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Dolzer J, Schröder K, Stengl M. Cyclic nucleotide-dependent ionic currents in olfactory receptor neurons of the hawkmoth Manduca sexta suggest pull-push sensitivity modulation. Eur J Neurosci 2021; 54:4804-4826. [PMID: 34128265 DOI: 10.1111/ejn.15346] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Revised: 06/02/2021] [Accepted: 06/04/2021] [Indexed: 11/27/2022]
Abstract
Olfactory receptor neurons (ORNs) of the hawkmoth Manduca sexta sensitize via cAMP- and adapt via cGMP-dependent mechanisms. Perforated patch clamp recordings distinguished 11 currents in these ORNs. Derivatives of cAMP and/or cGMP antagonistically affected three of five K+ currents and two non-specific cation currents. The Ca2+ -dependent K+ current IK(Ca 2+ ) and the sensitive pheromone-dependent K+ current IK(cGMP-) , which both express fast kinetics, were inhibited by 8bcGMP, while a slow K+ current, IK(cGMP+) , was activated by 8bcGMP. Furthermore, application of 8bcAMP blocked slowly activating, zero mV-reversing, non-specific cation currents, ILL and Icat(PKC?) , which remained activated in the presence of 8bcGMP. Their activations pull the membrane potential towards their 0-mV reversal potentials, in addition to increasing intracellular Ca2+ levels voltage- and ILL -dependently. Twenty minutes after application, 8bcGMP blocked a TEA-independent K+ current, IK(noTEA) , and a fast cation current, Icat(nRP) , which both shift the membrane potential to negative values. We conclude that conditions of sensitization are maintained at high levels of cAMP, via specific opening/closure of ion channels that allow for fast kinetics, hyperpolarized membrane potentials, and low intracellular Ca2+ levels. In contrast, adaptation is supported via cGMP, which antagonizes cAMP, opening Ca2+ -permeable channels with slow kinetics that stabilize depolarized resting potentials. The antagonistic modulation of peripheral sensory neurons by cAMP or cGMP is reminiscent of pull-push mechanisms of neuromodulation at central synapses underlying metaplasticity.
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Affiliation(s)
- Jan Dolzer
- Biologie, Tierphysiologie, Philipps-Universität Marburg, Marburg, Germany.,Institut für Zoologie, Universität Regensburg, Regensburg, Germany
| | - Katrin Schröder
- Animal Physiology/Neuroethology, Biology, FB 10, University of Kassel, Kassel, Germany
| | - Monika Stengl
- Biologie, Tierphysiologie, Philipps-Universität Marburg, Marburg, Germany.,Institut für Zoologie, Universität Regensburg, Regensburg, Germany.,Animal Physiology/Neuroethology, Biology, FB 10, University of Kassel, Kassel, Germany
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2
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Immonen EV, French AS, Torkkeli PH, Liu H, Vähäsöyrinki M, Frolov RV. EAG channels expressed in microvillar photoreceptors are unsuited to diurnal vision. J Physiol 2017; 595:5465-5479. [PMID: 28087896 DOI: 10.1113/jp273612] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 12/16/2017] [Indexed: 12/15/2022] Open
Abstract
KEY POINTS The principles underlying the evolutionary selection of ion channels for expression in sensory neurons are unclear. Photoreceptor depolarization in the diurnal Drosophila melanogaster is predominantly provided by light-activated transient receptor potential (TRP) channels, whereas repolarization is mediated by sustained voltage-gated K+ channels of the Shab family. In the present study, we show that phototransduction in the nocturnal cockroach Periplaneta americana is predominantly mediated by TRP-like channels, whereas membrane repolarization is based on EAG channels. Although bright light stimulates Shab channels in Drosophila, further restricting depolarization and improving membrane bandwidth, it strongly suppresses EAG conductance in Periplaneta. This light-dependent inhibition (LDI) is caused by calcium and is abolished by chelating intracellular calcium or suppressing eag gene expression. LDI increases membrane resistance, augments gain and reduces the signalling bandwidth. This makes EAG unsuitable for light response conditioning during the day and might have resulted in the evolutionary replacement of EAG by other delayed rectifiers in diurnal insects. ABSTRACT The principles underlying evolutionary selection of ion channels for expression in sensory neurons are unclear. Among species possessing microvillar photoreceptors, the major ionic conductances have only been identified in Drosophila melanogaster. In Drosophila, depolarization is provided by light-activated transient receptor potential (TRP) channels with a minor contribution from TRP-like (TRPL) channels, whereas repolarization is