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Stewart RG, Marquis MJ, Jo S, Aberra A, Cook V, Whiddon Z, Ferns M, Sack JT. A Kv2 inhibitor combination reveals native neuronal conductances consistent with Kv2/KvS heteromers. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.31.578214. [PMID: 38352561 PMCID: PMC10862871 DOI: 10.1101/2024.01.31.578214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2024]
Abstract
KvS proteins are voltage-gated potassium channel subunits that form functional channels when assembled into heterotetramers with Kv2.1 ( KCNB1 ) or Kv2.2 ( KCNB2 ). Mammals have 10 KvS subunits: Kv5.1 ( KCNF1 ), Kv6.1 ( KCNG1 ), Kv6.2 ( KCNG2 ), Kv6.3 ( KCNG3 ), Kv6.4 ( KCNG4 ), Kv8.1 ( KCNV1 ), Kv8.2 ( KCNV2 ), Kv9.1 ( KCNS1 ), Kv9.2 ( KCNS2 ), and Kv9.3 ( KCNS3 ). Electrically excitable cells broadly express channels containing Kv2 subunits and most neurons have substantial Kv2 conductance. However, whether KvS subunits contribute to these conductances has not been clear, leaving the physiological roles of KvS subunits poorly understood. Here, we identify that two potent Kv2 inhibitors, used in combination, can distinguish conductances of Kv2/KvS channels and Kv2-only channels. We find that Kv5, Kv6, Kv8, or Kv9-containing channels are resistant to the Kv2-selective pore-blocker RY785 yet remain sensitive to the Kv2-selective voltage sensor modulator guangxitoxin-1E (GxTX). Using these inhibitors in mouse superior cervical ganglion neurons, we find that little of the Kv2 conductance is carried by KvS-containing channels. In contrast, conductances consistent with KvS-containing channels predominate over Kv2-only channels in mouse and human dorsal root ganglion neurons. These results establish an approach to pharmacologically distinguish conductances of Kv2/KvS heteromers from Kv2-only channels, enabling investigation of the physiological roles of endogenous KvS subunits. These findings suggest that drugs targeting KvS subunits could modulate electrical activity of subsets of Kv2-expressing cell types.
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2
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Simonson BT, Jegla M, Ryan JF, Jegla T. Functional analysis of ctenophore Shaker K + channels: N-type inactivation in the animal roots. Biophys J 2024:S0006-3495(24)00068-7. [PMID: 38291751 DOI: 10.1016/j.bpj.2024.01.027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 11/16/2023] [Accepted: 01/24/2024] [Indexed: 02/01/2024] Open
Abstract
Here we explore the evolutionary origins of fast N-type ball-and-chain inactivation in Shaker (Kv1) K+ channels by functionally characterizing Shaker channels from the ctenophore (comb jelly) Mnemiopsis leidyi. Ctenophores are the sister lineage to other animals and Mnemiopsis has >40 Shaker-like K+ channels, but they have not been functionally characterized. We identified three Mnemiopsis channels (MlShak3-5) with N-type inactivation ball-like sequences at their N termini and functionally expressed them in Xenopus oocytes. Two of the channels, MlShak4 and MlShak5, showed rapid inactivation similar to cnidarian and bilaterian Shakers with rapid N-type inactivation, whereas MlShak3 inactivated ∼100-fold more slowly. Fast inactivation in MlShak4 and MlShak5 required the putative N-terminal inactivation ball sequences. Furthermore, the rate of fast inactivation in these channels depended on the number of inactivation balls/channel, but the rate of recovery from inactivation did not. These findings closely match the mechanism of N-type inactivation first described for Drosophila Shaker in which 1) inactivation balls on the N termini of each subunit can independently block the pore, and 2) only one inactivation ball occupies the pore binding site at a time. These findings suggest classical N-type activation evolved in Shaker channels at the very base of the animal phylogeny in a common ancestor of ctenophores, cnidarians, and bilaterians and that fast-inactivating Shakers are therefore a fundamental type of animal K+ channel. Interestingly, we find evidence from functional co-expression experiments and molecular dynamics that MlShak4 and MlShak5 do not co-assemble, suggesting that Mnemiopsis has at least two functionally independent N-type Shaker channels.
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Affiliation(s)
- Benjamin T Simonson
- Department of Biology and Huck Institutes of the Life Sciences, Penn State University, University Park, Pennsylvania
| | - Max Jegla
- Department of Biology and Huck Institutes of the Life Sciences, Penn State University, University Park, Pennsylvania
| | - Joseph F Ryan
- Whitney Laboratory for Marine Bioscience, University of Florida, St. Augustine, FL; Department of Biology, University of Florida, Gainesville, FL
| | - Timothy Jegla
- Department of Biology and Huck Institutes of the Life Sciences, Penn State University, University Park, Pennsylvania.
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3
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Ferns M, van der List D, Vierra NC, Lacey T, Murray K, Kirmiz M, Stewart RG, Sack JT, Trimmer JS. Electrically silent KvS subunits associate with native Kv2 channels in brain and impact diverse properties of channel function. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.25.577135. [PMID: 38328147 PMCID: PMC10849721 DOI: 10.1101/2024.01.25.577135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2024]
Abstract
Voltage-gated K+ channels of the Kv2 family are highly expressed in brain and play dual roles in regulating neuronal excitability and in organizing endoplasmic reticulum - plasma membrane (ER-PM) junctions. Studies in heterologous cells suggest that the two pore-forming alpha subunits Kv2.1 and Kv2.2 assemble with "electrically silent" KvS subunits to form heterotetrameric channels with distinct biophysical properties. Here, using mass spectrometry-based proteomics, we identified five KvS subunits as components of native Kv2.1 channels immunopurified from mouse brain, the most abundant being Kv5.1. We found that Kv5.1 co-immunoprecipitates with Kv2.1 and to a lesser extent with Kv2.2 from brain lysates, and that Kv5.1 protein levels are decreased by 70% in Kv2.1 knockout mice and 95% in Kv2.1/2.2 double knockout mice. Multiplex immunofluorescent labelling of rodent brain sections revealed that in neocortex Kv5.1 immunolabeling is apparent in a large percentage of Kv2.1 and Kv2.2-positive layer 2/3 neurons, and in a smaller percentage of layer 5 and 6 neurons. At the subcellular level, Kv5.1 is co-clustered with Kv2.1 and Kv2.2 at ER-PM junctions in cortical neurons, although clustering of Kv5.1-containing channels is reduced relative to homomeric Kv2 channels. We also found that in heterologous cells coexpression with Kv5.1 reduces the clustering and alters the pharmacological properties of Kv2.1 channels. Together, these findings demonstrate that the Kv5.1 electrically silent subunit is a component of a substantial fraction of native brain Kv2 channels, and that its incorporation into heteromeric channels can impact diverse aspects of Kv2 channel function.
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Affiliation(s)
- Michael Ferns
- Dept. of Anesthesiology and Pain Medicine, University of California Davis, One Shields Ave, Davis, CA 95616, USA
- Dept. of Physiology and Membrane Biology, University of California Davis, One Shields Ave, Davis, CA 95616, USA
| | - Deborah van der List
- Dept. of Physiology and Membrane Biology, University of California Davis, One Shields Ave, Davis, CA 95616, USA
| | - Nicholas C. Vierra
- Dept. of Physiology and Membrane Biology, University of California Davis, One Shields Ave, Davis, CA 95616, USA
| | - Taylor Lacey
- Dept. of Anesthesiology and Pain Medicine, University of California Davis, One Shields Ave, Davis, CA 95616, USA
| | - Karl Murray
- Dept. of Physiology and Membrane Biology, University of California Davis, One Shields Ave, Davis, CA 95616, USA
- Dept. of Psychiatry and Behavioral Sciences, University of California Davis, One Shields Ave, Davis, CA 95616, USA
| | - Michael Kirmiz
- Dept. of Physiology and Membrane Biology, University of California Davis, One Shields Ave, Davis, CA 95616, USA
| | - Robert G. Stewart
- Dept. of Physiology and Membrane Biology, University of California Davis, One Shields Ave, Davis, CA 95616, USA
| | - Jon T. Sack
- Dept. of Physiology and Membrane Biology, University of California Davis, One Shields Ave, Davis, CA 95616, USA
| | - James S. Trimmer
- Dept. of Physiology and Membrane Biology, University of California Davis, One Shields Ave, Davis, CA 95616, USA
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4
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Ramirez-Navarro A, Lima-Silveira L, Glazebrook PA, Dantzler HA, Kline DD, Kunze DL. Kv2 channels contribute to neuronal activity within the vagal afferent-nTS reflex arc. Am J Physiol Cell Physiol 2024; 326:C74-C88. [PMID: 37982174 DOI: 10.1152/ajpcell.00366.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Revised: 11/07/2023] [Accepted: 11/14/2023] [Indexed: 11/21/2023]
Abstract
Diversity in the functional expression of ion channels contributes to the unique patterns of activity generated in visceral sensory A-type myelinated neurons versus C-type unmyelinated neurons in response to their natural stimuli. In the present study, Kv2 channels were identified as underlying a previously uncharacterized delayed rectifying potassium current expressed in both A- and C-type nodose ganglion neurons. Kv2.1 and 2.2 appear confined to the soma and initial segment of these sensory neurons; however, neither was identified in their central presynaptic terminals projecting onto relay neurons in the nucleus of the solitary tract (nTS). Kv2.1 and Kv2.2 were also not detected in the peripheral axons and sensory terminals in the aortic arch. Functionally, in nodose neuron somas, Kv2 currents exhibited frequency-dependent current inactivation and contributed to action potential repolarization in C-type neurons but not A-type neurons. Within the nTS, the block of Kv2 currents does not influence afferent presynaptic calcium influx or glutamate release in response to afferent activation, supporting our immunohistochemical observations. On the other hand, Kv2 channels contribute to membrane hyperpolarization and limit action potential discharge rate in second-order neurons. Together, these data demonstrate that Kv2 channels influence neuronal discharge within the vagal afferent-nTS circuit and indicate they may play a significant role in viscerosensory reflex function.NEW & NOTEWORTHY We demonstrate the expression and function of the voltage-gated delayed rectifier potassium channel Kv2 in vagal nodose neurons. Within sensory neurons, Kv2 channels limit the width of the broader C-type but not narrow A-type action potential. Within the nucleus of the solitary tract (nTS), the location of the vagal terminal field, Kv2 does not influence glutamate release. However, Kv2 limits the action potential discharge of nTS relay neurons. These data suggest a critical role for Kv2 in the vagal-nTS reflex arc.
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Affiliation(s)
- Angelina Ramirez-Navarro
- Rammelkamp Center for Education and Research, MetroHealth Medical Center Campus, Case Western Reserve University, Cleveland, Ohio, United States
- Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio, United States
| | - Ludmila Lima-Silveira
- Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri, United States
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States
| | - Patricia A Glazebrook
- Rammelkamp Center for Education and Research, MetroHealth Medical Center Campus, Case Western Reserve University, Cleveland, Ohio, United States
- Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio, United States
| | - Heather A Dantzler
- Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri, United States
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States
| | - David D Kline
- Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri, United States
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States
| | - Diana L Kunze
- Rammelkamp Center for Education and Research, MetroHealth Medical Center Campus, Case Western Reserve University, Cleveland, Ohio, United States
- Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio, United States
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5
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Zhao W, Zhang Q, Su Y, Chen X, Li X, Du B, Deng X, Ji F, Li J, Dong Q, Chen C, Li J. Effect of schizophrenia risk gene polymorphisms on cognitive and neural plasticity. Schizophr Res 2022; 248:173-179. [PMID: 36075127 DOI: 10.1016/j.schres.2022.08.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2021] [Revised: 07/13/2022] [Accepted: 08/20/2022] [Indexed: 11/24/2022]
Abstract
A recent Chinese genome-wide association study found evidence for 58 out of the 128 schizophrenia-associated variants previously discovered in Western samples by the Schizophrenia Working Group of the Psychiatric Genomics Consortium (PGC). However, the functional impact of these trans-ancestry genome-wide single-nucleotide polymorphisms (SNPs) is not clear. In the current study, we examined the roles of trans-ancestry SNPs in cognitive and neural plasticity. We first performed a behavioral study of 547 healthy volunteers, who received month-long working memory training, and working memory capability assessment both before and after the training. A separate sample of 101 subjects received the same training and received fMRI scans during a working memory task, both before and after the training. The behavioral study found a significant association between the polygenic risk score (PRS) and behavioral plasticity, with higher schizophrenia risk scores being linked to less plasticity. At the SNP level, rs36068923 showed a significant signal, with the risk allele being associated with less plasticity. The fMRI study further found that the PRS and rs36068923 polymorphism were associated with training-induced changes in striatal activation, with higher PRS and the risk allele of rs36068923 being linked to less brain plasticity. In sum, this study found that a high genetic risk for schizophrenia was associated with less plasticity at both behavioral and neural levels. These results provide new insights into the neural and cognitive mechanisms linking genes to schizophrenia.
