Pub Date : 2020-12-01DOI: 10.1080/19336950.2020.1829842
Felix Neumaier, Toni Schneider, Walid Albanna
Voltage-gated calcium channels (VGCCs) are critical for Ca2+ influx into all types of excitable cells, but their exact function is still poorly understood. Recent reconstruction of homology models for all human VGCCs at atomic resolution provides the opportunity for a structure-based discussion of VGCC function and novel insights into the mechanisms underlying Ca2+ selective flux through these channels. In the present review, we use these data as a basis to examine the structure, function, and Zn2+-induced modulation of Cav2.3 VGCCs, which mediate native R-type currents and belong to the most enigmatic members of the family. Their unique sensitivity to Zn2+ and the existence of multiple mechanisms of Zn2+ action strongly argue for a role of these channels in the modulatory action of endogenous loosely bound Zn2+, pools of which have been detected in a number of neuronal, endocrine, and reproductive tissues. Following a description of the different mechanisms by which Zn2+ has been shown or is thought to alter the function of these channels, we discuss their potential (patho)physiological relevance, taking into account what is known about the magnitude and function of extracellular Zn2+ signals in different tissues. While still far from complete, the picture that emerges is one where Cav2.3 channel expression parallels the occurrence of loosely bound Zn2+ pools in different tissues and where these channels may serve to translate physiological Zn2+ signals into changes of electrical activity and/or intracellular Ca2+ levels.
{"title":"Ca<sub>v</sub>2.3 channel function and Zn<sup>2+</sup>-induced modulation: potential mechanisms and (patho)physiological relevance.","authors":"Felix Neumaier, Toni Schneider, Walid Albanna","doi":"10.1080/19336950.2020.1829842","DOIUrl":"https://doi.org/10.1080/19336950.2020.1829842","url":null,"abstract":"<p><p>Voltage-gated calcium channels (VGCCs) are critical for Ca<sup>2+</sup> influx into all types of excitable cells, but their exact function is still poorly understood. Recent reconstruction of homology models for all human VGCCs at atomic resolution provides the opportunity for a structure-based discussion of VGCC function and novel insights into the mechanisms underlying Ca<sup>2+</sup> selective flux through these channels. In the present review, we use these data as a basis to examine the structure, function, and Zn<sup>2+</sup>-induced modulation of Ca<sub>v</sub>2.3 VGCCs, which mediate native R-type currents and belong to the most enigmatic members of the family. Their unique sensitivity to Zn<sup>2+</sup> and the existence of multiple mechanisms of Zn<sup>2+</sup> action strongly argue for a role of these channels in the modulatory action of endogenous loosely bound Zn<sup>2+</sup>, pools of which have been detected in a number of neuronal, endocrine, and reproductive tissues. Following a description of the different mechanisms by which Zn<sup>2+</sup> has been shown or is thought to alter the function of these channels, we discuss their potential (patho)physiological relevance, taking into account what is known about the magnitude and function of extracellular Zn<sup>2+</sup> signals in different tissues. While still far from complete, the picture that emerges is one where Ca<sub>v</sub>2.3 channel expression parallels the occurrence of loosely bound Zn<sup>2+</sup> pools in different tissues and where these channels may serve to translate physiological Zn<sup>2+</sup> signals into changes of electrical activity and/or intracellular Ca<sup>2+</sup> levels.</p>","PeriodicalId":72555,"journal":{"name":"Channels (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19336950.2020.1829842","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38509085","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-01DOI: 10.1080/19336950.2020.1740501
Ye Han, Kyle A Lyman, Kendall M Foote, Dane M Chetkovich
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed throughout the mammalian central nervous system (CNS). These channels have been implicated in a wide range of diseases, including Major Depressive Disorder and multiple subtypes of epilepsy. The diversity of functions that HCN channels perform is in part attributable to differences in their subcellular localization. To facilitate a broad range of subcellular distributions, HCN channels are bound by auxiliary subunits that regulate surface trafficking and channel function. One of the best studied auxiliary subunits is tetratricopeptide-repeat containing, Rab8b-interacting protein (TRIP8b). TRIP8b is an extensively alternatively spliced protein whose only known function is to regulate HCN channels. TRIP8b binds to HCN pore-forming subunits at multiple interaction sites that differentially regulate HCN channel function and subcellular distribution. In this review, we summarize what is currently known about the structure and function of TRIP8b isoforms with an emphasis on the role of this auxiliary subunit in health and disease.
