 01/15/2023]
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Horstick EJ, Gibbs EM, Li X, Davidson AE, Dowling JJ. Analysis of embryonic and larval zebrafish skeletal myofibers from dissociated preparations. J Vis Exp 2013:e50259. [PMID: 24300240 DOI: 10.3791/50259] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
The zebrafish has proven to be a valuable model system for exploring skeletal muscle function and for studying human muscle diseases. Despite the many advantages offered by in vivo analysis of skeletal muscle in the zebrafish, visualizing the complex and finely structured protein milieu responsible for muscle function, especially in whole embryos, can be problematic. This hindrance stems from the small size of zebrafish skeletal muscle (60 μm) and the even smaller size of the sarcomere. Here we describe and demonstrate a simple and rapid method for isolating skeletal myofibers from zebrafish embryos and larvae. We also include protocols that illustrate post preparation techniques useful for analyzing muscle structure and function. Specifically, we detail the subsequent immunocytochemical localization of skeletal muscle proteins and the qualitative analysis of stimulated calcium release via live cell calcium imaging. Overall, this video article provides a straight-forward and efficient method for the isolation and characterization of zebrafish skeletal myofibers, a technique which provides a conduit for myriad subsequent studies of muscle structure and function.
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Affiliation(s)
- Eric J Horstick
- Departments of Pediatrics and Neurology, University of Michigan
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9
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Amador FJ, Stathopulos PB, Enomoto M, Ikura M. Ryanodine receptor calcium release channels: lessons from structure-function studies. FEBS J 2013; 280:5456-70. [PMID: 23413940 DOI: 10.1111/febs.12194] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Revised: 01/24/2013] [Accepted: 02/04/2013] [Indexed: 11/28/2022]
Abstract
Ryanodine receptors (RyRs) are the largest known ion channels. They are Ca(2+) release channels found primarily on the sarcoplasmic reticulum of myocytes. Several hundred mutations in RyRs are associated with skeletal or cardiomyocyte disease in humans. Many of these mutations can now be mapped onto the high resolution structures of individual RyR domains and on full-length tetrameric cryo-electron microscopy structures. A closely related Ca(2+) release channel, the inositol 1,4,5-trisphospate receptor (IP3 R), shows a conserved structural architecture at the N-terminus, suggesting that both channels evolved from an ancestral unicellular RyR/IP3 R. The functional insights provided by recent structural studies for both channels will aid in the development of rationale treatments for a myriad of Ca(2+)-signaled malignancies.
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Affiliation(s)
- Fernando J Amador
- Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, Canada
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10
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Polster A, Ohrtman JD, Beam KG, Papadopoulos S. Fluorescence resonance energy transfer (FRET) indicates that association with the type I ryanodine receptor (RyR1) causes reorientation of multiple cytoplasmic domains of the dihydropyridine receptor (DHPR) α(1S) subunit. J Biol Chem 2012; 287:41560-8. [PMID: 23071115 DOI: 10.1074/jbc.m112.404194] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The skeletal muscle dihydropyridine receptor (DHPR) in the t-tubular membrane serves as the Ca(2+) channel and voltage sensor for excitation-contraction (EC) coupling, triggering Ca(2+) release via the type 1 ryanodine receptor (RyR1) in the sarcoplasmic reticulum (SR). The two proteins appear to be physically linked, and both the α(1S) and β(1a) subunits of the DHPR are essential for EC coupling. Within α(1S), cytoplasmic domains of importance include the I-II loop (to which β(1a) binds), the II-III and III-IV loops, and the C terminus. However, the spatial relationship of these domains to one another has not been established. Here, we have taken the approach of measuring FRET between fluorescent proteins inserted into pairs of α(1S) cytoplasmic domains. Expression of these constructs in dyspedic (RyR1 null) and dysgenic (α(1S) null) myotubes was used to test for function and targeting to plasma membrane/SR junctions and to test whether the presence of RyR1 caused altered FRET. We found that in the absence of RyR1, measureable FRET occurred between the N terminus and C terminus (residue 1636), and between the II-III loop (residue 626) and both the N and C termini; the I-II loop (residue 406) showed weak FRET with the II-III loop but not with the N terminus. Association with RyR1 caused II-III loop FRET to decrease with the C terminus and increase with the N terminus and caused I-II loop FRET to increase with both the II-III loop and N terminus. Overall, RyR1 appears to cause a substantial reorientation of the cytoplasmic α(1S) domains consistent with their becoming more closely packed.