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Affiliation(s)
- Wan Zhao
- School of Psychology, Nanjing Normal University, Nanjing 210097, Jiangsu, PR China
| | - Qiumei Zhang
- State Key Laboratory of Cognitive Neuroscience and Learning & IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing 100875, PR China; School of Public Health, Jining Medical University, Jining 272013, Shandong, PR China
| | - Yanyan Su
- State Key Laboratory of Cognitive Neuroscience and Learning & IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing 100875, PR China
| | - Xiongying Chen
- The National Clinical Research Center for Mental Disorders & Beijing Key Laboratory of Mental Disorders & the Advanced Innovation Center for Human Brain Protection, Beijing Anding Hospital, School of Mental Health, Capital Medical University, Beijing 100088, PR China
| | - Xiaohong Li
- The National Clinical Research Center for Mental Disorders & Beijing Key Laboratory of Mental Disorders & the Advanced Innovation Center for Human Brain Protection, Beijing Anding Hospital, School of Mental Health, Capital Medical University, Beijing 100088, PR China
| | - Boqi Du
- State Key Laboratory of Cognitive Neuroscience and Learning & IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing 100875, PR China
| | - Xiaoxiang Deng
- State Key Laboratory of Cognitive Neuroscience and Learning & IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing 100875, PR China
| | - Feng Ji
- School of Mental Health, Jining Medical University, Jining 272013, Shandong, PR China
| | - Jin Li
- Brainnetome Center, Institute of Automation, Chinese Academy of Sciences, 95 East Zhongguancun Road, Beijing 100190, PR China; National Laboratory of Pattern Recognition, Institute of Automation, Chinese Academy of Sciences, 95 East Zhongguancun Road, Beijing 100190, PR China
| | - Qi Dong
- State Key Laboratory of Cognitive Neuroscience and Learning & IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing 100875, PR China
| | - Chuansheng Chen
- Department of Psychological Science, University of California, Irvine, CA 92697, United States
| | - Jun Li
- State Key Laboratory of Cognitive Neuroscience and Learning & IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing 100875, PR China.
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6
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Boscia F, Elkjaer ML, Illes Z, Kukley M. Altered Expression of Ion Channels in White Matter Lesions of Progressive Multiple Sclerosis: What Do We Know About Their Function? Front Cell Neurosci 2021; 15:685703. [PMID: 34276310 PMCID: PMC8282214 DOI: 10.3389/fncel.2021.685703] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Accepted: 05/23/2021] [Indexed: 12/19/2022] Open
Abstract
Despite significant advances in our understanding of the pathophysiology of multiple sclerosis (MS), knowledge about contribution of individual ion channels to axonal impairment and remyelination failure in progressive MS remains incomplete. Ion channel families play a fundamental role in maintaining white matter (WM) integrity and in regulating WM activities in axons, interstitial neurons, glia, and vascular cells. Recently, transcriptomic studies have considerably increased insight into the gene expression changes that occur in diverse WM lesions and the gene expression fingerprint of specific WM cells associated with secondary progressive MS. Here, we review the ion channel genes encoding K+, Ca2+, Na+, and Cl- channels; ryanodine receptors; TRP channels; and others that are significantly and uniquely dysregulated in active, chronic active, inactive, remyelinating WM lesions, and normal-appearing WM of secondary progressive MS brain, based on recently published bulk and single-nuclei RNA-sequencing datasets. We discuss the current state of knowledge about the corresponding ion channels and their implication in the MS brain or in experimental models of MS. This comprehensive review suggests that the intense upregulation of voltage-gated Na+ channel genes in WM lesions with ongoing tissue damage may reflect the imbalance of Na+ homeostasis that is observed in progressive MS brain, while the upregulation of a large number of voltage-gated K+ channel genes may be linked to a protective response to limit neuronal excitability. In addition, the altered chloride homeostasis, revealed by the significant downregulation of voltage-gated Cl- channels in MS lesions, may contribute to an altered inhibitory neurotransmission and increased excitability.
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Affiliation(s)
- Francesca Boscia
- Division of Pharmacology, Department of Neuroscience, Reproductive and Dentistry Sciences, School of Medicine, University of Naples "Federico II", Naples, Italy
| | - Maria Louise Elkjaer
- Neurology Research Unit, Department of Clinical Research, University of Southern Denmark, Odense, Denmark.,Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Zsolt Illes
- Neurology Research Unit, Department of Clinical Research, University of Southern Denmark, Odense, Denmark.,Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark.,Department of Neurology, Odense University Hospital, Odense, Denmark
| | - Maria Kukley
- Achucarro Basque Center for Neuroscience, Leioa, Spain.,Ikerbasque Basque Foundation for Science, Bilbao, Spain
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7
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Khoubza L, Chatelain FC, Feliciangeli S, Lesage F, Bichet D. Physiological roles of heteromerization: focus on the two-pore domain potassium channels. J Physiol 2021; 599:1041-1055. [PMID: 33347640 DOI: 10.1113/jp279870] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Accepted: 12/07/2020] [Indexed: 12/28/2022] Open
Abstract
Potassium channels form the largest family of ion channels with more than 80 members involved in cell excitability and signalling. Most of them exist as homomeric channels, whereas specific conditions are required to obtain heteromeric channels. It is well established that heteromerization of voltage-gated and inward rectifier potassium channels affects their function, increasing the diversity of the native potassium currents. For potassium channels with two pore domains (K2P ), homomerization has long been considered the rule, their polymodal regulation by a wide diversity of physical and chemical stimuli being responsible for the adaptation of the leak potassium currents to cellular needs. This view has recently evolved with the accumulation of evidence of heteromerization between different K2P subunits. Several functional intragroup and intergroup heteromers have recently been identified, which contribute to the functional heterogeneity of this family. K2P heteromerization is involved in the modulation of channel expression and trafficking, promoting functional and signalling diversity. As illustrated in the Abstract Figure, heteromerization of TREK1 and TRAAK provides the cell with more possibilities of regulation. It is becoming increasingly evident that K2P heteromers contribute to important physiological functions including neuronal and cardiac excitability. Since heteromerization also affects the pharmacology of K2P channels, this understanding helps to establish K2P heteromers as new therapeutic targets for physiopathological conditions.
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Affiliation(s)
- Lamyaa Khoubza
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, 660 route des Lucioles 06650 Valbonne, France
| | - Franck C Chatelain
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, 660 route des Lucioles 06650 Valbonne, France
| | - Sylvain Feliciangeli
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, 660 route des Lucioles 06650 Valbonne, France.,Inserm, 101 rue de Tolbiac, 75013, Paris, France
| | - Florian Lesage
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, 660 route des Lucioles 06650 Valbonne, France.,Inserm, 101 rue de Tolbiac, 75013, Paris, France
| | - Delphine Bichet
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, 660 route des Lucioles 06650 Valbonne, France
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8
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Fenyves BG, Arnold A, Gharat VG, Haab C, Tishinov K, Peter F, de Quervain D, Papassotiropoulos A, Stetak A. Dual Role of an mps-2/KCNE-Dependent Pathway in Long-Term Memory and Age-Dependent Memory Decline. Curr Biol 2020; 31:527-539.e7. [PMID: 33259792 DOI: 10.1016/j.cub.2020.10.069] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 09/14/2020] [Accepted: 10/21/2020] [Indexed: 01/24/2023]
Abstract
Activity-dependent persistent changes in neuronal intrinsic excitability and synaptic strength are underlying learning and memory. Voltage-gated potassium (Kv) channels are potential regulators of memory and may be linked to age-dependent neuronal disfunction. MinK-related peptides (MiRPs) are conserved transmembrane proteins modulating Kv channels; however, their possible role in the regulation of memory and age-dependent memory decline are unknown. Here, we show that, in C. elegans, mps-2 is the sole member of the MiRP family that controls exclusively long-term associative memory (LTAM) in AVA neuron. In addition, we demonstrate that mps-2 also plays a critical role in age-dependent memory decline. In young adult worms, mps-2 is transcriptionally upregulated by CRH-1/cyclic AMP (cAMP)-response-binding protein (CREB) during LTAM, although the mps-2 baseline expression is CREB independent and instead, during aging, relies on nhr-66, which acts as an age-dependent repressor. Deletion of nhr-66 or its binding element in the mps-2 promoter prevents age-dependent transcriptional repression of mps-2 and memory decline. Finally, MPS-2 acts through the modulation of the Kv2.1/KVS-3 and Kv2.2/KVS-4 heteromeric potassium channels. Altogether, we describe a conserved MPS-2/KVS-3/KVS-4 pathway essential for LTAM and also for a programmed control of physiological age-dependent memory decline.
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Affiliation(s)
- Bank G Fenyves
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Department of Molecular Biology, Semmelweis University, Tűzoltó u. 37-47, 1094 Budapest, Hungary
| | - Andreas Arnold
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland
| | - Vaibhav G Gharat
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland
| | - Carmen Haab
- Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland
| | - Kiril Tishinov
- Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland
| | - Fabian Peter
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland
| | - Dominique de Quervain
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Cognitive Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; University Psychiatric Clinics, University of Basel, Wilhelm Klein-Strasse 27, 4055 Basel, Switzerland
| | - Andreas Papassotiropoulos
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Biozentrum, Life Sciences Training Facility, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland; University Psychiatric Clinics, University of Basel, Wilhelm Klein-Strasse 27, 4055 Basel, Switzerland
| | - Attila Stetak
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; University Psychiatric Clinics, University of Basel, Wilhelm Klein-Strasse 27, 4055 Basel, Switzerland.
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9
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Jara JH, Sheets PL, Nigro MJ, Perić M, Brooks C, Heller DB, Martina M, Andjus PR, Ozdinler PH. The Electrophysiological Determinants of Corticospinal Motor Neuron Vulnerability in ALS. Front Mol Neurosci 2020; 13:73. [PMID: 32508590 PMCID: PMC7248374 DOI: 10.3389/fnmol.2020.00073] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Accepted: 04/15/2020] [Indexed: 12/12/2022] Open
Abstract
The brain is complex and heterogeneous. Even though numerous independent studies indicate cortical hyperexcitability as a potential contributor to amyotrophic lateral sclerosis (ALS) pathology, the mechanisms that are responsible for upper motor neuron (UMN) vulnerability remain elusive. To reveal the electrophysiological determinants of corticospinal motor neuron (CSMN, a.k.a UMN in mice) vulnerability, we investigated the motor cortex of hSOD1G93A mice at P30 (postnatal day 30), a presymptomatic time point. Glutamate uncaging by laser scanning photostimulation (LSPS) revealed altered dynamics especially within the inhibitory circuitry and more specifically in L2/3 of the motor cortex, whereas the excitatory microcircuits were unchanged. Observed microcircuitry changes were specific to CSMN in the motor column. Electrophysiological evaluation of the intrinsic properties in response to the microcircuit changes, as well as the exon microarray expression profiles of CSMN isolated from hSOD1G93A and healthy mice at P30, revealed the presence of a very dynamic set of events, ultimately directed to establish, maintain and retain the balance at this early stage. Also, the expression profile of key voltage-gated potassium and sodium channel subunits as well as of the inhibitory GABA receptor subunits and modulatory proteins began to suggest the challenges CSMN face at this early age. Since neurodegeneration is initiated when neurons can no longer maintain balance, the complex cellular events that occur at this critical time point help reveal how CSMN try to cope with the challenges of disease manifestation. This information is critically important for the proper modulation of UMNs and for developing effective treatment strategies.