mediated by sustained voltage-gated K+ (Kv) channels of the Shab family. Bright light stimulates Shab channels, further restricting depolarization and improving membrane bandwidth. In the present study, data obtained using a combination of electrophysiological, pharmacological and molecular knockdown techniques strongly suggest that in photoreceptors of the nocturnal cockroach Periplaneta americana the major excitatory channel is TRPL, whereas the predominant delayed rectifier is EAG, a ubiquitous but enigmatic Kv channel. By contrast to the diurnal Drosophila, bright light strongly suppresses EAG conductance in Periplaneta. This light-dependent inhibition (LDI) is caused by calcium entering the cytosol and is amplified following inhibition of calcium extrusion, and it can also be abolished by chelating intracellular calcium or suppressing eag gene expression by RNA interference. LDI increases membrane resistance, augments gain and reduces the signalling bandwidth, impairing information transfer. LDI is also observed in the nocturnal cricket Gryllus integer, whereas, in the diurnal water strider Gerris lacustris, the delayed rectifier is up-regulated by light. Although LDI is not expected to reduce delayed rectifier current in the normal illumination environment of nocturnal cockroaches and crickets, it makes EAG unsuitable for light response conditioning during the day, and might have resulted in the evolutionary replacement of EAG by other delayed rectifiers in diurnal insects.
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Affiliation(s)
- Esa-Ville Immonen
- Biophysics group, Nano and Molecular Systems Research Unit, University of Oulu, Oulu, Finland
| | - Andrew S French
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
| | - Päivi H Torkkeli
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
| | - Hongxia Liu
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
| | - Mikko Vähäsöyrinki
- Biophysics group, Nano and Molecular Systems Research Unit, University of Oulu, Oulu, Finland
| | - Roman V Frolov
- Biophysics group, Nano and Molecular Systems Research Unit, University of Oulu, Oulu, Finland
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3
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Kv10.1 K+ channel: from physiology to cancer. Pflugers Arch 2016; 468:751-62. [DOI: 10.1007/s00424-015-1784-3] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 12/11/2015] [Accepted: 12/27/2015] [Indexed: 12/18/2022]
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4
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Lin TF, Jow GM, Fang HY, Fu SJ, Wu HH, Chiu MM, Jeng CJ. The Eag domain regulates the voltage-dependent inactivation of rat Eag1 K+ channels. PLoS One 2014; 9:e110423. [PMID: 25333352 PMCID: PMC4204861 DOI: 10.1371/journal.pone.0110423] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Accepted: 09/14/2014] [Indexed: 01/29/2023] Open
Abstract
Eag (Kv10) and Erg (Kv11) belong to two distinct subfamilies of the ether-à-go-go K+ channel family (KCNH). While Erg channels are characterized by an inward-rectifying current-voltage relationship that results from a C-type inactivation, mammalian Eag channels display little or no voltage-dependent inactivation. Although the amino (N)-terminal region such as the eag domain is not required for the C-type inactivation of Erg channels, an N-terminal deletion in mouse Eag1 has been shown to produce a voltage-dependent inactivation. To further discern the role of the eag domain in the inactivation of Eag1 channels, we generated N-terminal chimeras between rat Eag (rEag1) and human Erg (hERG1) channels that involved swapping the eag domain alone or the complete cytoplasmic N-terminal region. Functional analyses indicated that introduction of the homologous hERG1 eag domain led to both a fast phase and a slow phase of channel inactivation in the rEag1 chimeras. By contrast, the inactivation features were retained in the reverse hERG1 chimeras. Furthermore, an eag domain-lacking rEag1 deletion mutant also showed the fast phase of inactivation that was notably attenuated upon co-expression with the rEag1 eag domain fragment, but not with the hERG1 eag domain fragment. Additionally, we have identified a point mutation in the S4-S5 linker region of rEag1 that resulted in a similar inactivation phenotype. Biophysical analyses of these mutant constructs suggested that the inactivation gating of rEag1 was distinctly different from that of hERG1. Overall, our findings are consistent with the notion that the eag domain plays a critical role in regulating the inactivation gating of rEag1. We propose that the eag domain may destabilize or mask an inherent voltage-dependent inactivation of rEag1 K+ channels.