{"title":"The structure and function of TRIP8b, an auxiliary subunit of hyperpolarization-activated cyclic-nucleotide gated channels.","authors":"Ye Han, Kyle A Lyman, Kendall M Foote, Dane M Chetkovich","doi":"10.1080/19336950.2020.1740501","DOIUrl":"10.1080/19336950.2020.1740501","url":null,"abstract":"<p><p>Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed throughout the mammalian central nervous system (CNS). These channels have been implicated in a wide range of diseases, including Major Depressive Disorder and multiple subtypes of epilepsy. The diversity of functions that HCN channels perform is in part attributable to differences in their subcellular localization. To facilitate a broad range of subcellular distributions, HCN channels are bound by auxiliary subunits that regulate surface trafficking and channel function. One of the best studied auxiliary subunits is tetratricopeptide-repeat containing, Rab8b-interacting protein (TRIP8b). TRIP8b is an extensively alternatively spliced protein whose only known function is to regulate HCN channels. TRIP8b binds to HCN pore-forming subunits at multiple interaction sites that differentially regulate HCN channel function and subcellular distribution. In this review, we summarize what is currently known about the structure and function of TRIP8b isoforms with an emphasis on the role of this auxiliary subunit in health and disease.</p>","PeriodicalId":72555,"journal":{"name":"Channels (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ftp.ncbi.nlm.nih.gov/pub/pmc/oa_pdf/85/6a/kchl-14-01-1740501.PMC7153792.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"37751938","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/19336950.2019.1600968
Gary J Stephens, Graeme S Cottrell
Autocommentary to: Cottrell GS, Soubrane CH, Hounshell JA, Lin H, Owenson V, Rigby M, Cox PJ, Barker BS, Ottolini M, Ince S, Bauer, CC, Perez-Reyes E, Patel MK, Stevens EB, Stephens GJ (2018) CACHD1 is an 2-like protein that modulates CaV3 voltage-gated calcium channel activity J Neurosci 38:9186-9201.
{"title":"CACHD1: A new activity-modifying protein for voltage-gated calcium channels.","authors":"Gary J Stephens, Graeme S Cottrell","doi":"10.1080/19336950.2019.1600968","DOIUrl":"https://doi.org/10.1080/19336950.2019.1600968","url":null,"abstract":"Autocommentary to: Cottrell GS, Soubrane CH, Hounshell JA, Lin H, Owenson V, Rigby M, Cox PJ, Barker BS, Ottolini M, Ince S, Bauer, CC, Perez-Reyes E, Patel MK, Stevens EB, Stephens GJ (2018) CACHD1 is an 2-like protein that modulates CaV3 voltage-gated calcium channel activity J Neurosci 38:9186-9201.","PeriodicalId":72555,"journal":{"name":"Channels (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19336950.2019.1600968","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"37151098","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/19336950.2019.1568825
Yousra El Ghaleb, Marta Campiglio, Bernhard E Flucher
The voltage-gated calcium channel CaV1.1a primarily functions as voltage-sensor in skeletal muscle excitation-contraction (EC) coupling. In embryonic muscle the splice variant CaV1.1e, which lacks exon 29, additionally function as a genuine L-type calcium channel. Because previous work in most laboratories used a CaV1.1 expression plasmid containing a single amino acid substitution (R165K) of a critical gating charge in the first voltage-sensing domain (VSD), we corrected this substitution and analyzed its effects on the gating properties of the L-type calcium currents in dysgenic myotubes. Reverting K165 to R right-shifted the voltage-dependence of activation by ~12 mV in both CaV1.1 splice variants without changing their current amplitudes or kinetics. This demonstrates the exquisite sensitivity of the voltage-sensor function to changes in the specific amino acid side chains independent of their charge. Our results further indicate the cooperativity of VSDs I and IV in determining the voltage-sensitivity of CaV1.1 channel gating.