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Affiliation(s)
- Javier H Jara
- Davee Department of Neurology and Clinical Neurological Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Patrick L Sheets
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Maximiliano José Nigro
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Mina Perić
- Institute for Physiology and Biochemistry "Ivan Djaja", Faculty of Biology, University of Belgrade, Belgrade, Serbia
| | - Carolyn Brooks
- Davee Department of Neurology and Clinical Neurological Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Daniel B Heller
- Davee Department of Neurology and Clinical Neurological Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Marco Martina
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Pavle R Andjus
- Institute for Physiology and Biochemistry "Ivan Djaja", Faculty of Biology, University of Belgrade, Belgrade, Serbia
| | - P Hande Ozdinler
- Davee Department of Neurology and Clinical Neurological Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
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10
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Sandercock DA, Barnett MW, Coe JE, Downing AC, Nirmal AJ, Di Giminiani P, Edwards SA, Freeman TC. Transcriptomics Analysis of Porcine Caudal Dorsal Root Ganglia in Tail Amputated Pigs Shows Long-Term Effects on Many Pain-Associated Genes. Front Vet Sci 2019; 6:314. [PMID: 31620455 PMCID: PMC6760028 DOI: 10.3389/fvets.2019.00314] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Accepted: 09/03/2019] [Indexed: 12/24/2022] Open
Abstract
Tail amputation by tail docking or as an extreme consequence of tail biting in commercial pig production potentially has serious implications for animal welfare. Tail amputation causes peripheral nerve injury that might be associated with lasting chronic pain. The aim of this study was to investigate the short- and long-term effects of tail amputation in pigs on caudal DRG gene expression at different stages of development, particularly in relation to genes associated with nociception and pain. Microarrays were used to analyse whole DRG transcriptomes from tail amputated and sham-treated pigs 1, 8, and 16 weeks following tail treatment at either 3 or 63 days of age (8 pigs/treatment/age/time after treatment; n = 96). Tail amputation induced marked changes in gene expression (up and down) compared to sham-treated intact controls for all treatment ages and time points after tail treatment. Sustained changes in gene expression in tail amputated pigs were still evident 4 months after tail injury. Gene correlation network analysis revealed two co-expression clusters associated with amputation: Cluster A (759 down-regulated) and Cluster B (273 up-regulated) genes. Gene ontology (GO) enrichment analysis identified 124 genes in Cluster A and 61 genes in Cluster B associated with both “inflammatory pain” and “neuropathic pain.” In Cluster A, gene family members of ion channels e.g., voltage-gated potassium channels (VGPC) and receptors e.g., GABA receptors, were significantly down-regulated compared to shams, both of which are linked to increased peripheral nerve excitability after axotomy. Up-regulated gene families in Cluster B were linked to transcriptional regulation, inflammation, tissue remodeling, and regulatory neuropeptide activity. These findings, demonstrate that tail amputation causes sustained transcriptomic expression changes in caudal DRG cells involved in inflammatory and neuropathic pain pathways.
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Affiliation(s)
- Dale A Sandercock
- Animal and Veterinary Science Research Group, Scotland's Rural College, Roslin Institute Building, Edinburgh, United Kingdom
| | - Mark W Barnett
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh, United Kingdom
| | - Jennifer E Coe
- Animal and Veterinary Science Research Group, Scotland's Rural College, Roslin Institute Building, Edinburgh, United Kingdom
| | - Alison C Downing
- Edinburgh Genomics, The University of Edinburgh, Edinburgh, United Kingdom
| | - Ajit J Nirmal
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh, United Kingdom
| | - Pierpaolo Di Giminiani
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Sandra A Edwards
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Tom C Freeman
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh, United Kingdom
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11
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Montalbetti N, Rooney JG, Rued AC, Carattino MD. Molecular determinants of afferent sensitization in a rat model of cystitis with urothelial barrier dysfunction. J Neurophysiol 2019; 122:1136-1146. [PMID: 31314637 DOI: 10.1152/jn.00306.2019] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The internal surface of the urinary bladder is covered by the urothelium, a stratified epithelium that forms an impermeable barrier to urinary solutes. Increased urothelial permeability is thought to contribute to symptom generation in several forms of cystitis by sensitizing bladder afferents. In this report we investigate the physiological mechanisms that mediate bladder afferent hyperexcitability in a rat model of cystitis induced by overexpression in the urothelium of claudin-2 (Cldn2), a tight junction-associated protein upregulated in bladder biopsies from patients with interstitial cystitis/bladder pain syndrome. Patch-clamp studies showed that overexpression of Cldn2 in the urothelium sensitizes a population of isolectin GS-IB4-negative [IB4(-)] bladder sensory neurons with tetrodotoxin-sensitive (TTX-S) action potentials. Gene expression analysis revealed a significant increase in mRNA levels of the delayed-rectifier voltage-gated K+ channel (Kv)2.2 and the accessory subunit Kv9.1 in this population of bladder sensory neurons. Consistent with this finding, Kv2/Kv9.1 channel activity was greater in IB4(-) bladder sensory neurons from rats overexpressing Cldn2 in the urothelium than in control counterparts. Likewise, current density of TTX-S voltage-gated Na+ (Nav) channels was greater in sensitized neurons than in control counterparts. Significantly, guangxitoxin-1E (GxTX-1E), a selective blocker of Kv2 channels, blunted the repetitive firing of sensitized IB4(-) sensory neurons. In summary, our studies indicate that an increase in the activity of TTX-S Nav and Kv2/Kv9.1 channels mediates repetitive firing of sensitized bladder sensory neurons in rats with increased urothelial permeability.NEW & NOTEWORTHY Hyperexcitability of sensitized bladder sensory neurons in a rat model of interstitial cystitis/bladder pain syndrome (IC/BPS) results from increased activity of tetrodotoxin-sensitive voltage-gated Na+ and delayed-rectifier voltage-gated K+ (Kv)2/Kv9.1 channels. Of major significance, our studies indicate that Kv2/Kv9.1 channels play a major role in symptom generation in this model of IC/BPS by maintaining the sustained firing of the sensitized bladder sensory neurons.
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Affiliation(s)
- Nicolas Montalbetti
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - James G Rooney
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Anna C Rued
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Marcelo D Carattino
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.,Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
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12
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Guelfi S, Botia JA, Thom M, Ramasamy A, Perona M, Stanyer L, Martinian L, Trabzuni D, Smith C, Walker R, Ryten M, Reimers M, Weale ME, Hardy J, Matarin M. Transcriptomic and genetic analyses reveal potential causal drivers for intractable partial epilepsy. Brain 2019; 142:1616-1630. [DOI: 10.1093/brain/awz074] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Revised: 12/10/2018] [Accepted: 01/31/2019] [Indexed: 01/05/2023] Open
Affiliation(s)
- Sebastian Guelfi
- Department of Molecular Neuroscience, UCL, Institute of Neurology, Queen Square, London, UK
| | - Juan A. Botia
- Department of Molecular Neuroscience, UCL, Institute of Neurology, Queen Square, London, UK
- Departamento de Ingeniería de la Información y las Comunicaciones, Universidad de Murcia, Murcia, Spain
| | - Maria Thom
- Division of Neuropathology, UCL Institute of Neurology, National Hospital for Neurology and Neurosurgery, London, UK
| | | | - Marina Perona
- Department of Radiobiology (CAC), National Atomic Energy Commission (CNEA), National Scientific and Technical Research Council (CONICET), Argentina
| | - Lee Stanyer
- Department of Molecular Neuroscience, UCL, Institute of Neurology, Queen Square, London, UK
| | - Lillian Martinian
- Departamento de Ingeniería de la Información y las Comunicaciones, Universidad de Murcia, Murcia, Spain
| | - Daniah Trabzuni
- Department of Molecular Neuroscience, UCL, Institute of Neurology, Queen Square, London, UK
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | - Colin Smith
- Academic Department of Neuropathology, Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK
| | - Robert Walker
- Academic Department of Neuropathology, Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK
| | - Mina Ryten
- Department of Molecular Neuroscience, UCL, Institute of Neurology, Queen Square, London, UK
| | - Mark Reimers
- Neuroscience Program and Biomedical Engineering, Michigan State University, East Lansing, MI, USA
| | - Michael E. Weale
- Department Medical and Molecular Genetics, King’s College London, London, UK
| | - John Hardy
- Department of Molecular Neuroscience, UCL, Institute of Neurology, Queen Square, London, UK
| | - Mar Matarin
- Department of Molecular Neuroscience, UCL, Institute of Neurology, Queen Square, London, UK
- Department of Clinical and Experimental Epilepsy, Institute of Neurology, Queen Square, London, WC1N 3, UK
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13
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Pisupati A, Mickolajczyk KJ, Horton W, van Rossum DB, Anishkin A, Chintapalli SV, Li X, Chu-Luo J, Busey G, Hancock WO, Jegla T. The S6 gate in regulatory Kv6 subunits restricts heteromeric K + channel stoichiometry. J Gen Physiol 2018; 150:1702-1721. [PMID: 30322883 PMCID: PMC6279357 DOI: 10.1085/jgp.201812121] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 07/03/2018] [Accepted: 09/26/2018] [Indexed: 11/24/2022] Open
Abstract
Atypical substitutions in the S6 activation gate sequence distinguish “regulatory” Kv subunits, which cannot homotetramerize due to T1 self-incompatibility. Pisupati et al. show that such substitutions in Kv6 work together with self-incompatibility to restrict Kv2:Kv6 heteromeric stoichiometry to 3:1. The Shaker-like family of voltage-gated K+ channels comprises four functionally independent gene subfamilies, Shaker (Kv1), Shab (Kv2), Shaw (Kv3), and Shal (Kv4), each of which regulates distinct aspects of neuronal excitability. Subfamily-specific assembly of tetrameric channels is mediated by the N-terminal T1 domain and segregates Kv1–4, allowing multiple channel types to function independently in the same cell. Typical Shaker-like Kv subunits can form functional channels as homotetramers, but a group of mammalian Kv2-related genes (Kv5.1, Kv6s, Kv8s, and Kv9s) encodes subunits that have a “silent” or “regulatory” phenotype characterized by T1 self-incompatibility. These channels are unable to form homotetramers, but instead heteromerize with Kv2.1 or Kv2.2 to diversify the functional properties of these delayed rectifiers. While T1 self-incompatibility predicts that these heterotetramers could contain up to two regulatory (R) subunits, experiments show a predominance of 3:1R stoichiometry in which heteromeric channels contain a single regulatory subunit. Substitution of the self-compatible Kv2.1 T1 domain into the regulatory subunit Kv6.4 does not alter the stoichiometry of Kv2.1:Kv6.4 heteromers. Here, to identify other channel structures that might be responsible for favoring the 3:1R stoichiometry, we compare the sequences of mammalian regulatory subunits to independently evolved regulatory subunits from cnidarians. The most widespread feature of regulatory subunits is the presence of atypical substitutions in the highly conserved consensus sequence of the intracellular S6 activation gate of the pore. We show that two amino acid substitutions in the S6 gate of the regulatory subunit Kv6.4 restrict the functional stoichiometry of Kv2.1:Kv6.4 to 3:1R by limiting the formation and function of 2:2R heteromers. We propose a two-step model for the evolution of the asymmetric 3:1R stoichiometry, which begins with evolution of self-incompatibility to establish the regulatory phenotype, followed by drift of the activation gate consensus sequence under relaxed selection to limit stoichiometry to 3:1R.
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Affiliation(s)
- Aditya Pisupati
- Department of Biology, Pennsylvania State University, University Park, PA.,Medical Scientist Training Program, College of Medicine, Pennsylvania State University, Hershey, PA
| | - Keith J Mickolajczyk
- Department of Biomedical Engineering, Pennsylvania State University, University Park, PA
| | - William Horton
- Department of Animal Science, Pennsylvania State University, University Park, PA
| | - Damian B van Rossum
- The Jake Gittlen Laboratories for Cancer Research, College of Medicine, Pennsylvania State University, Hershey, PA.,Division of Experimental Pathology, Department of Pathology, College of Medicine, Pennsylvania State University, Hershey, PA
| | - Andriy Anishkin
- Department of Biology, University of Maryland, College Park, MD
| | - Sree V Chintapalli
- Arkansas Children's Nutrition Center and Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, AR
| | - Xiaofan Li
- Department of Biology, Pennsylvania State University, University Park, PA
| | - Jose Chu-Luo
- Department of Biology, Pennsylvania State University, University Park, PA
| | - Gregory Busey
- Department of Biology, Pennsylvania State University, University Park, PA
| | - William O Hancock
- Department of Biomedical Engineering, Pennsylvania State University, University Park, PA
| | - Timothy Jegla
- Department of Biology, Pennsylvania State University, University Park, PA .,Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA
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14
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15
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Bocksteins E. Kv5, Kv6, Kv8, and Kv9 subunits: No simple silent bystanders. J Gen Physiol 2016; 147:105-25. [PMID: 26755771 PMCID: PMC4727947 DOI: 10.1085/jgp.201511507] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 12/11/2015] [Indexed: 12/19/2022] Open
Abstract
Members of the electrically silent voltage-gated K(+) (Kv) subfamilies (Kv5, Kv6, Kv8, and Kv9, collectively identified as electrically silent voltage-gated K(+) channel [KvS] subunits) do not form functional homotetrameric channels but assemble with Kv2 subunits into heterotetrameric Kv2/KvS channels with unique biophysical properties. Unlike the ubiquitously expressed Kv2 subunits, KvS subunits show a more restricted expression. This raises the possibility that Kv2/KvS heterotetramers have tissue-specific functions, making them potential targets for the development of novel therapeutic strategies. Here, I provide an overview of the expression of KvS subunits in different tissues and discuss their proposed role in various physiological and pathophysiological processes. This overview demonstrates the importance of KvS subunits and Kv2/KvS heterotetramers in vivo and the importance of considering KvS subunits and Kv2/KvS heterotetramers in the development of novel treatments.