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Affiliation(s)
- Ting-Feng Lin
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei, Taiwan
| | - Guey-Mei Jow
- School of Medicine, Fu-Jen Catholic University, Hsin-Chuang, New Taipei City, Taiwan
| | - Hsin-Yu Fang
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei, Taiwan
| | - Ssu-Ju Fu
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei, Taiwan
| | - Hao-Han Wu
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei, Taiwan
| | - Mei-Miao Chiu
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei, Taiwan
| | - Chung-Jiuan Jeng
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei, Taiwan
- Brain Research Center, National Yang-Ming University, Taipei, Taiwan
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5
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Srinivasan S, Lance K, Levine RB. Contribution of EAG to excitability and potassium currents in Drosophila larval motoneurons. J Neurophysiol 2012; 107:2660-71. [PMID: 22323637 DOI: 10.1152/jn.00201.2011] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Diversity in the expression of K(+) channels among neurons allows a wide range of excitability, growth, and functional regulation. Ether-à-go-go (EAG), a voltage-gated K(+) channel, was first characterized in Drosophila mutants by spontaneous firing in nerve terminals and enhanced neurotransmitter release. Although diverse functions have been ascribed to this protein, its role within neurons remains poorly understood. The aim of this study was to characterize the function of EAG in situ in Drosophila larval motoneurons. Whole cell patch-clamp recordings performed from the somata revealed a decrease in I(Av) and I(Kv) K(+) currents in eag mutants and with targeted eag RNAi expression. Spontaneous spike-like events were observed in eag mutants but absent in wild-type motoneurons. Thus our results provide evidence that EAG represents a unique K(+) channel contributing to multiple K(+) currents in motoneurons helping to regulate excitability, consistent with previous observations in the Drosophila larval muscle.
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6
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Preuss CP, Huang CY, Tyerman SD. Proton-coupled high-affinity phosphate transport revealed from heterologous characterization in Xenopus of barley-root plasma membrane transporter, HvPHT1;1. PLANT, CELL & ENVIRONMENT 2011; 34:681-9. [PMID: 21309796 DOI: 10.1111/j.1365-3040.2010.02272.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
High-affinity phosphate transporters mediate uptake of inorganic phosphate (P(i) ) from soil solution under low P(i) conditions. The electrophysiological properties of any plant high-affinity P(i) transporter have not been described yet. Here, we report the detailed characterization of electrophysiological properties of the barley P(i) transporter, HvPHT1;1 in Xenopus laevis oocytes. A very low K(m) value (1.9 µm) for phosphate transport was observed in HvPHT1;1, which falls within the concentration range observed for barley roots. Inward currents at negative membrane potentials were identified as nH+ :P(i)⁻ (n > 1) co-transport based on simultaneous P(i) radiotracer uptake, oocyte voltage clamping and pH dependence. HvPHT1;1 showed preferential selectivity for P(i) and arsenate, but no transport of the other oxyanions SO₄²⁻ and NO₃⁻. In addition, HvPHT1;1 locates to the plasma membrane when expressed in onion (Allium cepa L.) epidermal cells, and is highly expressed in root segments with dense hairs. The electrophysiological properties, plasma membrane localization and cell-specific expression pattern of HvPHT1;1 support its role in the uptake of P(i) under low P(i) conditions.
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Affiliation(s)
- Christian P Preuss
- School of Agriculture, Food and Wine, The University of Adelaide, South Australia, Australia
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7
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Sun XX, Bostrom SL, Griffith LC. Alternative splicing of the eag potassium channel gene in Drosophila generates a novel signal transduction scaffolding protein. Mol Cell Neurosci 2008; 40:338-43. [PMID: 19130887 DOI: 10.1016/j.mcn.2008.11.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2008] [Revised: 11/08/2008] [Accepted: 11/21/2008] [Indexed: 01/24/2023] Open
Abstract
The Drosophila eag gene has been shown to regulate neuronal excitability, olfaction, associative learning and larval locomotion. Not all of the roles of this gene in these processes can be explained by its function as a voltage-gated potassium channel. In this study, we show that the eag gene is spliced in a PKA- and PKC-regulated manner to produce a protein lacking channel domains. This protein, in the context of activated PKA, can engage cellular signaling pathways that alter cell structure. Nuclear localization is necessary for C-terminal-mediated effects, which also require MAPK. The requirement for PKA/PKC activation in the synthesis and function of this novel protein suggests that it may couple membrane events to nuclear signaling to regulate neuronal function on long time scales.