电压门控钙通道 CaV1.1a 在骨骼肌兴奋-收缩(EC)耦合过程中主要起电压传感器的作用。在胚胎肌肉中,缺少第 29 号外显子的剪接变体 CaV1.1e 还具有真正的 L 型钙通道功能。由于大多数实验室之前的工作使用的 CaV1.1 表达质粒含有第一个电压感应结构域(VSD)中一个关键门控电荷的单个氨基酸置换(R165K),我们对该置换进行了校正,并分析了其对发育不良肌管中 L 型钙离子电流门控特性的影响。在两种 CaV1.1 拼接变体中,将 K165 改为 R 可使激活的电压依赖性右移约 12 mV,而不会改变它们的电流幅度或动力学。这表明电压传感器功能对特定氨基酸侧链的变化非常敏感,与其电荷无关。我们的研究结果进一步表明,VSD I 和 IV 在决定 CaV1.1 通道门控的电压敏感性方面具有协同作用。
{"title":"Correcting the R165K substitution in the first voltage-sensor of Ca<sub>V</sub>1.1 right-shifts the voltage-dependence of skeletal muscle calcium channel activation.","authors":"Yousra El Ghaleb, Marta Campiglio, Bernhard E Flucher","doi":"10.1080/19336950.2019.1568825","DOIUrl":"10.1080/19336950.2019.1568825","url":null,"abstract":"<p><p>The voltage-gated calcium channel Ca<sub>V</sub>1.1a primarily functions as voltage-sensor in skeletal muscle excitation-contraction (EC) coupling. In embryonic muscle the splice variant Ca<sub>V</sub>1.1e, which lacks exon 29, additionally function as a genuine L-type calcium channel. Because previous work in most laboratories used a Ca<sub>V</sub>1.1 expression plasmid containing a single amino acid substitution (R165K) of a critical gating charge in the first voltage-sensing domain (VSD), we corrected this substitution and analyzed its effects on the gating properties of the L-type calcium currents in dysgenic myotubes. Reverting K165 to R right-shifted the voltage-dependence of activation by ~12 mV in both Ca<sub>V</sub>1.1 splice variants without changing their current amplitudes or kinetics. This demonstrates the exquisite sensitivity of the voltage-sensor function to changes in the specific amino acid side chains independent of their charge. Our results further indicate the cooperativity of VSDs I and IV in determining the voltage-sensitivity of Ca<sub>V</sub>1.1 channel gating.</p>","PeriodicalId":72555,"journal":{"name":"Channels (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6380215/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"36849085","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/19336950.2019.1635864
Edward Glasscock
Voltage-gated Kv1.1 potassium channel α-subunits are broadly expressed in the nervous system where they act as critical regulators of neuronal excitability. Mutations in the KCNA1 gene, which encodes Kv1.1, are associated with the neurological diseases episodic ataxia and epilepsy. Studies in mouse models have shown that Kv1.1 is important for neural control of the heart and that Kcna1 deletion leads to cardiac dysfunction that appears to be brain-driven. Traditionally, KCNA1 was not believed to be expressed in the heart. However, recent studies have revealed that Kv1.1 subunits are not only present in cardiomyocytes, but that they also make an important heart-intrinsic functional contribution to outward K+ currents and action potential repolarization. This review recounts the winding history of discovery of KCNA1 gene expression and neurocardiac function from fruit flies to mammals and from brain to heart and looks at some of the salient questions that remain to be answered regarding emerging cardiac roles of Kv1.1.