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Affiliation(s)
- Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology, and Pharmacology, Department for Biomedical Sciences, University of Antwerp, 2610 Antwerp, Belgium
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16
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Kv2 dysfunction after peripheral axotomy enhances sensory neuron responsiveness to sustained input. Exp Neurol 2013; 251:115-26. [PMID: 24252178 PMCID: PMC3898477 DOI: 10.1016/j.expneurol.2013.11.011] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2013] [Revised: 10/21/2013] [Accepted: 11/07/2013] [Indexed: 12/16/2022]
Abstract
Peripheral nerve injuries caused by trauma are associated with increased sensory neuron excitability and debilitating chronic pain symptoms. Axotomy-induced alterations in the function of ion channels are thought to largely underlie the pathophysiology of these phenotypes. Here, we characterise the mRNA distribution of Kv2 family members in rat dorsal root ganglia (DRG) and describe a link between Kv2 function and modulation of sensory neuron excitability. Kv2.1 and Kv2.2 were amply expressed in cells of all sizes, being particularly abundant in medium-large neurons also immunoreactive for neurofilament-200. Peripheral axotomy led to a rapid, robust and long-lasting transcriptional Kv2 downregulation in the DRG, correlated with the onset of mechanical and thermal hypersensitivity. The consequences of Kv2 loss-of-function were subsequently investigated in myelinated neurons using intracellular recordings on ex vivo DRG preparations. In naïve neurons, pharmacological Kv2.1/Kv2.2 inhibition by stromatoxin-1 (ScTx) resulted in shortening of action potential (AP) after-hyperpolarization (AHP). In contrast, ScTx application on axotomized neurons did not alter AHP duration, consistent with the injury-induced Kv2 downregulation. In accordance with a shortened AHP, ScTx treatment also reduced the refractory period and improved AP conduction to the cell soma during high frequency stimulation. These results suggest that Kv2 downregulation following traumatic nerve lesion facilitates greater fidelity of repetitive firing during prolonged input and thus normal Kv2 function is postulated to limit neuronal excitability. In summary, we have profiled Kv2 expression in sensory neurons and provide evidence for the contribution of Kv2 dysfunction in the generation of hyperexcitable phenotypes encountered in chronic pain states. Kv2.1 and Kv2.2 are expressed in rat dorsal root ganglion neurons. Kv2 subunits are most abundant in myelinated sensory neurons. Kv2.1 and Kv.2 subunits are downregulated in a traumatic nerve injury pain model. Kv2 inhibition ex vivo allows higher firing rates during sustained stimulation. We conclude that Kv2 channels contribute to limiting peripheral neuron excitability.
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17
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Tang YQ, Liang P, Zhou J, Lu Y, Lei L, Bian X, Wang K. Auxiliary KChIP4a suppresses A-type K+ current through endoplasmic reticulum (ER) retention and promoting closed-state inactivation of Kv4 channels. J Biol Chem 2013; 288:14727-41. [PMID: 23576435 DOI: 10.1074/jbc.m113.466052] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
In the brain and heart, auxiliary Kv channel-interacting proteins (KChIPs) co-assemble with pore-forming Kv4 α-subunits to form a native K(+) channel complex and regulate the expression and gating properties of Kv4 currents. Among the KChIP1-4 members, KChIP4a exhibits a unique N terminus that is known to suppress Kv4 function, but the underlying mechanism of Kv4 inhibition remains unknown. Using a combination of confocal imaging, surface biotinylation, and electrophysiological recordings, we identified a novel endoplasmic reticulum (ER) retention motif, consisting of six hydrophobic and aliphatic residues, 12-17 (LIVIVL), within the KChIP4a N-terminal KID, that functions to reduce surface expression of Kv4-KChIP complexes. This ER retention capacity is transferable and depends on its flanking location. In addition, adjacent to the ER retention motif, the residues 19-21 (VKL motif) directly promote closed-state inactivation of Kv4.3, thus leading to an inhibition of channel current. Taken together, our findings demonstrate that KChIP4a suppresses A-type Kv4 current via ER retention and enhancement of Kv4 closed-state inactivation.
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Affiliation(s)
- Yi-Quan Tang
- Department of Neurobiology, Neuroscience Research Institute, Peking University Health Science Center, Peking University School of Pharmaceutical Sciences, Beijing 100191, China
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18
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Jegla T, Marlow HQ, Chen B, Simmons DK, Jacobo SM, Martindale MQ. Expanded functional diversity of shaker K(+) channels in cnidarians is driven by gene expansion. PLoS One 2012; 7:e51366. [PMID: 23251506 PMCID: PMC3519636 DOI: 10.1371/journal.pone.0051366] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Accepted: 10/29/2012] [Indexed: 12/27/2022] Open
Abstract
The genome of the cnidarian Nematostella vectensis (starlet sea anemone) provides a molecular genetic view into the first nervous systems, which appeared in a late common ancestor of cnidarians and bilaterians. Nematostella has a surprisingly large and diverse set of neuronal signaling genes including paralogs of most neuronal signaling molecules found in higher metazoans. Several ion channel gene families are highly expanded in the sea anemone, including three subfamilies of the Shaker K+ channel gene family: Shaker (Kv1), Shaw (Kv3) and Shal (Kv4). In order to better understand the physiological significance of these voltage-gated K+ channel expansions, we analyzed the function of 18 members of the 20 gene Shaker subfamily in Nematostella. Six of the Nematostella Shaker genes express functional homotetrameric K+ channels in vitro. These include functional orthologs of bilaterian Shakers and channels with an unusually high threshold for voltage activation. We identified 11 Nematostella Shaker genes with a distinct “silent” or “regulatory” phenotype; these encode subunits that function only in heteromeric channels and serve to further diversify Nematostella Shaker channel gating properties. Subunits with the regulatory phenotype have not previously been found in the Shaker subfamily, but have evolved independently in the Shab (Kv2) family in vertebrates and the Shal family in a cnidarian. Phylogenetic analysis indicates that regulatory subunits were present in ancestral cnidarians, but have continued to diversity at a high rate after the split between anthozoans and hydrozoans. Comparison of Shaker family gene complements from diverse metazoan species reveals frequent, large scale duplication has produced highly unique sets of Shaker channels in the major metazoan lineages.
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Affiliation(s)
- Timothy Jegla
- Department of Biology and Huck Institute of Life Sciences, Eberly College of Science, Penn State University, University Park, PA, USA.
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19
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Smith KE, Wilkie SE, Tebbs-Warner JT, Jarvis BJ, Gallasch L, Stocker M, Hunt DM. Functional analysis of missense mutations in Kv8.2 causing cone dystrophy with supernormal rod electroretinogram. J Biol Chem 2012; 287:43972-83. [PMID: 23115240 DOI: 10.1074/jbc.m112.388033] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Mutations in KCNV2 have been proposed as the molecular basis for cone dystrophy with supernormal rod electroretinogram. KCNV2 codes for the modulatory voltage-gated potassium channel α-subunit, Kv8.2, which is incapable of forming functional channels on its own. Functional heteromeric channels are however formed with Kv2.1 in heterologous expression systems, with both α-subunit genes expressed in rod and cone photoreceptors. Of the 30 mutations identified in the KCNV2 gene, we have selected three missense mutations localized in the potassium channel pore and two missense mutations localized in the tetramerization domain for analysis. We characterized the differences between homomeric Kv2.1 and heteromeric Kv2.1/Kv8.2 channels and investigated the influence of the selected mutations on the function of heteromeric channels. We found that two pore mutations (W467G and G478R) led to the formation of nonconducting heteromeric Kv2.1/Kv8.2 channels, whereas the mutations localized in the tetramerization domain prevented heteromer generation and resulted in the formation of homomeric Kv2.1 channels only. Consequently, our study suggests the existence of two distinct molecular mechanisms involved in the disease pathology.
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Affiliation(s)
- Katie E Smith
- University College London Institute of Ophthalmology, London EC1V 9EL, United Kingdom
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20
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Bocksteins E, Snyders DJ. Electrically Silent Kv Subunits: Their Molecular and Functional Characteristics. Physiology (Bethesda) 2012; 27:73-84. [DOI: 10.1152/physiol.00023.2011] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Electrically silent voltage-gated potassium (KvS) α-subunits do not form homotetramers but heterotetramerize with Kv2 subunits, generating functional Kv2/KvS channel complexes in which the KvS subunits modulate the Kv2 current. This poses intriguing questions into the molecular mechanisms by which these KvS subunits cannot form functional homotetramers, why they only interact with Kv2 subunits, and how they modulate the Kv2 current.
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Affiliation(s)
- Elke Bocksteins
- Department of Biomedical Sciences, Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerpen, Belgium
| | - Dirk J. Snyders
- Department of Biomedical Sciences, Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerpen, Belgium
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21
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Moulton G, Attwood TK, Parry-Smith DJ, Packer JCL. Phylogenomic Analysis and Evolution of the Potassium Channel Gene Family. ACTA ACUST UNITED AC 2011; 9:363-77. [PMID: 14698964 DOI: 10.3109/714041017] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Potassium channels govern the permeability of cells to potassium ions, thereby controlling the membrane potential. In metazoa, potassium channels are encoded by a large, diverse gene family. Previous analyses of this gene family have focused on its diversity in mammals. Here we have pursued a more comprehensive study in Caenorhabditis elegans, Drosophila melanogaster, and mammalian genomes. The investigation revealed 164 potassium channel encoding genes in C. elegans, D. melanogaster, and mammals, classified into seven conserved families, which we applied to phylogenetic analysis. The trees are discussed in relation to the assignment of orthologous relationships between genes and vertebrate genome duplication.
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Affiliation(s)
- G Moulton
- School of Biological Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, United Kingdom.
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22
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Hristov KL, Chen M, Soder RP, Parajuli SP, Cheng Q, Kellett WF, Petkov GV. KV2.1 and electrically silent KV channel subunits control excitability and contractility of guinea pig detrusor smooth muscle. Am J Physiol Cell Physiol 2011; 302:C360-72. [PMID: 21998137 DOI: 10.1152/ajpcell.00303.2010] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Voltage-gated K(+) (K(V)) channels are implicated in detrusor smooth muscle (DSM) function. However, little is known about the functional role of the heterotetrameric K(V) channels in DSM. In this report, we provide molecular, electrophysiological, and functional evidence for the presence of K(V)2.1 and electrically silent K(V) channel subunits in guinea pig DSM. Stromatoxin-1 (ScTx1), a selective inhibitor of the homotetrameric K(V)2.1, K(V)2.2, and K(V)4.2 as well as the heterotetrameric K(V)2.1/6.3 and K(V)2.1/9.3 channels, was used to examine the role of these K(V) channels in DSM function. RT-PCR indicated mRNA expression of K(V)2.1, K(V)6.2-6.3, K(V)8.2, and K(V)9.1-9.3 subunits in isolated DSM cells. K(V)2.1 protein expression was confirmed by Western blot and immunocytochemistry. Perforated whole cell patch-clamp experiments revealed that ScTx1 (100 nM) inhibited the amplitude of the K(V) current in freshly isolated DSM cells. ScTx1 (100 nM) did not significantly change the steady-state activation and inactivation curves for K(V) current. However, ScTx1 (100 nM) decreased the activation time-constant of the K(V) current at positive voltages. Although our patch-clamp data could not exclude the presence of the homotetrameric K(V)2.1 channels, the biophysical characteristics of the ScTx1-sensitive current were consistent with the presence of heterotetrameric K(V)2.1/silent K(V) channels. Current-clamp recordings showed that ScTx1 (100 nM) did not change the DSM cell resting membrane potential. ScTx1 (100 nM) increased the spontaneous phasic contraction amplitude, muscle force, and muscle tone as well as the amplitude of the electrical field stimulation-induced contractions of isolated DSM strips. Collectively, our data revealed that K(V)2.1-containing channels are important physiological regulators of guinea pig DSM excitability and contractility.
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Affiliation(s)
- Kiril L Hristov
- Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, USA
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23
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Dassau L, Conti LR, Radeke CM, Ptáček LJ, Vandenberg CA. Kir2.6 regulates the surface expression of Kir2.x inward rectifier potassium channels. J Biol Chem 2011; 286:9526-41. [PMID: 21209095 DOI: 10.1074/jbc.m110.170597] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Precise trafficking, localization, and activity of inward rectifier potassium Kir2 channels are important for shaping the electrical response of skeletal muscle. However, how coordinated trafficking occurs to target sites remains unclear. Kir2 channels are tetrameric assemblies of Kir2.x subunits. By immunocytochemistry we show that endogenous Kir2.1 and Kir2.2 are localized at the plasma membrane and T-tubules in rodent skeletal muscle. Recently, a new subunit, Kir2.6, present in human skeletal muscle, was identified as a gene in which mutations confer susceptibility to thyrotoxic hypokalemic periodic paralysis. Here we characterize the trafficking and interaction of wild type Kir2.6 with other Kir2.x in COS-1 cells and skeletal muscle in vivo. Immunocytochemical and electrophysiological data demonstrate that Kir2.6 is largely retained in the endoplasmic reticulum, despite high sequence identity with Kir2.2 and conserved endoplasmic reticulum and Golgi trafficking motifs shared with Kir2.1 and Kir2.2. We identify amino acids responsible for the trafficking differences of Kir2.6. Significantly, we show that Kir2.6 subunits can coassemble with Kir2.1 and Kir2.2 in vitro and in vivo. Notably, this interaction limits the surface expression of both Kir2.1 and Kir2.2. We provide evidence that Kir2.6 functions as a dominant negative, in which incorporation of Kir2.6 as a subunit in a Kir2 channel heterotetramer reduces the abundance of Kir2 channels on the plasma membrane.