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Affiliation(s)
- Xiu Xia Sun
- Department of Biology, National Center for Behavioral Genomics, Brandeis University, Waltham, MA 02454-9110, USA
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8
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Pineda RH, Knoeckel CS, Taylor AD, Estrada-Bernal A, Ribera AB. Kv1 potassium channel complexes in vivo require Kvbeta2 subunits in dorsal spinal neurons. J Neurophysiol 2008; 100:2125-36. [PMID: 18684900 DOI: 10.1152/jn.90667.2008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Whereas Kvbeta2 subunits modulate potassium current properties carried by Kv1 channel complexes in heterologous systems, little is known about the contributions of Kvbeta2 subunits to native potassium channel function. Using antisense approaches and in situ recordings from Xenopus embryo spinal cord neurons, we tested the in vivo roles of Kvbeta2 subunits in modulation of voltage-dependent potassium current (IKv). We focused on 1) two different populations of dorsal spinal neurons that express both Kvbeta2 and Kv1 alpha-subunit genes and 2) the 24- and 48-h developmental period, during which IKv undergoes developmental regulation. At both 24 and 48 h, antisense methods produced efficient knock-down of both Kvbeta2 protein and IKv. At both times, dominant negative suppression of Kv1 channels also eliminated IKv, indicating that Kv1 channels require Kvbeta2 subunits to function in dorsal spinal neurons. Even though Kv1 channels determined the IKv values of both dorsal neuron types, comparisons of their IKv properties revealed important differences at both developmental stages. The latter results support the notion that different Kv1 alpha-subunits and/or posttranslational modifications underlie the IKv values of the two dorsal neuron types. Overall, the results demonstrate that Kvbeta2 subunits function in vivo as obligatory subunits of Kv1 channels in at least two neuron types and two different developmental stages.
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Affiliation(s)
- Ricardo H Pineda
- Department of Physiology and Biophysics MS8307, 12800 East 19th Avenue, University of Colorado Denver at AMC, Aurora, CO 80045, USA
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9
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Peng IF, Wu CF. Differential contributions of Shaker and Shab K+ currents to neuronal firing patterns in Drosophila. J Neurophysiol 2006; 97:780-94. [PMID: 17079336 DOI: 10.1152/jn.01012.2006] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Different K(+) currents participate in generating neuronal firing patterns. The Drosophila embryonic "giant" neuron culture system has facilitated current- and voltage-clamp recordings to correlate distinct excitability patterns with the underlying K(+) currents and to delineate the mutational effects of identified K(+) channels. Mutations of Sh and Shab K(+) channels removed part of inactivating I(A) and sustained I(K), respectively, and the remaining I(A) and I(K) revealed the properties of their counterparts, e.g., Shal and Shaw channels. Neuronal subsets displaying the delayed, tonic, adaptive, and damping spike patterns were characterized by different profiles of K(+) current voltage dependence and kinetics and by differential mutational effects. Shab channels regulated membrane repolarization and repetitive firing over hundreds of milliseconds, and Shab neurons showed a gradual decline in repolarization during current injection and their spike activities became limited to high-frequency, damping firing. In contrast, Sh channels acted on events within tens of milliseconds, and Sh mutations broadened spikes and reduced firing rates without eliminating any categories of firing patterns. However, removing both Sh and Shal I(A) by 4-aminopyridine converted the delayed to damping firing pattern, demonstrating their actions in regulating spike initiation. Specific blockade of Shab I(K) by quinidine mimicked the Shab phenotypes and converted tonic firing to a damping pattern. These conversions suggest a hierarchy of complexity in K(+) current interactions underlying different firing patterns. Different lineage-defined neuronal subsets, identifiable by employing the GAL4-UAS system, displayed different profiles of spike properties and K(+) current compositions, providing opportunities for mutational analysis in functionally specialized neurons.