{"title":"Kv1.1 channel subunits in the control of neurocardiac function.","authors":"Edward Glasscock","doi":"10.1080/19336950.2019.1635864","DOIUrl":"https://doi.org/10.1080/19336950.2019.1635864","url":null,"abstract":"<p><p>Voltage-gated Kv1.1 potassium channel α-subunits are broadly expressed in the nervous system where they act as critical regulators of neuronal excitability. Mutations in the <i>KCNA1</i> gene, which encodes Kv1.1, are associated with the neurological diseases episodic ataxia and epilepsy. Studies in mouse models have shown that Kv1.1 is important for neural control of the heart and that <i>Kcna1</i> deletion leads to cardiac dysfunction that appears to be brain-driven. Traditionally, <i>KCNA1</i> was not believed to be expressed in the heart. However, recent studies have revealed that Kv1.1 subunits are not only present in cardiomyocytes, but that they also make an important heart-intrinsic functional contribution to outward K<sup>+</sup> currents and action potential repolarization. This review recounts the winding history of discovery of <i>KCNA1</i> gene expression and neurocardiac function from fruit flies to mammals and from brain to heart and looks at some of the salient questions that remain to be answered regarding emerging cardiac roles of Kv1.1.</p>","PeriodicalId":72555,"journal":{"name":"Channels (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19336950.2019.1635864","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"37098172","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/19336950.2019.1626793
Ana Elena López-Romero, Ileana Hernández-Araiza, Francisco Torres-Quiroz, Luis B Tovar-Y-Romo, León D Islas, Tamara Rosenbaum
Ion channels display conformational changes in response to binding of their agonists and antagonists. The study of the relationships between the structure and the function of these proteins has witnessed considerable advances in the last two decades using a combination of techniques, which include electrophysiology, optical approaches (i.e. patch clamp fluorometry, incorporation of non-canonic amino acids, etc.), molecular biology (mutations in different regions of ion channels to determine their role in function) and those that have permitted the resolution of their structures in detail (X-ray crystallography and cryo-electron microscopy). The possibility of making correlations among structural components and functional traits in ion channels has allowed for more refined conclusions on how these proteins work at the molecular level. With the cloning and description of the family of Transient Receptor Potential (TRP) channels, our understanding of several sensory-related processes has also greatly moved forward. The response of these proteins to several agonists, their regulation by signaling pathways as well as by protein-protein and lipid-protein interactions and, in some cases, their biophysical characteristics have been studied thoroughly and, recently, with the resolution of their structures, the field has experienced a new boom. This review article focuses on the conformational changes in the pores, concentrating on some members of the TRP family of ion channels (TRPV and TRPA subfamilies) that result in changes in their single-channel conductances, a phenomenon that may lead to fine-tuning the electrical response to a given agonist in a cell.
{"title":"TRP ion channels: Proteins with conformational flexibility.","authors":"Ana Elena López-Romero, Ileana Hernández-Araiza, Francisco Torres-Quiroz, Luis B Tovar-Y-Romo, León D Islas, Tamara Rosenbaum","doi":"10.1080/19336950.2019.1626793","DOIUrl":"https://doi.org/10.1080/19336950.2019.1626793","url":null,"abstract":"<p><p>Ion channels display conformational changes in response to binding of their agonists and antagonists. The study of the relationships between the structure and the function of these proteins has witnessed considerable advances in the last two decades using a combination of techniques, which include electrophysiology, optical approaches (i.e. patch clamp fluorometry, incorporation of non-canonic amino acids, etc.), molecular biology (mutations in different regions of ion channels to determine their role in function) and those that have permitted the resolution of their structures in detail (X-ray crystallography and cryo-electron microscopy). The possibility of making correlations among structural components and functional traits in ion channels has allowed for more refined conclusions on how these proteins work at the molecular level. With the cloning and description