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Affiliation(s)
- Lior Dassau
- Department of Molecular, Cellular, and Developmental Biology and the Neuroscience Research Institute, University of California, Santa Barbara, California 93106, USA
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Bähring R, Covarrubias M. Mechanisms of closed-state inactivation in voltage-gated ion channels. J Physiol 2010; 589:461-79. [PMID: 21098008 DOI: 10.1113/jphysiol.2010.191965] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Inactivation of voltage-gated ion channels is an intrinsic auto-regulatory process necessary to govern the occurrence and shape of action potentials and establish firing patterns in excitable tissues. Inactivation may occur from the open state (open-state inactivation, OSI) at strongly depolarized membrane potentials, or from pre-open closed states (closed-state inactivation, CSI) at hyperpolarized and modestly depolarized membrane potentials. Voltage-gated Na(+), K(+), Ca(2+) and non-selective cationic channels utilize both OSI and CSI. Whereas there are detailed mechanistic descriptions of OSI, much less is known about the molecular basis of CSI. Here, we review evidence for CSI in voltage-gated cationic channels (VGCCs) and recent findings that shed light on the molecular mechanisms of CSI in voltage-gated K(+) (Kv) channels. Particularly, complementary observations suggest that the S4 voltage sensor, the S4S5 linker and the main S6 activation gate are instrumental in the installment of CSI in Kv4 channels. According to this hypothesis, the voltage sensor may adopt a distinct conformation to drive CSI and, depending on the stability of the interactions between the voltage sensor and the pore domain, a closed-inactivated state results from rearrangements in the selectivity filter or failure of the activation gate to open. Kv4 channel CSI may efficiently exploit the dynamics of the subthreshold membrane potential to regulate spiking properties in excitable tissues.
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Affiliation(s)
- Robert Bähring
- Zentrum für Experimentelle Medizin, Universitätsklinikum Hamburg-Eppendorf, Hamburg, Germany
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25
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Zhong XZ, Abd-Elrahman KS, Liao CH, El-Yazbi AF, Walsh EJ, Walsh MP, Cole WC. Stromatoxin-sensitive, heteromultimeric Kv2.1/Kv9.3 channels contribute to myogenic control of cerebral arterial diameter. J Physiol 2010; 588:4519-37. [PMID: 20876197 DOI: 10.1113/jphysiol.2010.196618] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Cerebral vascular smooth muscle contractility plays a crucial role in controlling arterial diameter and, thereby, blood flow regulation in the brain. A number of K(+) channels have been suggested to contribute to the regulation of diameter by controlling smooth muscle membrane potential (E(m)) and Ca(2+) influx. Previous studies indicate that stromatoxin (ScTx1)-sensitive, Kv2-containing channels contribute to the control of cerebral arterial diameter at 80 mmHg, but their precise role and molecular composition were not determined. Here, we tested if Kv2 subunits associate with 'silent' subunits from the Kv5, Kv6, Kv8 or Kv9 subfamilies to form heterotetrameric channels that contribute to control of diameter of rat middle cerebral arteries (RMCAs) over a range of intraluminal pressure from 10 to 100 mmHg. The predominant mRNAs expressed by RMCAs encode Kv2.1 and Kv9.3 subunits. Co-localization of Kv2.1 and Kv9.3 proteins at the plasma membrane of dissociated single RMCA myocytes was detected by proximity ligation assay. ScTx1-sensitive native current of RMCA myocytes and Kv2.1/Kv9.3 currents exhibited functional identity based on the similarity of their deactivation kinetics and voltage dependence of activation that were distinct from those of homomultimeric Kv2.1 channels. ScTx1 treatment enhanced the myogenic response of pressurized RMCAs between 40 and 100 mmHg, but this toxin also caused constriction between 10 and 40 mmHg that was not previously observed following inhibition of large conductance Ca(2+)-activated K(+) (BK(Ca)) and Kv1 channels. Taken together, this study defines the molecular basis of Kv2-containing channels and contributes to our understanding of the functional significance of their expression in cerebral vasculature. Specifically, our findings provide the first evidence of heteromultimeric Kv2.1/Kv9.3 channel expression in RMCA myocytes and their distinct contribution to control of cerebral arterial diameter over a wider range of E(m) and transmural pressure than Kv1 or BK(Ca) channels owing to their negative range of voltage-dependent activation.
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Affiliation(s)
- Xi Zoë Zhong
- The Smooth Muscle Research Group, Department of Physiology and Pharmacology, Faculty of Medicine, University of Calgary, 3330 Hospital Drive N.W., Calgary, Alberta, Canada T2N 4N1
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26
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Kihira Y, Hermanstyne TO, Misonou H. Formation of heteromeric Kv2 channels in mammalian brain neurons. J Biol Chem 2010; 285:15048-15055. [PMID: 20202934 DOI: 10.1074/jbc.m109.074260] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The formation of heteromeric tetramers is a common feature of voltage-gated potassium (Kv) channels. This results in the generation of a variety of tetrameric Kv channels that exhibit distinct biophysical and biochemical characteristics. Kv2 delayed rectifier channels are, however, unique exceptions. It has been previously shown that mammalian Kv2.1 and Kv2.2 are localized in distinct domains of neuronal membranes and are not capable of forming heteromeric channels with each other (Hwang, P. M., Glatt, C. E., Bredt, D. S., Yellen, G., and Snyder, S. H. (1992) Neuron 8, 473-481). In this study, we report a novel form of rat Kv2.2, Kv2.2(long), which has not been previously recognized. Our data indicate that Kv2.2(long) is the predominant form of Kv2.2 expressed in cortical pyramidal neurons. In contrast to the previous findings, we also found that rat Kv2.1 and Kv2.2(long) are colocalized in the somata and proximal dendrites of cortical pyramidal neurons and are capable of forming functional heteromeric delayed rectifier channels. Our results suggest that the delayed rectifier currents, which regulate action potential firing, are encoded by heteromeric Kv2 channels in cortical neurons.
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Affiliation(s)
- Yoshitaka Kihira
- Department of Neural and Pain Sciences, Dental School, University of Maryland, Baltimore, Maryland 21201
| | - Tracey O Hermanstyne
- Department of Neural and Pain Sciences, Dental School, University of Maryland, Baltimore, Maryland 21201; Program in Neuroscience, University of Maryland, Baltimore, Maryland 21201
| | - Hiroaki Misonou
- Department of Neural and Pain Sciences, Dental School, University of Maryland, Baltimore, Maryland 21201; Program in Neuroscience, University of Maryland, Baltimore, Maryland 21201.
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Bocksteins E, Labro AJ, Mayeur E, Bruyns T, Timmermans JP, Adriaensen D, Snyders DJ. Conserved negative charges in the N-terminal tetramerization domain mediate efficient assembly of Kv2.1 and Kv2.1/Kv6.4 channels. J Biol Chem 2009; 284:31625-34. [PMID: 19717558 DOI: 10.1074/jbc.m109.039479] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated potassium (Kv) channels are transmembrane tetramers of individual alpha-subunits. Eight different Shaker-related Kv subfamilies have been identified in which the tetramerization domain T1, located on the intracellular N terminus, facilitates and controls the assembly of both homo- and heterotetrameric channels. Only the Kv2 alpha-subunits are able to form heterotetramers with members of the silent Kv subfamilies (Kv5, Kv6, Kv8, and Kv9). The T1 domain contains two subdomains, A and B box, which presumably determine subfamily specificity by preventing incompatible subunits to assemble. In contrast, little is known about the involvement of the A/B linker sequence. Both Kv2 and silent Kv subfamilies contain a fully conserved and negatively charged sequence (CDD) in this linker that is lacking in the other subfamilies. Neutralizing these aspartates in Kv2.1 by mutating them to alanines did not affect the gating properties, but reduced the current density moderately. However, charge reversal arginine substitutions strongly reduced the current density of these homotetrameric mutant Kv2.1 channels and immunocytochemistry confirmed the reduced expression at the plasma membrane. Förster resonance energy transfer measurements using confocal microscopy showed that the latter was not due to impaired trafficking, but to a failure to assemble the tetramer. This was further confirmed with co-immunoprecipitation experiments. The corresponding arginine substitution in Kv6.4 prevented its heterotetrameric interaction with Kv2.1. These results indicate that these aspartates (especially the first one) in the A/B box linker of the T1 domain are required for efficient assembly of both homotetrameric Kv2.1 and heterotetrameric Kv2.1/silent Kv6.4 channels.
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Affiliation(s)
- Elke Bocksteins
- Department of Biomedical Sciences, Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, CDE, Universiteitsplein 1, 2610 Antwerp, Belgium
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Bocksteins E, Raes AL, Van de Vijver G, Bruyns T, Van Bogaert PP, Snyders DJ. Kv2.1 and silent Kv subunits underlie the delayed rectifier K+ current in cultured small mouse DRG neurons. Am J Physiol Cell Physiol 2009; 296:C1271-8. [PMID: 19357235 DOI: 10.1152/ajpcell.00088.2009] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Silent voltage-gated K(+) (K(v)) subunits interact with K(v)2 subunits and primarily modulate the voltage dependence of inactivation of these heterotetrameric channels. Both K(v)2 and silent K(v) subunits are expressed in the mammalian nervous system, but little is known about their expression and function in sensory neurons. This study reports the presence of K(v)2.1, K(v)2.2, and silent subunit K(v)6.1, K(v)8.1, K(v)9.1, K(v)9.2, and K(v)9.3 mRNA in mouse dorsal root ganglia (DRG). Immunocytochemistry confirmed the protein expression of K(v)2.x and K(v)9.x subunits in cultured small DRG neurons. To investigate if K(v)2 and silent K(v) subunits are underlying the delayed rectifier K(+) current (I(K)) in these neurons, K(v)2-mediated currents were isolated by the extracellular application of rStromatoxin-1 (ScTx) or by the intracellular application of K(v)2 antibodies. Both ScTx- and anti-K(v)2.1-sensitive currents displayed two components in their voltage dependence of inactivation. Together, both components accounted for approximately two-thirds of I(K). A comparison with results obtained in heterologous expression systems suggests that one component reflects homotetrameric K(v)2.1 channels, whereas the other component represents heterotetrameric K(v)2.1/silent K(v) channels. These observations support a physiological role for silent K(v) subunits in small DRG neurons.
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Affiliation(s)
- Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerpen 2610, Belgium
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29
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Regulation of the Kv2.1 potassium channel by MinK and MiRP1. J Membr Biol 2009; 228:1-14. [PMID: 19219384 DOI: 10.1007/s00232-009-9154-8] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Accepted: 01/13/2009] [Indexed: 12/17/2022]
Abstract
Kv2.1 is a voltage-gated potassium (Kv) channel alpha-subunit expressed in mammalian heart and brain. MinK-related peptides (MiRPs), encoded by KCNE genes, are single-transmembrane domain ancillary subunits that form complexes with Kv channel alpha-subunits to modify their function. Mutations in human MinK (KCNE1) and MiRP1 (KCNE2) are associated with inherited and acquired forms of long QT syndrome (LQTS). Here, coimmunoprecipitations from rat heart tissue suggested that both MinK and MiRP1 form native cardiac complexes with Kv2.1. In whole-cell voltage-clamp studies of subunits expressed in CHO cells, rat MinK and MiRP1 reduced Kv2.1 current density three- and twofold, respectively; slowed Kv2.1 activation (at +60 mV) two- and threefold, respectively; and slowed Kv2.1 deactivation less than twofold. Human MinK slowed Kv2.1 activation 25%, while human MiRP1 slowed Kv2.1 activation and deactivation twofold. Inherited mutations in human MinK and MiRP1, previously associated with LQTS, were also evaluated. D76N-MinK and S74L-MinK reduced Kv2.1 current density (threefold and 40%, respectively) and slowed deactivation (60% and 80%, respectively). Compared to wild-type human MiRP1-Kv2.1 complexes, channels formed with M54T- or I57T-MiRP1 showed greatly slowed activation (tenfold and fivefold, respectively). The data broaden the potential roles of MinK and MiRP1 in cardiac physiology and support the possibility that inherited mutations in either subunit could contribute to cardiac arrhythmia by multiple mechanisms.
