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Maverick EE, Tamkun MM. High spatial density is associated with non-conducting Kv channels from two families. Biophys J 2022; 121:755-768. [PMID: 35101417 PMCID: PMC8943702 DOI: 10.1016/j.bpj.2022.01.021] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Revised: 12/14/2021] [Accepted: 01/25/2022] [Indexed: 11/02/2022] Open
Abstract
Ion channels are well known for their ability to regulate the cell membrane potential. However, many ion channels also have functions that do not involve ion conductance. Kv2 channels are one family of ion channels whose non-conducting functions are central to mammalian cell physiology. Kv2.1 and Kv2.2 channels form stable contact sites between the endoplasmic reticulum and plasma membrane via an interaction with endoplasmic reticulum resident proteins. To perform this structural role, Kv2 channels are expressed at extremely high densities on the plasma membranes of many cell types, including central pyramidal neurons, α-motoneurons, and smooth muscle cells. Research from our lab and others has shown that the majority of these plasma membrane Kv2.1 channels do not conduct potassium in response to depolarization. The mechanism of this channel silencing is unknown but is thought to be dependent on channel density in the membrane. Furthermore, the prevalence of a non-conducting population of Kv2.2 channels has not been directly tested. In this work we make improved measurements of the numbers of conducting and non-conducting Kv2.1 channels expressed in HEK293 cells and expand the investigation of non-conducting channels to three additional Kv α-subunits: Kv2.2, Kv1.4, and Kv1.5. By comparing the numbers of gating and conducting channels in individual HEK293 cells, we found that on average, only 50% of both Kv2.1 and Kv2.2 channels conducted potassium and, as previously suggested, that fraction decreased with increased channel density in the plasma membrane. At the highest spatial densities tested, which are comparable with those found at Kv2 clusters in situ, only 20% of Kv2.1 and Kv2.2 channels conducted potassium. We also show for the first time that Kv1.4 and Kv1.5 exhibit density-dependent silencing, suggesting that this phenomenon has an underlying mechanism that is shared by Kv channels from multiple families.
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Affiliation(s)
- Emily E. Maverick
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado,Molecular, Cellular and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado
| | - Michael M. Tamkun
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado,Molecular, Cellular and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado,Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado,Corresponding author
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2
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Kravenska Y, Checchetto V, Szabo I. Routes for Potassium Ions across Mitochondrial Membranes: A Biophysical Point of View with Special Focus on the ATP-Sensitive K + Channel. Biomolecules 2021; 11:1172. [PMID: 34439838 PMCID: PMC8393992 DOI: 10.3390/biom11081172] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 07/29/2021] [Accepted: 08/02/2021] [Indexed: 12/18/2022] Open
Abstract
Potassium ions can cross both the outer and inner mitochondrial membranes by means of multiple routes. A few potassium-permeable ion channels exist in the outer membrane, while in the inner membrane, a multitude of different potassium-selective and potassium-permeable channels mediate K+ uptake into energized mitochondria. In contrast, potassium is exported from the matrix thanks to an H+/K+ exchanger whose molecular identity is still debated. Among the K+ channels of the inner mitochondrial membrane, the most widely studied is the ATP-dependent potassium channel, whose pharmacological activation protects cells against ischemic damage and neuronal injury. In this review, we briefly summarize and compare the different hypotheses regarding the molecular identity of this patho-physiologically relevant channel, taking into account the electrophysiological characteristics of the proposed components. In addition, we discuss the characteristics of the other channels sharing localization to both the plasma membrane and mitochondria.
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Affiliation(s)
| | | | - Ildiko Szabo
- Department of Biology, University of Padova, 35131 Padova, Italy; (Y.K.); (V.C.)
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Scheiper-Welling S, Zuccolini P, Rauh O, Beckmann BM, Geisen C, Moroni A, Thiel G, Kauferstein S. Characterization of an N-terminal Na v1.5 channel variant - a potential risk factor for arrhythmias and sudden death? BMC MEDICAL GENETICS 2020; 21:227. [PMID: 33213388 PMCID: PMC7678220 DOI: 10.1186/s12881-020-01170-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Accepted: 11/10/2020] [Indexed: 12/19/2022]
Abstract
Background Alterations in the SCN5A gene encoding the cardiac sodium channel Nav1.5 have been linked to a number of arrhythmia syndromes and diseases including long-QT syndrome (LQTS), Brugada syndrome (BrS) and dilative cardiomyopathy (DCM), which may predispose to fatal arrhythmias and sudden death. We identified the heterozygous variant c.316A > G, p.(Ser106Gly) in a 35-year-old patient with survived cardiac arrest. In the present study, we aimed to investigate the functional impact of the variant to clarify the medical relevance. Methods Mutant as well as wild type GFP tagged Nav1.5 channels were expressed in HEK293 cells. We performed functional characterization experiments using patch-clamp technique. Results Electrophysiological measurements indicated, that the detected missense variant alters Nav1.5 channel functionality leading to a gain-of-function effect. Cells expressing S106G channels show an increase in Nav1.5 current over the entire voltage window. Conclusion The results support the assumption that the detected sequence aberration alters Nav1.5 channel function and may predispose to cardiac arrhythmias and sudden cardiac death. Supplementary Information The online version contains supplementary material available at 10.1186/s12881-020-01170-3.