of the family of Transient Receptor Potential (TRP) channels, our understanding of several sensory-related processes has also greatly moved forward. The response of these proteins to several agonists, their regulation by signaling pathways as well as by protein-protein and lipid-protein interactions and, in some cases, their biophysical characteristics have been studied thoroughly and, recently, with the resolution of their structures, the field has experienced a new boom. This review article focuses on the conformational changes in the pores, concentrating on some members of the TRP family of ion channels (TRPV and TRPA subfamilies) that result in changes in their single-channel conductances, a phenomenon that may lead to fine-tuning the electrical response to a given agonist in a cell.</p>","PeriodicalId":72555,"journal":{"name":"Channels (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19336950.2019.1626793","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"37319007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/19336950.2018.1557470
Anna Boccaccio, Eleonora Di Zanni, Antonella Gradogna, Joachim Scholz-Starke
The TMEM16E protein (synonymous to anocta min 5) has been attracting a great deal of interest, since mutations in the human TMEM16E gene were implicated in two different types of hereditary diseases: in gnathodiaphyseal dysplasia (GDD), a rare skeletal syndrome [1], and in muscular dystrophies, limb-girdle muscular dystrophy-2L (LGMD2L) and distal Miyoshi myopathy (MMD3) [2]. Yet for many years, it was not even known which may be the very basic function carried out by this membrane protein, let alone how this function may contribute to physiological and pathophysiological settings. Several facets have contributed to this uncertainty surrounding TMEM16E function. While proteins of the TMEM16 family were initially considered Ca-activated chloride channels, it became clear later that many of them are in reality Ca-activated lipid scramblases mediating the stimulus-induced passive transport of phospholipids, in particular phosphatidylserine (PtdSer), between the leaflets of the membrane bilayer (for review [3]). Moreover, early localization studies indicated that native or heterologously expressed TMEM16E protein was restricted to intracellular membranes and therefore inaccessible to classical approaches like whole-cell patchclamp and scrambling assays [4]. This uncertainty has now been dispelled. Several studies published in recent years concur on the fact that TMEM16E belongs to the group of family members with Ca-activated phospholipid scrambling (PLS) activity. A first hint in favour of the “scramblase” option came from a chimeric approach in which a 35-aa-long stretch connecting trans-membrane domains 4 and 5 (designated “scrambling domain” in the TMEM16F sister protein [5]) was swapped between TMEM16E and the plasma membrane-localized TMEM16A. Introduction of the short TMEM16E stretch was sufficient to endow the Ca-activated chloride channel TMEM16A with lipid scrambling activity [6]. Work from our group provided direct demonstration of Ca dependent PLS for the human TMEM16E wild-type protein exploiting its partial plasma membrane (PM) localization following transient overexpression in HEK293 cells [7]. Targeting of a TMEM16E-EGFP fusion to the cell surface was shown by colocalization with the PM marker FM4-64. Additional independent evidence for partial PM localization came from surface biotinylation assays on HEK293 cells stably overexpressing a codon-optimized hTMEM16E version [8]. It is not yet clear if the PM localization of TMEM16E has relevance in its diverse physiological contexts or if it is simply a consequence of protein overexpression. Data from isolated mouse muscle cells indicate that TMEM16E PLS activity may indeed contribute to extracellular PtdSer exposure [8] (see below). Detection of PLS typically relies on annexin-V binding to PtdSer accumulating in the outer leaflet of the membrane as a consequence of scrambling activity. In both HEK293 cell models [7,8], scrambling assays concurrently revealed annexin-V binding at the cell