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Affiliation(s)
- I-Feng Peng
- Department of Biological Sciences, University of Iowa, Iowa City, IA 52242, USA
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10
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Cardnell RJG, Nogare DED, Ganetzky B, Stern M. In vivo analysis of a gain-of-function mutation in the Drosophila eag-encoded K+ channel. Genetics 2006; 172:2351-8. [PMID: 16452147 PMCID: PMC1456403 DOI: 10.1534/genetics.105.048777] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Neuronal Na+ and K+ channels elicit currents in opposing directions and thus have opposing effects on neuronal excitability. Mutations in genes encoding Na+ or K+ channels often interact genetically, leading to either phenotypic suppression or enhancement for genes with opposing or similar effects on excitability, respectively. For example, the effects of mutations in Shaker (Sh), which encodes a K+ channel subunit, are suppressed by loss-of-function mutations in the Na+ channel structural gene para, but enhanced by loss-of-function mutations in a second K+ channel encoded by eag. Here we identify two novel mutations that suppress the effects of a Sh mutation on behavior and neuronal excitability. We used recombination mapping to localize both mutations to the eag locus, and we used sequence analysis to determine that both mutations are caused by a single amino acid substitution (G297E) in the S2-S3 linker of Eag. Because these novel eag mutations confer opposite phenotypes to eag loss-of-function mutations, we suggest that eag(G297E) causes an eag gain-of-function phenotype. We hypothesize that the G297E substitution may cause premature, prolonged, or constitutive opening of the Eag channels by favoring the "unlocked" state of the channel.
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Affiliation(s)
- Robert J G Cardnell
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77251-1892, USA.
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11
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Gordon E, Roepke TK, Abbott GW. Endogenous KCNE subunits govern Kv2.1 K+ channel activation kinetics in Xenopus oocyte studies. Biophys J 2005; 90:1223-31. [PMID: 16326911 PMCID: PMC1367273 DOI: 10.1529/biophysj.105.072504] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Kv2.1 is a voltage-gated potassium (Kv) channel that generates delayed rectifier currents in mammalian heart and brain. The biophysical properties of Kv2.1 and other ion channels have been characterized by functional expression in heterologous systems, and most commonly in Xenopus laevis oocytes. A number of previous oocyte-based studies of mammalian potassium channels have revealed expression-level-dependent changes in channel properties, leading to the suggestion that endogenous oocyte factors regulate channel gating. Here, we show that endogenous oocyte potassium channel KCNE ancillary subunits xMinK and xMiRP2 slow the activation of oocyte-expressed mammalian Kv2.1 channels two-to-fourfold. This produces a sigmoidal relationship between Kv2.1 current density and activation rate in oocyte-based two-electrode voltage clamp studies. The effect of endogenous xMiRP2 and xMinK on Kv2.1 activation is diluted at high Kv2.1 expression levels, or by RNAi knockdown of either endogenous subunit. RNAi knockdown of both xMiRP2 and xMinK eliminates the correlation between Kv2.1 expression level and activation kinetics. The data demonstrate a molecular basis for expression-level-dependent changes in Kv channel gating observed in heterologous expression studies.
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Affiliation(s)
- Earl Gordon
- Greenberg Division of Cardiology, Department of Medicine, Cornell University, Weill Medical College, New York 10021, USA
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12
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Keyser MR, Anson BD, Titus SA, Ganetzky B, Witten JL. Molecular characterization, functional expression, and developmental profile of an ether à-go-go K+ channel in the tobacco hornworm Manduca sexta. JOURNAL OF NEUROBIOLOGY 2003; 55:73-85. [PMID: 12605460 DOI: 10.1002/neu.10188] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
A very large number of evolutionarily conserved potassium channels have been identified but very little is known about their function or modulation in vivo. Metamorphosis of the tobacco hornworm, Manduca sexta, is a compelling model system for such studies because it permits analysis to be conducted at the level of identified neurons whose roles in simple behaviors and endocrine regulation are known. We present here the characterization of the first ion channel to be cloned from this animal. Partial genomic sequence for Manduca sexta ether à-go-go (Mseag) and a cDNA clone encoding the Mseag open reading frame were obtained. Genomic Southern analysis indicates that Manduca contains a single member of the eag subfamily per haploid genome. When expressed in Xenopus oocytes, MsEag channels conduct a voltage-dependent, K+ selective outward current with an inactivating component that closely resembles the Drosophila eag current. Mseag transcripts were restricted to the nervous system, adult antenna, and one set of larval skeletal muscles. Steroid hormonal regulation of Mseag expression is suggested by the temporal correlation of developmental changes in transcript expression with the changing steroid titers that promote metamorphosis. These results provide the foundation for functional and modulatory studies of the Eag family of K+ channels in Manduca, which will complement the genetic analysis in Drosophila.