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Affiliation(s)
- Stefanie Scheiper-Welling
- Institute of Legal Medicine, Goethe University of Frankfurt, Kennedyallee 104, 60596, Frankfurt am Main, Germany
| | - Paolo Zuccolini
- Department of Biology, Membrane Biophysics, Technische Universität Darmstadt, Schnittspahnstrasse 3, 64287, Darmstadt, Germany
| | - Oliver Rauh
- Department of Biology, Membrane Biophysics, Technische Universität Darmstadt, Schnittspahnstrasse 3, 64287, Darmstadt, Germany
| | - Britt-Maria Beckmann
- 1 Institute of Legal Medicine, Goethe University of Frankfurt, Kennedyallee104, 60596, Frankfurt am Main, Germany
| | - Christof Geisen
- German Red Cross Blood Center, Institute of Transfusion Medicine and Immunohaematology, University Hospital Frankfurt, Frankfurt, Germany
| | - Anna Moroni
- Department of Biosciences and CNR IBF-Mi, University of Milano, Via Celoria 26, 20133, Milan, Italy
| | - Gerhard Thiel
- Department of Biology, Membrane Biophysics, Technische Universität Darmstadt, Schnittspahnstrasse 3, 64287, Darmstadt, Germany
| | - Silke Kauferstein
- Institute of Legal Medicine, Goethe University of Frankfurt, Kennedyallee 104, 60596, Frankfurt am Main, Germany.
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Zhu M, Idikuda VK, Wang J, Wei F, Kumar V, Shah N, Waite CB, Liu Q, Zhou L. Shank3-deficient thalamocortical neurons show HCN channelopathy and alterations in intrinsic electrical properties. J Physiol 2018; 596:1259-1276. [PMID: 29327340 DOI: 10.1113/jp275147] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2017] [Accepted: 01/04/2018] [Indexed: 01/11/2023] Open
Abstract
KEY POINTS Shank3 increases the HCN channel surface expression in heterologous expression systems. Shank3Δ13-16 deficiency causes significant reduction in HCN2 expression and Ih current amplitude in thalamocortical (TC) neurons. Shank3Δ13-16 - but not Shank3Δ4-9 -deficient TC neurons share changes in basic electrical properties which are comparable to those of HCN2-/- TC neurons. HCN channelopathy may critically mediate events downstream from Shank3 deficiency. ABSTRACT SHANK3 is a scaffolding protein that is highly enriched in excitatory synapses. Mutations in the SHANK3 gene have been linked to neuropsychiatric disorders especially the autism spectrum disorders. SHANK3 deficiency is known to cause impairments in synaptic transmission, but its effects on basic neuronal electrical properties that are more localized to the soma and proximal dendrites remain unclear. Here we confirmed that in heterologous expression systems two different mouse Shank3 isoforms, Shank3A and Shank3C, significantly increase the surface expression of the mouse hyperpolarization-activated, cyclic-nucleotide-gated (HCN) channel. In Shank3Δ13-16 knockout mice, which lack exons 13-16 in the Shank3 gene (both Shank3A and Shank3C are removed) and display a severe behavioural phenotype, the expression of HCN2 is reduced to an undetectable level. The thalamocortical (TC) neurons from the ventrobasal (VB) complex of Shank3Δ13-16 mice demonstrate reduced Ih current amplitude and correspondingly increased input resistance, negatively shifted resting membrane potential, and abnormal spike firing in both tonic and burst modes. Impressively, these changes closely resemble those of HCN2-/- TC neurons but not of the TC neurons from Shank3Δ4-9 mice, which lack exons 4-9 in the Shank3 gene (Shank3C still exists) and demonstrate moderate behavioural phenotypes. Additionally, Shank3 deficiency increases the ratio of excitatory/inhibitory balance in VB neurons but has a limited impact on the electrical properties of connected thalamic reticular (RTN) neurons. These results provide new understanding about the role of HCN channelopathy in mediating detrimental effects downstream from Shank3 deficiency.