{"title":"Lifting the veils on TMEM16E function.","authors":"Anna Boccaccio, Eleonora Di Zanni, Antonella Gradogna, Joachim Scholz-Starke","doi":"10.1080/19336950.2018.1557470","DOIUrl":"https://doi.org/10.1080/19336950.2018.1557470","url":null,"abstract":"The TMEM16E protein (synonymous to anocta min 5) has been attracting a great deal of interest, since mutations in the human TMEM16E gene were implicated in two different types of hereditary diseases: in gnathodiaphyseal dysplasia (GDD), a rare skeletal syndrome [1], and in muscular dystrophies, limb-girdle muscular dystrophy-2L (LGMD2L) and distal Miyoshi myopathy (MMD3) [2]. Yet for many years, it was not even known which may be the very basic function carried out by this membrane protein, let alone how this function may contribute to physiological and pathophysiological settings. Several facets have contributed to this uncertainty surrounding TMEM16E function. While proteins of the TMEM16 family were initially considered Ca-activated chloride channels, it became clear later that many of them are in reality Ca-activated lipid scramblases mediating the stimulus-induced passive transport of phospholipids, in particular phosphatidylserine (PtdSer), between the leaflets of the membrane bilayer (for review [3]). Moreover, early localization studies indicated that native or heterologously expressed TMEM16E protein was restricted to intracellular membranes and therefore inaccessible to classical approaches like whole-cell patchclamp and scrambling assays [4]. This uncertainty has now been dispelled. Several studies published in recent years concur on the fact that TMEM16E belongs to the group of family members with Ca-activated phospholipid scrambling (PLS) activity. A first hint in favour of the “scramblase” option came from a chimeric approach in which a 35-aa-long stretch connecting trans-membrane domains 4 and 5 (designated “scrambling domain” in the TMEM16F sister protein [5]) was swapped between TMEM16E and the plasma membrane-localized TMEM16A. Introduction of the short TMEM16E stretch was sufficient to endow the Ca-activated chloride channel TMEM16A with lipid scrambling activity [6]. Work from our group provided direct demonstration of Ca dependent PLS for the human TMEM16E wild-type protein exploiting its partial plasma membrane (PM) localization following transient overexpression in HEK293 cells [7]. Targeting of a TMEM16E-EGFP fusion to the cell surface was shown by colocalization with the PM marker FM4-64. Additional independent evidence for partial PM localization came from surface biotinylation assays on HEK293 cells stably overexpressing a codon-optimized hTMEM16E version [8]. It is not yet clear if the PM localization of TMEM16E has relevance in its diverse physiological contexts or if it is simply a consequence of protein overexpression. Data from isolated mouse muscle cells indicate that TMEM16E PLS activity may indeed contribute to extracellular PtdSer exposure [8] (see below). Detection of PLS typically relies on annexin-V binding to PtdSer accumulating in the outer leaflet of the membrane as a consequence of scrambling activity. In both HEK293 cell models [7,8], scrambling assays concurrently revealed annexin-V binding at the cell","PeriodicalId":72555,"journal":{"name":"Channels (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19336950.2018.1557470","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"36888875","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/19336950.2019.1600967
Shan Huang, Wei Zhang, Xueli Chang, Junhong Guo
Objective: To verify the diagnosis of channelopathies in two families and explore the mechanism of the overlap between periodic paralysis (PP) and paramyotonia congenita (PMC).
Methods: We have studied two cases with overlapping symptoms of episodic weakness and stiffness in our clinical center using a series of assessment including detailed medical history, careful physical examination, laboratory analyses, muscle biopsy, electrophysiological evaluation, and genetic analysis.
Results: The first proband and part of his family with the overlap of PMC and hyperkalemic periodic paralysis (HyperPP) has been identified as c.2111C > T (T704M) substitution of the gene SCN4A. The second proband and part of his family with the overlap of PMC and hypokalemic periodic paralysis type 2 (HypoPP2) has been identified as c.4343G > A (R1448H) substitution of the gene SCN4A. In addition, one member of the second family with overlapping symptoms has been identified as a novel mutation c.2111C > T without the mutation c.4343G > A.
Conclusions: SCN4A gene mutations can cause the overlap of PMC and PP (especially the HypoPP2). The clinical symptoms of episodic weakness and stiffness could happen at a different time or temperature. Based on diagnosis assessments such as medical history and muscle biopsy, further evaluations on long-time exercise test, genetic analysis, and patch clamp electrophysiology test need to be done in order to verify the specific subtype of channelopathies. Furthermore, the improvement of one member in the pregnancy period can be used as a reference for the other female in the child-bearing period with T704M.