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30
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Mederos Y Schnitzler M, Rinné S, Skrobek L, Renigunta V, Schlichthörl G, Derst C, Gudermann T, Daut J, Preisig-Müller R. Mutation of histidine 105 in the T1 domain of the potassium channel Kv2.1 disrupts heteromerization with Kv6.3 and Kv6.4. J Biol Chem 2008; 284:4695-704. [PMID: 19074135 DOI: 10.1074/jbc.m808786200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The voltage-activated K(+) channel subunit Kv2.1 can form heterotetramers with members of the Kv6 subfamily, generating channels with biophysical properties different from homomeric Kv2.1 channels. The N-terminal tetramerization domain (T1) has been shown previously to play a role in Kv channel assembly, but the mechanisms controlling specific heteromeric assembly are still unclear. In Kv6.x channels the histidine residue of the zinc ion-coordinating C3H1 motif of Kv2.1 is replaced by arginine or valine. Using a yeast two-hybrid assay, we found that substitution of the corresponding histidine 105 in Kv2.1 by valine (H105V) or arginine (H105R) disrupted the interaction of the T1 domain of Kv2.1 with the T1 domains of both Kv6.3 and Kv6.4, whereas interaction of the T1 domain of Kv2.1 with itself was unaffected by this mutation. Using fluorescence resonance energy transfer (FRET), interaction could be detected between the subunits Kv2.1/Kv2.1, Kv2.1/Kv6.3, and Kv2.1/Kv6.4. Reduced FRET signals were obtained after co-expression of Kv2.1(H105V) or Kv2.1(H105R) with Kv6.3 or Kv6.4. Wild-type Kv2.1 but not Kv2.1(H105V) could be co-immunoprecipitated with Kv6.4. Co-expression of dominant-negative mutants of Kv6.3 reduced the current produced Kv2.1, but not of Kv2.1(H105R) mutants. Co-expression of Kv6.3 or Kv6.4 with wt Kv2.1 but not with Kv2.1(H105V) or Kv2.1(H105R) changed the voltage dependence of activation of the channels. Our results suggest that His-105 in the T1 domain of Kv2.1 is required for functional heteromerization with members of the Kv6 subfamily. We conclude from our findings that Kv2.1 and Kv6.x subunits have complementary T1 domains that control selective heteromerization.
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31
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Ionic channel function in action potential generation: current perspective. Mol Neurobiol 2008; 35:129-50. [PMID: 17917103 DOI: 10.1007/s12035-007-8001-0] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2006] [Revised: 11/30/1999] [Accepted: 11/10/2006] [Indexed: 10/23/2022]
Abstract
Over 50 years ago, Hodgkin and Huxley laid down the foundations of our current understanding of ionic channels. An impressive progress has been made during the following years that culminated in the revelation of the details of potassium channel structure. Nevertheless, even today, we cannot separate well currents recorded in central mammalian neurons. Many modern concepts about the function of sodium and potassium currents are based on experiments performed in nonmammalian cells. The recent recognition of the fast delayed rectifier current indicates that we need to reevaluate the biophysical role of sodium and potassium currents. This review will consider high quality voltage clamp data obtained from the soma of central mammalian neurons in the view of our current knowledge about proteins forming ionic channels. Fast sodium currents and three types of outward potassium currents, the delayed rectifier, the subthreshold A-type, and the D-type potassium currents, are discussed here. An updated current classification with biophysical role of each current subtype is provided. This review shows that details of kinetics of both sodium and outward potassium currents differ significantly from the classical descriptions and these differences may be of functional significance.
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32
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Czirják G, Tóth ZE, Enyedi P. Characterization of the Heteromeric Potassium Channel Formed by Kv2.1 and the Retinal Subunit Kv8.2 in Xenopus Oocytes. J Neurophysiol 2007; 98:1213-22. [PMID: 17652418 DOI: 10.1152/jn.00493.2007] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Kv8.2 (KCNV2) subunits do not form homotetrameric potassium channels, although they coassemble with Kv2.1 to constitute functional heteromers. High expression of Kv8.2 was reported in the human retina and its mutations were linked to the visual disorder “cone dystrophy with supernormal rod electroretinogram.” We detected abundant Kv8.2 expression in the photoreceptor layer of mouse retina, where Kv2.1 is also known to be present. When the two subunits were coexpressed in Xenopus oocytes in equal amounts, Kv8.2 abolished the current of Kv2.1. If the proportion of Kv8.2 was reduced then the current of heteromeric channels emerged. Kv8.2 shifted the steady-state activation of Kv2.1 to more negative potentials, without affecting the voltage dependence of inactivation. This gave rise to a window current within the −40 to −10 mV membrane potential range. Ba2+ inhibited the heteromeric channel and shifted its activation to more positive potentials. These electrophysiological and pharmacological properties resemble those of the voltage-gated K+ current (named IKx) described in amphibian retinal rods. Furthermore, oocytes expressing Kv2.1/Kv8.2 developed transient hyperpolarizing overshoots in current-clamp experiments, whereas those expressing only Kv2.1 failed to do so. Similar overshoots are characteristic responses of photoreceptors to light flashes. We demonstrated that Kv8.2 G476D, analogous to a disease-causing human mutation, eliminated Kv2.1 current, if the subunits were coexpressed equally. However, Kv8.2 G476D did not form functional heteromers under any conditions. Therefore we suggest that the custom-tailored current of Kv2.1/Kv8.2 functionally contributes to photoreception, and this is the reason that mutations of Kv8.2 lead to a genetic visual disorder.
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Affiliation(s)
- Gábor Czirják
- Department of Physiology, Semmelweis University of Medicine, P.O. Box 259, Budapest, Hungary H-1444
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Guan D, Tkatch T, Surmeier DJ, Armstrong WE, Foehring RC. Kv2 subunits underlie slowly inactivating potassium current in rat neocortical pyramidal neurons. J Physiol 2007; 581:941-60. [PMID: 17379638 PMCID: PMC2170822 DOI: 10.1113/jphysiol.2007.128454] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We determined the expression of Kv2 channel subunits in rat somatosensory and motor cortex and tested for the contributions of Kv2 subunits to slowly inactivating K+ currents in supragranular pyramidal neurons. Single cell RT-PCR showed that virtually all pyramidal cells expressed Kv2.1 mRNA and approximately 80% expressed Kv2.2 mRNA. Immunocytochemistry revealed striking differences in the distribution of Kv2.1 and Kv2.2 subunits. Kv2.1 subunits were clustered and located on somata and proximal dendrites of all pyramidal cells. Kv2.2 subunits were primarily distributed on large apical dendrites of a subset of pyramidal cells from deep layers. We used two methods for isolating currents through Kv2 channels after excluding contributions from Kv1 subunits: intracellular diffusion of Kv2.1 antibodies through the recording pipette and extracellular application of rStromatoxin-1 (ScTx). The Kv2.1 antibody specifically blocked the slowly inactivating K+ current by 25-50% (at 8 min), demonstrating that Kv2.1 subunits underlie much of this current in neocortical pyramidal neurons. ScTx (300 nM) also inhibited approximately 40% of the slowly inactivating K+ current. We observed occlusion between the actions of Kv2.1 antibody and ScTx. In addition, Kv2.1 antibody- and ScTx-sensitive currents demonstrated similar recovery from inactivation and voltage dependence and kinetics of activation and inactivation. These data indicate that both agents targeted the same channels. Considering the localization of Kv2.1 and 2.2 subunits, currents from truncated dissociated cells are probably dominated by Kv2.1 subunits. Compared with Kv2.1 currents in expression systems, the Kv2.1 current in neocortical pyramidal cells activated and inactivated at relatively negative potentials and was very sensitive to holding potential.
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Affiliation(s)
- D Guan
- Department of Anatomy and Neurobiology, University of Tennessee, 855 Monroe Avenue, Memphis, TN 38163, USA
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MacDonald PE, Joseph JW, Rorsman P. Glucose-sensing mechanisms in pancreatic beta-cells. Philos Trans R Soc Lond B Biol Sci 2006; 360:2211-25. [PMID: 16321791 PMCID: PMC1569593 DOI: 10.1098/rstb.2005.1762] [Citation(s) in RCA: 239] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The appropriate secretion of insulin from pancreatic beta-cells is critically important to the maintenance of energy homeostasis. The beta-cells must sense and respond suitably to postprandial increases of blood glucose, and perturbation of glucose-sensing in these cells can lead to hypoglycaemia or hyperglycaemias and ultimately diabetes. Here, we review beta-cell glucose-sensing with a particular focus on the regulation of cellular excitability and exocytosis. We examine in turn: (i) the generation of metabolic signalling molecules; (ii) the regulation of beta-cell membrane potential; and (iii) insulin granule dynamics and exocytosis. We further discuss the role of well known and putative candidate metabolic signals as regulators of insulin secretion.
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Affiliation(s)
- Patrick E MacDonald
- Duke University Medical Center Sarah W. Stedman Nutrition and Metabolism Center Durham, NC 27704, USA.
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35
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Ottschytsch N, Raes AL, Timmermans JP, Snyders DJ. Domain analysis of Kv6.3, an electrically silent channel. J Physiol 2005; 568:737-47. [PMID: 16096342 PMCID: PMC1464172 DOI: 10.1113/jphysiol.2005.090142] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The subunit Kv6.3 encodes a voltage-gated potassium channel belonging to the group of electrically silent Kv subunits, i.e. subunits that do not form functional homotetrameric channels. The lack of current, caused by retention in the endoplasmic reticulum (ER), was overcome by coexpression with Kv2.1. To investigate whether a specific section of Kv6.3 was responsible for ER retention, we constructed chimeric subunits between Kv6.3 and Kv2.1, and analysed their subcellular localization and functionality. The results demonstrate that the ER retention of Kv6.3 is not caused by the N-terminal A and B box (NAB) domain nor the intracellular N- or C-termini, but rather by the S1-S6 core protein. Introduction of individual transmembrane segments of Kv6.3 in Kv2.1 was tolerated, with the exception of S6. Indeed, introduction of the S6 domain of Kv6.3 in Kv2.1 was enough to cause ER retention, which was due to the C-terminal section of S6. The S4 segment of Kv6.3 could act as a voltage sensor in the Kv2.1 context, albeit with a major hyperpolarizing shift in the voltage dependence of activation and inactivation, apparently caused by the presence of a tyrosine in Kv6.3 instead of a conserved arginine. This study suggests that the silent behaviour of Kv6.3 is largely caused by the C-terminal part of its sixth transmembrane domain that causes ER retention of the subunit.
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Affiliation(s)
- Natacha Ottschytsch
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp (CDE), Universiteitsplein 1, T4.21, 2610 Antwerp, Belgium
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36
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Blaine JT, Taylor AD, Ribera AB. Carboxyl Tail Region of the Kv2.2 Subunit Mediates Novel Developmental Regulation of Channel Density. J Neurophysiol 2004; 92:3446-54. [PMID: 15306626 DOI: 10.1152/jn.00512.2004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Molecular mechanisms underlying the acquisition of stable electrical phenotypes in developing neurons remain poorly defined. As Xenopus embryonic spinal neurons mature, they initially exhibit dramatic changes in excitability due to a threefold increase in voltage-gated potassium current ( IKv) density. Later when mature neurons begin synapse formation, IKvdensity remains stable. Elevation of Kv1.1 and Kv2.1 RNA levels indicates that excess transcript levels of these Kv genes can increase current density in both young and mature neurons. In contrast, Kv2.2 overexpression increases IKvdensity in young but not mature neurons despite the presence of protein translated from injected RNA at this stage. Because protein domains can determine biophysical as well as subcellular localization properties of channel subunits, we tested whether a region of the Kv2.2 subunit regulated functional expression in mature neurons. We focused on the large cytoplasmic carboxy tail, a region that differs most between Kv2.2 and the structurally related Kv2.1 subunit. Chimeric Kv2 subunits were generated in which different regions of the large cytoplasmic carboxyl tail were exchanged between Kv2.1 and Kv2.2 subunits. All chimeric Kv2 subunits induced voltage-gated potassium currents when expressed heterologously in oocytes. In vivo chimeric subunits increased IKvdensity in young neurons on overexpression in the developing embryo. In contrast, in mature neurons, only those chimeras lacking a domain in the proximal carboxy terminus, proxC, increased IKvdensity when overexpressed. Thus the proxC domain mediates developmental and subunit-specific regulation of IKvand identifies a novel function for protein domains.