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Affiliation(s)
- Mengye Zhu
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA.,Department of Pain Clinic, The First Affiliated Hospital of Nanchang University, Nanchang, Jiangxi, China
| | - Vinay Kumar Idikuda
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA
| | - Jianbing Wang
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA.,Department of Anesthesiology, Jiangxi Cancer Hospital, Nanchang, Jiangxi, China
| | - Fusheng Wei
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA.,Department of Anesthesiology, The First Affiliated Hospital of Nanchang University, Nanchang, Jiangxi, China
| | - Virang Kumar
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA
| | - Nikhil Shah
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA
| | - Christopher B Waite
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA
| | - Qinglian Liu
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA
| | - Lei Zhou
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, USA
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Sartiani L, Mannaioni G, Masi A, Novella Romanelli M, Cerbai E. The Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels: from Biophysics to Pharmacology of a Unique Family of Ion Channels. Pharmacol Rev 2017; 69:354-395. [PMID: 28878030 DOI: 10.1124/pr.117.014035] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Accepted: 07/07/2017] [Indexed: 12/22/2022] Open
Abstract
Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels are important members of the voltage-gated pore loop channels family. They show unique features: they open at hyperpolarizing potential, carry a mixed Na/K current, and are regulated by cyclic nucleotides. Four different isoforms have been cloned (HCN1-4) that can assemble to form homo- or heterotetramers, characterized by different biophysical properties. These proteins are widely distributed throughout the body and involved in different physiologic processes, the most important being the generation of spontaneous electrical activity in the heart and the regulation of synaptic transmission in the brain. Their role in heart rate, neuronal pacemaking, dendritic integration, learning and memory, and visual and pain perceptions has been extensively studied; these channels have been found also in some peripheral tissues, where their functions still need to be fully elucidated. Genetic defects and altered expression of HCN channels are linked to several pathologies, which makes these proteins attractive targets for translational research; at the moment only one drug (ivabradine), which specifically blocks the hyperpolarization-activated current, is clinically available. This review discusses current knowledge about HCN channels, starting from their biophysical properties, origin, and developmental features, to (patho)physiologic role in different tissues and pharmacological modulation, ending with their present and future relevance as drug targets.
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Affiliation(s)
- Laura Sartiani
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Guido Mannaioni
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Alessio Masi
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Maria Novella Romanelli
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Elisabetta Cerbai
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
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Saponaro A, Porro A, Chaves-Sanjuan A, Nardini M, Rauh O, Thiel G, Moroni A. Fusicoccin Activates KAT1 Channels by Stabilizing Their Interaction with 14-3-3 Proteins. THE PLANT CELL 2017; 29:2570-2580. [PMID: 28970335 PMCID: PMC5774578 DOI: 10.1105/tpc.17.00375] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Revised: 08/31/2017] [Accepted: 09/27/2017] [Indexed: 05/20/2023]
Abstract
Plants acquire potassium (K+) ions for cell growth and movement via regulated diffusion through K+ channels. Here, we present crystallographic and functional data showing that the K+ inward rectifier KAT1 (K+Arabidopsis thaliana 1) channel is regulated by 14-3-3 proteins and further modulated by the phytotoxin fusicoccin, in analogy to the H+-ATPase. We identified a 14-3-3 mode III binding site at the very C terminus of KAT1 and cocrystallized it with tobacco (Nicotiana tabacum) 14-3-3 proteins to describe the protein complex at atomic detail. Validation of this interaction by electrophysiology shows that 14-3-3 binding augments KAT1 conductance by increasing the maximal current and by positively shifting the voltage dependency of gating. Fusicoccin potentiates the 14-3-3 effect on KAT1 activity by stabilizing their interaction. Crystal structure of the ternary complex reveals a noncanonical binding site for the toxin that adopts a novel conformation. The structural insights underscore the adaptability of fusicoccin, predicting more potential targets than so far anticipated. The data further advocate a common mechanism of regulation of the proton pump and a potassium channel, two essential elements in K+ uptake in plant cells.
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Affiliation(s)
- Andrea Saponaro
- Department of Biosciences, University of Milan, 20133 Milan, Italy
| | - Alessandro Porro
- Department of Biosciences, University of Milan, 20133 Milan, Italy
| | | | - Marco Nardini
- Department of Biosciences, University of Milan, 20133 Milan, Italy
| | - Oliver Rauh
- Plant Membrane Biophysics, Technical University Darmstadt, 64287 Darmstadt, Germany
| | - Gerhard Thiel
- Plant Membrane Biophysics, Technical University Darmstadt, 64287 Darmstadt, Germany
| | - Anna Moroni
- Department of Biosciences, University of Milan, 20133 Milan, Italy
- Institute for Biophysics-Milan, Consiglio Nazionale delle Ricerche, 20133 Milan, Italy
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