目的:验证两家系对经络病的诊断,探讨周期性麻痹(PP)与先天性肌张力旁缩症(PMC)重叠的发病机制。方法:我们通过详细的病史、仔细的体格检查、实验室分析、肌肉活检、电生理评估和基因分析等一系列评估方法,研究了两例发作性无力和僵硬症状重叠的病例。结果:PMC和高钾血症性周期性麻痹(HyperPP)重叠的第一先证者及其部分家族被鉴定为c.2111C > T (T704M) SCN4A基因替代。第二先证及其部分家族成员与PMC和低钾性周期性麻痹2型(HypoPP2)重叠,已被确定为c.4343G > A (R1448H) SCN4A基因替代。此外,第二家族中有一名具有重叠症状的成员被鉴定为一种新的突变c.2111C > T,而没有突变c.4343G > a。结论:SCN4A基因突变可导致PMC和PP重叠(尤其是HypoPP2)。发作性虚弱和僵硬的临床症状可能发生在不同的时间或温度。在病史和肌肉活检等诊断评估的基础上,需要进一步通过长期运动试验、基因分析和膜片钳电生理试验进行评估,以验证通道病变的具体亚型。此外,妊娠期一名成员的改善可以作为生育期另一名女性T704M的参考。
{"title":"Overlap of periodic paralysis and paramyotonia congenita caused by SCN4A gene mutations two family reports and literature review.","authors":"Shan Huang, Wei Zhang, Xueli Chang, Junhong Guo","doi":"10.1080/19336950.2019.1600967","DOIUrl":"https://doi.org/10.1080/19336950.2019.1600967","url":null,"abstract":"<p><strong>Objective: </strong>To verify the diagnosis of channelopathies in two families and explore the mechanism of the overlap between periodic paralysis (PP) and paramyotonia congenita (PMC).</p><p><strong>Methods: </strong>We have studied two cases with overlapping symptoms of episodic weakness and stiffness in our clinical center using a series of assessment including detailed medical history, careful physical examination, laboratory analyses, muscle biopsy, electrophysiological evaluation, and genetic analysis.</p><p><strong>Results: </strong>The first proband and part of his family with the overlap of PMC and hyperkalemic periodic paralysis (HyperPP) has been identified as c.2111C > T (T704M) substitution of the gene SCN4A. The second proband and part of his family with the overlap of PMC and hypokalemic periodic paralysis type 2 (HypoPP2) has been identified as c.4343G > A (R1448H) substitution of the gene SCN4A. In addition, one member of the second family with overlapping symptoms has been identified as a novel mutation c.2111C > T without the mutation c.4343G > A.</p><p><strong>Conclusions: </strong>SCN4A gene mutations can cause the overlap of PMC and PP (especially the HypoPP2). The clinical symptoms of episodic weakness and stiffness could happen at a different time or temperature. Based on diagnosis assessments such as medical history and muscle biopsy, further evaluations on long-time exercise test, genetic analysis, and patch clamp electrophysiology test need to be done in order to verify the specific subtype of channelopathies. Furthermore, the improvement of one member in the pregnancy period can be used as a reference for the other female in the child-bearing period with T704M.</p>","PeriodicalId":72555,"journal":{"name":"Channels (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/19336950.2019.1600967","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"37269796","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/19336950.2019.1632670
Peter R Strege, Arnaldo Mercado-Perez, Amelia Mazzone, Yuri A Saito, Cheryl E Bernard, Gianrico Farrugia, Arthur Beyder
SCN5A is expressed in cardiomyocytes and gastrointestinal (GI) smooth muscle cells (SMCs) as the voltage-gated mechanosensitive sodium channel NaV1.5. The influx of Na+ through NaV1.5 produces a fast depolarization in membrane potential, indispensable for electrical excitability in cardiomyocytes and important for electrical slow waves in GI smooth muscle. As such, abnormal NaV1.5 voltage gating or mechanosensitivity may result in channelopathies. SCN5A mutation G615E - found separately in cases of acquired long-QT syndrome, sudden cardiac death, and irritable bowel syndrome - has a relatively minor effect on NaV1.5 voltage gating. The aim of this study was to test whether G615E impacts mechanosensitivity. Mechanosensitivity of wild-type (WT) or G615E-NaV1.5 in HEK-293 cells was examined by shear stress on voltage- or current-clamped whole cells or pressure on macroscopic patches. Unlike WT, voltage-clamped G615E-NaV1.5 showed a loss in shear- and pressure-sensitivity of peak current yet a normal leftward shift in the voltage-dependence of activation. In current-clamp, shear stress led to a significant increase in firing spike frequency with a decrease in firing threshold for WT but not G615E-NaV1.5. Our results show that the G615E mutation leads to functionally abnormal NaV1.5 channels, which cause disruptions in mechanosensitivity and mechano-electrical feedback and suggest a potential contribution to smooth muscle pathophysiology.