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Affiliation(s)
- Alexander Polster
- Department of Vegetative Physiology, University of Cologne, D-50931 Cologne, Germany
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11
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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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12
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Sheridan DC, Moua O, Lorenzon NM, Beam KG. Bimolecular fluorescence complementation and targeted biotinylation provide insight into the topology of the skeletal muscle Ca ( 2+) channel β1a subunit. Channels (Austin) 2012; 6:26-40. [PMID: 22522946 DOI: 10.4161/chan.18916] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
In skeletal muscle, L-type calcium channels (DHPRs), localized to plasma membrane sarcoplasmic reticulum junctions, are tightly packed into groups of four termed tetrads. Here, we have used bimolecular fluorescence complementation (BiFC) and targeted biotinylation to probe the structure and organization of β1a subunits associated with native CaV 1.1 in DHPRs of myotubes. The construct YN-β1a-YC, in which the non-fluorescent fragments of YFP ("YN" corresponding to YFP residues 1-158, and "YC" corresponding to YFP residues 159-238) were fused, respectively, to the N- and C-termini of β1a, was fully functional and displayed yellow fluorescence within DHPR tetrads after expression in β1-knockout (β1KO) myotubes; this yellow fluorescence demonstrated the occurrence of BiFC of YN and YC on the β1a N- and C-termini. In these experiments, we avoided overexpression because control experiments in non-muscle cells indicated that this could result in non-specific BiFC. BiFC of YN-β1a-YC in DHPR tetrads appeared to be intramolecular between N- and C-termini of individual β1a subunits rather than between adjacent DHPRs because BiFC (1) was observed for YN-β1a-YC co-expressed with CaV 1.2 (which does not form tetrads) and (2) was not observed after co-expression of YN-β1a-YN plus YC-β1a-YC in β1KO myotubes. Thus, β1a function is compatible with N- and C-termini being close enough together to allow BiFC. However, both termini appeared to have positional freedom and not to be closely opposed by other junctional proteins since both were accessible to gold-streptavidin conjugates. Based on these results, a model is proposed for the arrangement of β1a subunits in DHPR tetrads.
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Affiliation(s)
- David C Sheridan
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
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13
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Huang CLH, Pedersen TH, Fraser JA. Reciprocal dihydropyridine and ryanodine receptor interactions in skeletal muscle activation. J Muscle Res Cell Motil 2011; 32:171-202. [PMID: 21993921 DOI: 10.1007/s10974-011-9262-9] [Citation(s) in RCA: 110] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2011] [Accepted: 09/12/2011] [Indexed: 11/25/2022]
Abstract
Dihydropyridine (DHPR) and ryanodine receptors (RyRs) are central to transduction of transverse (T) tubular membrane depolarisation initiated by surface action potentials into release of sarcoplasmic reticular (SR) Ca2+ in skeletal muscle excitation-contraction coupling. Electronmicroscopic methods demonstrate an orderly positioning of such tubular DHPRs relative to RyRs in the SR at triad junctions where their membranes come into close proximity. Biochemical and genetic studies associated expression of specific, DHPR and RyR, isoforms with the particular excitation-contraction coupling processes and related elementary Ca2+ release events found respectively in skeletal and cardiac muscle. Physiological studies of intramembrane charge movements potentially related to voltage triggering of Ca2+ release demonstrated a particular qγ charging species identifiable with DHPRs through its T-tubular localization, pharmacological properties, and steep voltage-dependence paralleling Ca2+ release. Its nonlinear kinetics implicated highly co-operative conformational events in its transitions in response to voltage change. The effects of DHPR and RyR agonists and antagonists upon this intramembrane charge in turn implicated reciprocal rather than merely unidirectional DHPR-RyR interactions in these complex reactions. Thus, following membrane potential depolarization, an orthograde qγ-DHPR-RyR signaling likely initiates conformational alterations in the RyR with which it makes contact. The latter changes could then retrogradely promote further qγ-DHPR transitions through reciprocal co-operative allosteric interactions between receptors. These would relieve the resting constraints on both further, delayed, nonlinear qγ-DHPR charge transfers and on RyR-mediated Ca2+ release. They would also explain the more rapid charging and recovery qγ transients following larger depolarizations and membrane potential repolarization to the resting level.