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Affiliation(s)
- Judith T Blaine
- Department of Physiology and Biophysics, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA
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37
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Vega-Saenz de Miera EC. Modification of Kv2.1 K+ currents by the silent Kv10 subunits. ACTA ACUST UNITED AC 2004; 123:91-103. [PMID: 15046870 DOI: 10.1016/j.molbrainres.2004.01.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/28/2004] [Indexed: 12/13/2022]
Abstract
Human and rat Kv10.1a and b cDNAs encode silent K+ channel pore-forming subunits that modify the electrophysiological properties of Kv2.1. These alternatively spliced variants arise by the usage of an alternative site of splicing in exon 1 producing an 11-amino acid insertion in the linker between the first and second transmembrane domains in Kv10.1b. In human, the Kv10s mRNA were detected by Northern blot in brain kidney lung and pancreas. In brain, they were expressed in cortex, hippocampus, caudate, putamen, amygdala and weakly in substantia nigra. In rat, Kv10.1 products were detected in brain and weakly in testes. In situ hybridization in rat brain shows that Kv10.1 mRNAs are expressed in cortex, olfactory cortical structures, basal ganglia/striatal structures, hippocampus and in many nuclei of the amygdala complex. The CA3 and dentate gyrus of the hippocampus present a gradient that show a progression from high level of expression in the caudo-ventro-medial area to a weak level in the dorso-rostral area. The CA1 and CA2 areas had low levels throughout the hippocampus. Several small nuclei were also labeled in the thalamus, hypothalamus, pons, midbrain, and medulla oblongata. Co-injection of Kv2.1 and Kv10.1a or b mRNAs in Xenopus oocytes produced smaller currents that in the Kv2.1 injected oocytes and a moderate reduction of the inactivation rate without any appreciable change in recovery from inactivation or voltage dependence of activation or inactivation. At higher concentration, Kv10.1a also reduces the activation rate and a more important reduction in the inactivation rate. The gene that encodes for Kv10.1 mRNAs maps to chromosome 2p22.1 in human, 6q12 in rat and 17E4 in mouse, locations consistent with the known systeny for human, rat and mouse chromosomes.
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Piwowarski T, Panofen F, Jeserich G. Molecular cloning and partial functional characterization of Tsha3--a novel modulatory potassium channel alpha-subunit of trout CNS. ACTA ACUST UNITED AC 2004; 124:124-33. [PMID: 15135220 DOI: 10.1016/j.molbrainres.2004.02.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/17/2004] [Indexed: 11/25/2022]
Abstract
A novel Shaker-related potassium channel subunit termed Tsha3 that is widely expressed in the CNS of trout was PCR-cloned and sequenced: its deduced amino acid sequence showed an extended N-terminal domain with a high proportion of negatively charged residues and possessed highest similarity with KCNA10, a human epithelial potassium channel. Upon heterologous expression in Sf21 cells, homomeric Tsha3 did not yield voltage-activated potassium channels but produced only ohmic currents that reversed at -15 mV. After co-expression with Tsha1, a novel outward rectifier current was generated that differed from homomeric Tsha1 by its slower kinetics of activation, its partial current inactivation, and its partial blockade by 5 mM TEA as well as 1 microM DTX. Co-immunoprecipitation studies using anti-Tsha3 antibodies confirmed that Tsha3 tightly bound with Tsha1 in co-infected Sf21 cells. As revealed from GFP- and DsRed-labeling studies, the pattern of distribution of Tsha1 was profoundly altered after co-infection with Tsha3 subunits.
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Affiliation(s)
- Tanja Piwowarski
- Department of Neurobiology, University of Osnabrück, Barbarastr. 11, 49069 Osnabrück, Germany
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Ebihara M, Ohba H, Kikuchi M, Yoshikawa T. Structural characterization and promoter analysis of human potassium channel Kv8.1 (KCNV1) gene. Gene 2004; 325:89-96. [PMID: 14697513 DOI: 10.1016/j.gene.2003.09.044] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The voltage-gated K(+) channel (Kv) family comprises four subfamilies: Kv1, Kv2, Kv3 and Kv4. Kv6, Kv7, Kv8 and Kv9 subfamilies have also recently been reported. The gene for Kv8.1 (KCNV1) maps onto chromosome 8q23.3, a locus for benign adult familial myoclonic epilepsy. Despite sequence identity with other K(+) channel genes, KCNV1 does not display K(+) channel activity when expressed in Xenopus oocytes, instead inhibiting activity of Kv2 and Kv3 channels. The present study investigated the molecular structure of KCNV1. In silico analysis detected a new 5' noncoding exon, which extended the reported cDNA sequence to approximately 600 bp. A promoter motif was found only in the upstream region of the newly detected exon 1. To determine the transcriptional mechanism of KCNV1, we generated a series of deletion mutants and random mutants, and examined promoter activities using the luciferase system. Three Sp1 motifs were found to be active in the core promoter sequence, spanning from nt -1350 to -911 (A of the ATG initiation codon was counted as +1). At least two additional sequences were detected as essential elements for promoter activity. A possible alternative 3' end was also detected at 280 bp downstream from the reported 3' end. These results provide useful information in developing KCNV1 screening for epileptic disease.
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Affiliation(s)
- Mitsuru Ebihara
- Laboratory for Molecular Psychiatry, RIKEN Brain Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
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Chérel I. Regulation of K+ channel activities in plants: from physiological to molecular aspects. JOURNAL OF EXPERIMENTAL BOTANY 2004; 55:337-51. [PMID: 14739260 DOI: 10.1093/jxb/erh028] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Plant voltage-gated channels belonging to the Shaker family participate in sustained K+ transport processes at the cell and whole plant levels, such as K+ uptake from the soil solution, long-distance K+ transport in the xylem and phloem, and K+ fluxes in guard cells during stomatal movements. The attention here is focused on the regulation of these transport systems by protein-protein interactions. Clues to the identity of the regulatory mechanisms have been provided by electrophysiological approaches in planta or in heterologous systems, and through analogies with their animal counterparts. It has been shown that, like their animal homologues, plant voltage-gated channels can assemble as homo- or heterotetramers associating polypeptides encoded by different Shaker genes, and that they can bind auxiliary subunits homologous to those identified in mammals. Furthermore, several regulatory processes (involving, for example, protein kinases and phosphatases, G proteins, 14-3-3s, or syntaxins) might be common to plant and animal Shakers. However, the molecular identification of plant channel partners is still at its beginning. This paper reviews current knowledge on plant K+ channel regulation at the physiological and molecular levels, in the light of the corresponding knowledge in animal cells, and discusses perspectives for the deciphering of regulatory networks in the future.
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Affiliation(s)
- Isabelle Chérel
- Biochimie et Physiologie Moléculaire des Plantes, UMR 5004, Agro-M/INRA/CNRS/UM2, Montpellier, France.
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Mathie A, Clarke CE, Ranatunga KM, Veale EL. What are the roles of the many different types of potassium channel expressed in cerebellar granule cells? CEREBELLUM (LONDON, ENGLAND) 2003; 2:11-25. [PMID: 12882230 DOI: 10.1080/14734220310015593] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Potassium (K) channels have a key role in the regulation of neuronal excitability. Over a hundred different subunits encoding distinct K channel subtypes have been identified so far. A major challenge is to relate these many different channel subunits to the functional K currents observed in native neurons. In this review, we have concentrated on cerebellar granule neurons (CGNs). We have considered each of the three principal super families of K channels in turn, namely, the six transmembrane domain, voltage-gated super family, the two transmembrane domain, inward-rectifier super family and the four transmembrane domain, leak channel super family. For each super family, we have identified the subunits that are expressed in CGNs and related the properties of these expressed channel subunits to the functional currents seen in electrophysiological recordings from these neurons. In some cases, there are strong molecular candidates for proteins underlying observed currents. In other cases the correlation is less clear. We show that at least 26 potassium channel alpha subunits are moderately or strongly expressed in CGNs. Nevertheless, a good empirical model of CGN function has been obtained with just six distinct K conductances. The transient KA current in CGNs, seems due to expression of Kv4.2 channels or Kv4.2/4.3 heteromers, while the KCa current is due to expression of large-conductance slo channels. The G-protein activated KIR current is probably due to heteromeric expression of KIR3.1 and KIR3.2. Perhaps KIR2.2 subunits underlie the KIR current when it is constitutively active. The leak conductance can be attributed to TASK-1 and or TASK-3 channels. With less certainty, the IK-slow current may be due to expression of one or more members of the KCNQ or EAG family. Lastly, the delayed-rectifier Kv current has as many as six different potential contributors from the extensive Kv family of alpha subunits. Since many of these subunits are highly regulated by neurotransmitters, physiological regulators and, often, auxiliary subunits, the resulting electrical properties of CGNs may be highly dynamic and subject to constant fine-tuning.
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Affiliation(s)
- Alistair Mathie
- Biophysics Section, Blackett Laboratory, Department of Biological Sciences, Imperial College of Science Technology and Medicine, London, UK.
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42
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MacDonald PE, Wheeler MB. Voltage-dependent K(+) channels in pancreatic beta cells: role, regulation and potential as therapeutic targets. Diabetologia 2003; 46:1046-62. [PMID: 12830383 DOI: 10.1007/s00125-003-1159-8] [Citation(s) in RCA: 178] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2003] [Revised: 05/23/2003] [Indexed: 01/11/2023]
Abstract
Insulin secretion from pancreatic islet beta cells is acutely regulated by a complex interplay of metabolic and electrogenic events. The electrogenic mechanism regulating insulin secretion from beta cells is commonly referred to as the ATP-sensitive K(+) (K(ATP)) channel dependent pathway. Briefly, an increase in ATP and, perhaps more importantly, a decrease in ADP stimulated by glucose metabolism depolarises the beta cell by closing K(ATP) channels. Membrane depolarisation results in the opening of voltage-dependent Ca(2+) channels, and influx of Ca(2+) is the main trigger for insulin secretion. Repolarisation of pancreatic beta cell action potential is mediated by the activation of voltage-dependent K(+) (Kv) channels. Various Kv channel homologues have been detected in insulin secreting cells, and recent studies have shown a role for specific Kv channels as modulators of insulin secretion. Here we review the evidence supporting a role for Kv channels in the regulation of insulin secretion and discuss the potential and the limitations for beta-cell Kv channels as therapeutic targets. Furthermore, we review recent investigations of mechanisms regulating Kv channels in beta cells, which suggest that Kv channels are active participants in the regulation of beta-cell electrical activity and insulin secretion.
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Affiliation(s)
- P E MacDonald
- Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
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Kerschensteiner D, Monje F, Stocker M. Structural determinants of the regulation of the voltage-gated potassium channel Kv2.1 by the modulatory α-subunit Kv9.3. J Biol Chem 2003; 278:18154-61. [PMID: 12642579 DOI: 10.1074/jbc.m213117200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated potassium (Kv) channels containing alpha-subunits of the Kv2 subfamily mediate delayed rectifier currents in excitable cells. Channels formed by Kv2.1 alpha-subunits inactivate from open- and closed states with both forms of inactivation serving different physiological functions. Here we show that open- and closed-state inactivation of Kv2.1 can be distinguished by the sensitivity to intracellular tetraethylammonium and extracellular potassium and lead to the same inactivated conformation. The functional properties of Kv2.1 are regulated by its association with modulatory alpha-subunits (Kv5, Kv6, Kv8, and Kv9). For instance, Kv9.3 changes the state preference of Kv2.1 inactivation by accelerating closed-state inactivation and inhibiting open-state inactivation. An N-terminal regulatory domain (NRD) has been suggested to determine the function of the modulatory alpha-subunit Kv8.1. However, when we tested the NRD of Kv9.3, we found that the functional properties of chimeric Kv2.1 channels containing the NRD of Kv9.3 (Kv2.1(NRD)) did not resemble those of Kv2.1/Kv9.3 heteromers, thus questioning the role of the NRD in Kv9 subunits. A further region of interest is a PXP motif in the sixth transmembrane segment. This motif is conserved among all alpha-subunits of the Kv1, Kv2, Kv3, and Kv4 subfamilies, whereas the second proline is not conserved in any modulatory alpha-subunit. Exchanging this proline in Kv2.1 for the corresponding residue of Kv9.3 resulted in channels (Kv2.1-P410T) that show all hallmarks of the regulation of Kv2.1 by Kv9.3. The effect prevailed in heteromeric channels following co-expression of Kv2.1-P410T with Kv2.1. These data suggest that the alteration of the PXP motif is an important determinant of the regulatory function of modulatory alpha-subunits.
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Affiliation(s)
- Daniel Kerschensteiner
- Max-Planck Institut für Experimentelle Medizin, Molekulare Biologie Neuronaler Signale, Hermann-Rein Strasse 3, 37075 Göttingen, Germany.