{"title":"<i>SCN5A</i> mutation G615E results in Na<sub>V</sub>1.5 voltage-gated sodium channels with normal voltage-dependent function yet loss of mechanosensitivity.","authors":"Peter R Strege, Arnaldo Mercado-Perez, Amelia Mazzone, Yuri A Saito, Cheryl E Bernard, Gianrico Farrugia, Arthur Beyder","doi":"10.1080/19336950.2019.1632670","DOIUrl":"10.1080/19336950.2019.1632670","url":null,"abstract":"<p><p><i>SCN5A</i> is expressed in cardiomyocytes and gastrointestinal (GI) smooth muscle cells (SMCs) as the voltage-gated mechanosensitive sodium channel Na<sub>V</sub>1.5. The influx of Na<sup>+</sup> through Na<sub>V</sub>1.5 produces a fast depolarization in membrane potential, indispensable for electrical excitability in cardiomyocytes and important for electrical slow waves in GI smooth muscle. As such, abnormal Na<sub>V</sub>1.5 voltage gating or mechanosensitivity may result in channelopathies. <i>SCN5A</i> mutation G615E - found separately in cases of acquired long-QT syndrome, sudden cardiac death, and irritable bowel syndrome - has a relatively minor effect on Na<sub>V</sub>1.5 voltage gating. The aim of this study was to test whether G615E impacts mechanosensitivity. Mechanosensitivity of wild-type (WT) or G615E-Na<sub>V</sub>1.5 in HEK-293 cells was examined by shear stress on voltage- or current-clamped whole cells or pressure on macroscopic patches. Unlike WT, voltage-clamped G615E-Na<sub>V</sub>1.5 showed a loss in shear- and pressure-sensitivity of peak current yet a normal leftward shift in the voltage-dependence of activation. In current-clamp, shear stress led to a significant increase in firing spike frequency with a decrease in firing threshold for WT but not G615E-Na<sub>V</sub>1.5. Our results show that the G615E mutation leads to functionally abnormal Na<sub>V</sub>1.5 channels, which cause disruptions in mechanosensitivity and mechano-electrical feedback and suggest a potential contribution to smooth muscle pathophysiology.</p>","PeriodicalId":72555,"journal":{"name":"Channels (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6629189/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"37386585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/19336950.2019.1586046
Oskar B Jaggers, Pietro Ridone, Boris Martinac, Matthew A B Baker
Mechanosensitive ion channels are membrane gated pores which are activated by mechanical stimuli. The focus of this study is on Piezo1, a newly discovered, large, mammalian, mechanosensitive ion channel, which has been linked to diseases such as dehydrated hereditary stomatocytosis (Xerocytosis) and lymphatic dysplasia. Here we utilize an established in-vitro artificial bilayer system to interrogate single Piezo1 channel activity. The droplet-hydrogel bilayer (DHB) system uniquely allows the simultaneous recording of electrical activity and fluorescence imaging of labelled protein. We successfully reconstituted fluorescently labelled Piezo1 ion channels in DHBs and verified activity using electrophysiology in the same system. We demonstrate successful insertion and activation of hPiezo1-GFP in bilayers of varying composition. Furthermore, we compare the Piezo1 bilayer reconstitution with measurements of insertion and activation of KcsA channels to reproduce the channel conductances reported in the literature. Together, our results showcase the use of DHBs for future experiments allowing simultaneous measurements of ion channel gating while visualising the channel proteins using fluorescence.
{"title":"Fluorescence microscopy of piezo1 in droplet hydrogel bilayers.","authors":"Oskar B Jaggers, Pietro Ridone, Boris Martinac, Matthew A B Baker","doi":"10.1080/19336950.2019.1586046","DOIUrl":"10.1080/19336950.2019.1586046","url":null,"abstract":"<p><p>Mechanosensitive ion channels are membrane gated pores which are activated by mechanical stimuli. The focus of this study is on Piezo1, a newly discovered, large, mammalian, mechanosensitive ion channel, which has been linked to diseases such as dehydrated hereditary stomatocytosis (Xerocytosis) and lymphatic dysplasia. Here we utilize an established in-vitro artificial bilayer system to interrogate single Piezo1 channel activity. The droplet-hydrogel bilayer (DHB) system uniquely allows the simultaneous recording of electrical activity and fluorescence imaging of labelled protein. We successfully reconstituted fluorescently labelled Piezo1 ion channels in DHBs and verified activity using electrophysiology in the same system. We demonstrate successful insertion and activation of hPiezo1-GFP in bilayers of varying composition. Furthermore, we compare the Piezo1 bilayer reconstitution with measurements of insertion and activation of KcsA channels to reproduce the channel conductances reported in the literature. Together, our results showcase the use of DHBs for future experiments allowing simultaneous measurements of ion channel gating while visualising the channel proteins using fluorescence.</p>","PeriodicalId":72555,"journal":{"name":"Channels (Austin, Tex.)","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6527062/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"37229597","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}