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Affiliation(s)
- Christopher L-H Huang
- Physiological Laboratory, Department of Biochemistry, University of Cambridge, Cambridge, CB2 3EG, UK.
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14
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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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15
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Karunasekara Y, Dulhunty AF, Casarotto MG. The voltage-gated calcium-channel beta subunit: more than just an accessory. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:75-81. [PMID: 19455319 DOI: 10.1007/s00249-009-0467-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2009] [Revised: 04/22/2009] [Accepted: 04/29/2009] [Indexed: 11/25/2022]
Abstract
Voltage-gated Ca(2+) channels (VGCCs) are involved in a number of excitatory processes in the cell that regulate muscle contraction, neurotransmitter release, gene regulation, and neuronal migration. They consist of a central pore-forming alpha(1) subunit together with a number of associated auxiliary subunits including a cytoplasmic beta subunit. With the aid of X-ray crystallography, it has been found that the beta subunits of VGCCs (beta(2a), beta(3), and beta(4)) interact strongly with the I-II loop of the pore-forming alpha(1) subunit. Here we discuss the potential interaction sites of beta(1a) with its alpha(1) subunit as well as the skeletal ryanodine receptor. We suggest that not only can beta(1a) interact with the alpha(1) subunit I-II loop, but more subtle interactions may be possible through the II-III loop via the beta(1a) SH3 domain. Such findings could have important implications with respect to EC coupling.
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Affiliation(s)
- Yamuna Karunasekara
- The John Curtin School of Medical Research, Australian National University, GPO Box 334, Canberra, ACT, 2601, Australia
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16
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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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Bedoukian MA, Weeks AM, Partin KM. Different Domains of the AMPA Receptor Direct Stargazin-mediated Trafficking and Stargazin-mediated Modulation of Kinetics. J Biol Chem 2006; 281:23908-21. [PMID: 16793768 DOI: 10.1074/jbc.m600679200] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Stargazin is an accessory protein of AMPA receptors that enhances surface expression and also affects the biophysical properties of the receptor. AMPA receptor domains necessary for either of these two processes have not yet been identified. Here, we used confocal imaging and electrophysiology of heterologously expressed, fluorophore-tagged GluR1, GluR2, and stargazin to study surface expression and desensitization kinetics. Stargazin-mediated trafficking was sensitive to the nature of the AMPA receptor cytoplasmic domain. The insertion of YFP after residue 15 of the truncated cytoplasmic tail of GluR1i perturbed stargazin-mediated trafficking of the receptor but not its modulation of desensitization kinetics. This construct also failed to permit fluorescence resonance energy transfer (FRET) with stargazin in the endoplasmic reticulum (ER), whereas FRET between fluorophore-tagged stargazin and non-truncated AMPA receptors demonstrated a specific interaction between these proteins, both in the ER and the plasma membrane. Rather than encoding a specific binding site, the fluorophore-tagged C terminus may restrict access to one or more ER retention sites. Although perturbations of the C terminus impeded stargazin-mediated trafficking to the plasma membrane, the effects of stargazin on the biophysical properties of AMPA receptors (i.e. modulation of desensitization) remained intact. These data provide strong evidence that the AMPA receptor domains required for stargazin modulation of gating and trafficking are separable.
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Affiliation(s)
- Matthew A Bedoukian
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado 80523, USA
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