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44
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Sano A, Mikami M, Nakamura M, Ueno SI, Tanabe H, Kaneko S. Positional candidate approach for the gene responsible for benign adult familial myoclonic epilepsy. Epilepsia 2002; 43 Suppl 9:26-31. [PMID: 12383276 DOI: 10.1046/j.1528-1157.43.s.9.7.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Benign adult familial myoclonic epilepsy (BAFME) is an autosomal dominant idiopathic epileptic syndrome characterized by adult-onset tremulous finger movement, myoclonus, epileptic seizures, and nonprogressive course, recognized in Japanese families. We recently assigned the gene locus to chromosome 8q23.3-q24.11 by linkage analysis. In this study, we identified the sequence of human cDNA encoding Kv8.1, a neuronal modulatory alpha-subunit of the voltage-gated potassium channel, mapped to human chromosome 8q22.3-8q24.1. Human Kv8.1 cDNA had a 1,500-nucleotide open reading frame encoding a polypeptide of 500 amino acids, in which six hydrophobic transmembrane segments were well conserved, and its overall amino acids homology as compared with those of rat and golden hamster was 95.0% and 95.0%. Tissue-distribution analysis by reverse transcription-polymerase chain reaction (RT-PCR) showed the presence of the Kv 8.1 transcript exclusively in the brain. The analysis of the genomic organization of the human gene revealed consistency of three exons interrupted by two introns each of 1.2 and 3.5 kb. We analyzed the genomic sequence of the patients with BAFME and found no change in the pathogenesis of the disease.
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Affiliation(s)
- Akira Sano
- Department of Neuropsychiatry, Ehime University School of Medicine, Shigenobu, Onsen-Gun, Ehime, Japan.
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Coma M, Vicente R, Tsevi I, Grande M, Tamkun MM, Felipe A. Different Kv2.1/Kv9.3 heteromer expression during brain and lung post-natal development in the rat. J Physiol Biochem 2002; 58:195-203. [PMID: 12744302 DOI: 10.1007/bf03179857] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
The Kv2.1/Kv9.3 heteromer generates an O2 sensitive potassium channel and induces a slow deactivation that has important consequences for brain and lung physiology. We examined the developmental regulation of Kv2.1 and Kv9.3 mRNAs in brain and lung. Both genes followed parallel expression patterns in brain, increasing progressively through post-natal life. In lung, however, the expression of the two genes followed opposite trends: Kv2.1 transcripts decreased, while Kv9.3 mRNA increased. The Kv9.3/Kv2.1 ratio shows that while in brain the expression of both genes followed a similar pattern, the relative abundance of Kv9.3 increased steadily through post-natal life in lung. Furthermore, there is selective regulation of gene expression during the suckling-weaning transition. Our results suggest that different Kv9.3/Kv2.1 ratios could have physiological implications in both organs during post-natal development, and that diet composition and selective tissue-specific insulin regulation modulate the expression of Kv2.1 and Kv9.3.
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Affiliation(s)
- M Coma
- Laboratori de Fisiologia Molecular, Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, 08028 Barcelona, Spain
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46
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Ottschytsch N, Raes A, Van Hoorick D, Snyders DJ. Obligatory heterotetramerization of three previously uncharacterized Kv channel alpha-subunits identified in the human genome. Proc Natl Acad Sci U S A 2002; 99:7986-91. [PMID: 12060745 PMCID: PMC123007 DOI: 10.1073/pnas.122617999] [Citation(s) in RCA: 122] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Voltage-gated K(+) channels control excitability in neuronal and various other tissues. We identified three unique alpha-subunits of voltage-gated K(+)-channels in the human genome. Analysis of the full-length sequences indicated that one represents a previously uncharacterized member of the Kv6 subfamily, Kv6.3, whereas the others are the first members of two unique subfamilies, Kv10.1 and Kv11.1. Although they have all of the hallmarks of voltage-gated K(+) channel subunits, they did not produce K(+) currents when expressed in mammalian cells. Confocal microscopy showed that Kv6.3, Kv10.1, and Kv11.1 alone did not reach the plasma membrane, but were retained in the endoplasmic reticulum. Yeast two-hybrid experiments failed to show homotetrameric interactions, but showed interactions with Kv2.1, Kv3.1, and Kv5.1. Co-expression of each of the previously uncharacterized subunits with Kv2.1 resulted in plasma membrane localization with currents that differed from typical Kv2.1 currents. This heteromerization was confirmed by co-immunoprecipitation. The Kv2 subfamily consists of only two members and uses interaction with "silent subunits" to diversify its function. Including the subunits described here, the "silent subunits" represent one-third of all Kv subunits, suggesting that obligatory heterotetramer formation is more widespread than previously thought.
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Affiliation(s)
- N Ottschytsch
- Laboratory for Molecular Biophysics, Physiology, and Pharmacology, Department of Biomedical Sciences, University of Antwerp (UIA), Universiteitsplein 1, T4.21 B2610 Antwerp, Belgium
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Alessandri-Haber N, Alcaraz G, Deleuze C, Jullien F, Manrique C, Couraud F, Crest M, Giraud P. Molecular determinants of emerging excitability in rat embryonic motoneurons. J Physiol 2002; 541:25-39. [PMID: 12015418 PMCID: PMC2290306 DOI: 10.1113/jphysiol.2001.013371] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Molecular determinants of excitability were studied in pure cultures of rat embryonic motoneurons. Using RT-PCR, we have shown here that the spike-generating Na(+) current is supported by Nav1.2 and/or Nav1.3 alpha-subunits. Nav1.1 and Nav1.6 transcripts were also identified. We have demonstrated that alternatively spliced isoforms of Nav1.1 and Nav1.6, resulting in truncated proteins, were predominant during the first week in culture. However, Nav1.6 protein could be detected after 12 days in vitro. The Nav beta 2.1 transcript was not detected, whereas the Nav beta 1.1 transcript was present. Even in the absence of Nav beta 2.1, alpha-subunits were correctly inserted into the initial segment. RT-PCR (at semi-quantitative and single-cell levels) and immunocytochemistry showed that transient K(+) currents result from the expression of Kv4.2 and Kv4.3 subunits. This is the first identification of subunits responsible for a transient K(+) current in spinal motoneurons. The blockage of Kv4.2/Kv4.3 using a specific toxin modified the shape of the action potential demonstrating the involvement of these conductance channels in regulating spike repolarization and the discharge frequency. Among the other Kv alpha-subunits (Kv1.3, 1.4, 1.6, 2.1, 3.1 and 3.3), we showed that the Kv1.6 subunit was partly responsible for the sustained K(+) current. In conclusion, this study has established the first correlation between the molecular nature of voltage-dependent Na(+) and K(+) channels expressed in embryonic rat motoneurons in culture and their electrophysiological characteristics in the period when excitability appears.
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Affiliation(s)
- Nicole Alessandri-Haber
- Laboratoire ITIS, CNRS FRE 2362, 31 Chemin Joseph Aiguier, 13402 Marseille, Cedex 20, France
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48
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Sano Y, Mochizuki S, Miyake A, Kitada C, Inamura K, Yokoi H, Nozawa K, Matsushime H, Furuichi K. Molecular cloning and characterization of Kv6.3, a novel modulatory subunit for voltage-gated K(+) channel Kv2.1. FEBS Lett 2002; 512:230-4. [PMID: 11852086 DOI: 10.1016/s0014-5793(02)02267-6] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report identification and characterization of Kv6.3, a novel member of the voltage-gated K(+) channel. Reverse transcriptase-polymerase chain reaction analysis indicated that Kv6.3 was highly expressed in the brain. Electrophysiological studies indicated that homomultimeric Kv6.3 did not yield a functional voltage-gated ion channel. When Kv6.3 and Kv2.1 were co-expressed, the heteromultimeric channels displayed the decreased rate of deactivation compared to the homomultimeric Kv2.1 channels. Immunoprecipitation studies indicated that Kv6.3 bound with Kv2.1 in co-transfected cells. These results indicate that Kv6.3 is a novel member of the voltage-gated K(+) channel which functions as a modulatory subunit.
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Affiliation(s)
- Yorikata Sano
- Molecular Medicine Laboratories, Institute for Drug Discovery Research, Yamanouchi Pharmaceutical Co., Ltd., 21 Miyukigaoka, Ibaraki 305-8585, Tsukuba, Japan.
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Moshelion M, Becker D, Czempinski K, Mueller-Roeber B, Attali B, Hedrich R, Moran N. Diurnal and circadian regulation of putative potassium channels in a leaf moving organ. PLANT PHYSIOLOGY 2002; 128:634-42. [PMID: 11842166 PMCID: PMC148925 DOI: 10.1104/pp.010549] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2001] [Revised: 09/11/2001] [Accepted: 11/02/2001] [Indexed: 05/18/2023]
Abstract
In a search for potassium channels involved in light- and clock-regulated leaf movements, we cloned four putative K channel genes from the leaf-moving organs, pulvini, of the legume Samanea saman. The S. saman SPOCK1 is homologous to KCO1, an Arabidopsis two-pore-domain K channel, the S. saman SPORK1 is similar to SKOR and GORK, Arabidopsis outward-rectifying Shaker-like K channels, and the S. saman SPICK1 and SPICK2 are homologous to AKT2, a weakly-inward-rectifying Shaker-like Arabidopsis K channel. All four S. saman sequences possess the universal K-channel-specific pore signature, TXXTXGYG, strongly suggesting a role in transmembrane K(+) transport. The four S. saman genes had different expression patterns within four leaf parts: "extensor" and "flexor" (the motor tissues), the leaf blades (mainly mesophyll), and the vascular bundle ("rachis"). Based on northern blot analysis, their transcript level was correlated with the rhythmic leaf movements: (a) all four genes were regulated diurnally (Spick2, Spork1, and Spock1 in extensor and flexor, Spick1 in extensor and rachis); (b) Spork1 and Spock1 rhythms were inverted upon the inversion of the day-night cycle; and (c) in extensor and/or flexor, the expression of Spork1, Spick1, and Spick2 was also under a circadian control. These findings parallel the circadian rhythm shown to govern the resting membrane K(+) permeability in extensor and flexor protoplasts and the susceptibility of this permeability to light stimulation (Kim et al., 1993). Thus, Samanea pulvinar motor cells are the first described system combining light and circadian regulation of K channels at the level of transcript and membrane transport.
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Affiliation(s)
- Menachem Moshelion
- University of Potsdam, Department of Biochemistry, Karl-Liebknecht-Strasse 24-25, Haus 20, D-14476 Golm, Germany
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Riazanski V, Becker A, Chen J, Sochivko D, Lie A, Wiestler OD, Elger CE, Beck H. Functional and molecular analysis of transient voltage-dependent K+ currents in rat hippocampal granule cells. J Physiol 2001; 537:391-406. [PMID: 11731573 PMCID: PMC2278961 DOI: 10.1111/j.1469-7793.2001.00391.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. We have investigated voltage-dependent outward K+ currents of dentate granule cells (DGCs) in acute brain slices from young and adult rats using nucleated and outside-out patch recordings. 2. In adult DGCs, the outward current pattern was dominated by a transient K+ current component. One portion of this current (approximately 60%) was blocked by micromolar concentrations of tetraethylammonium (TEA; IC50 42 microM) and BDS-I, a specific blocker of Kv3.4 subunits (2.5 microM). A second component was insensitive to tetraethylammonium (10 mM) and BDS-I. The transient outward current could be completely blocked by 4-aminopyridine (IC50 296 microM). 3. The TEA- and BDS-I-sensitive and the TEA-resistant current components were isolated pharmacologically. The current component that was blocked by BDS-I and TEA showed a depolarized threshold of activation (approximately -30 mV) reminiscent of Kv3.4 subunits, while the current component resistant to TEA activated at more hyperpolarized potentials (approximately -60 mV). 4. In nucleated patches obtained by placing the patch pipette adjacent to the apical dendrite, only small Na+ currents and small BDS-I-sensitive transient currents were detected. Nucleated patches obtained from either the cell soma (see above) or the axon hillock showed significantly larger amplitude Na+ currents as well as larger BDS-I-sensitive currents, indicating that this current was predominantly localized within the axosomatic compartment. This result was in good agreement with the distribution of Kv3.4 protein as determined by immunohistochemistry. 5. Current-clamp as well as mock action potential-clamp experiments revealed that the BDS-sensitive current component contributes to action potential repolarization. 6. A comparison of the two age groups (4-10 days and 60-100 days) revealed a marked developmental up-regulation of the BDS-I-sensitive component. These functional changes are paralleled by a developmental increase in Kv3.4 mRNA expression determined by quantitative real-time RT-PCR, as well as a pronounced up-regulation of Kv3.4 on the protein level determined by immunohistochemistry. 7. These functional and molecular results argue that Kv3.4 channels located predominantly in the axosomatic compartment underlie a transient K+ current in adult DGCs, and that these channels are functionally important for regulating spike repolarization. The marked developmental regulation suggests an important role of Kv3.4 in neuronal maturation.
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Affiliation(s)
- V Riazanski
- Department of Epileptology, University of Bonn Medical Center, Sigmund-Freud Strasse 25, 53105 Bonn, Germany
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