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Affiliation(s)
- Matthew R Keyser
- Department of Biological Sciences, P.O. Box 413, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201, USA
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13
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Clyne JD, Brown TC, Hume RI. Expression level dependent changes in the properties of P2X2 receptors. Neuropharmacology 2003; 44:403-12. [PMID: 12604087 DOI: 10.1016/s0028-3908(02)00406-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The currents of P2X(2) receptors expressed in Xenopus oocytes or HEK293 cells show significant cell-to-cell variation in many properties including the rate of desensitization and the magnitude of potentiation by zinc or acidic pH. In this study, we examined whether differences in expression levels underlie this variability. We injected Xenopus oocytes with different concentrations of RNA encoding rat P2X(2) to give a wide range of maximum current amplitudes, and then measured the potentiation of responses to 10 micro M adenosine 5'-triphosphate (ATP) by zinc or acidic pH. Individual oocytes showed potentiation ratios that ranged from 1.4- to 25-fold. Oocytes with small amplitude responses to a saturating concentration of ATP tended to have larger potentiation ratios than oocytes with large amplitude responses. This phenomenon was explained by an inverse correlation between the EC(50) for ATP and the maximum current amplitude, with the EC(50) decreasing from about 37 to 7 micro M as expression level increased. In contrast, the Hill coefficient was not correlated with the maximum current amplitude. Truncated receptors lacking the last 76 amino acids also showed an inverse correlation between the EC(50) and the maximum current amplitude. Thus, the interactions that cause expression-dependent changes in P2X(2) receptor properties must involve domains proximal to position H397.
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Affiliation(s)
- J D Clyne
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, 3095 Natural Science Building, 830 N. University Avenue, Ann Arbor, MI 48109-1048, USA
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14
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Jenke M, Sánchez A, Monje F, Stühmer W, Weseloh RM, Pardo LA. C-terminal domains implicated in the functional surface expression of potassium channels. EMBO J 2003; 22:395-403. [PMID: 12554641 PMCID: PMC140720 DOI: 10.1093/emboj/cdg035] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
A short C-terminal domain is required for correct tetrameric assembly in some potassium channels. Here, we show that this domain forms a coiled coil that determines not only the stability but also the selectivity of the multimerization. Synthetic peptides comprising the sequence of this domain in Eag1 and other channels are able to form highly stable tetrameric coiled coils and display selective heteromultimeric interactions. We show that loss of function caused by disruption of this domain in Herg1 can be rescued by introducing the equivalent domain from Eag1, and that this chimeric protein can form heteromultimers with Eag1 while wild-type Erg1 cannot. Additionally, a short endoplasmic reticulum retention sequence closely preceding the coiled coil plays a crucial role for surface expression. Both domains appear to co-operate to form fully functional channels on the cell surface and are a frequent finding in ion channels. Many pathological phenotypes may be attributed to mutations affecting one or both domains.
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Affiliation(s)
- Marc Jenke
- Max Planck Institute for Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
Present address: iOnGen AG, Rudolf Wissell Straße 28, 37079 Göttingen, Germany Present address: Oppenheim Research GmbH, Unter Sachsenlausen 4, 50667 Köln, Germany Corresponding author e-mail:
R.M.Weseloh and L.A.Pardo contributed equally to this work
| | | | | | | | - Rüdiger M. Weseloh
- Max Planck Institute for Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
Present address: iOnGen AG, Rudolf Wissell Straße 28, 37079 Göttingen, Germany Present address: Oppenheim Research GmbH, Unter Sachsenlausen 4, 50667 Köln, Germany Corresponding author e-mail:
R.M.Weseloh and L.A.Pardo contributed equally to this work
| | - Luis A. Pardo
- Max Planck Institute for Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
Present address: iOnGen AG, Rudolf Wissell Straße 28, 37079 Göttingen, Germany Present address: Oppenheim Research GmbH, Unter Sachsenlausen 4, 50667 Köln, Germany Corresponding author e-mail:
R.M.Weseloh and L.A.Pardo contributed equally to this work
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15
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Lazaroff MA, Taylor AD, Ribera AB. In vivo analysis of Kvbeta2 function in Xenopus embryonic myocytes. J Physiol 2002; 541:673-83. [PMID: 12068032 PMCID: PMC2290371 DOI: 10.1113/jphysiol.2002.016568] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2002] [Accepted: 03/19/2002] [Indexed: 11/08/2022] Open
Abstract
Kv1 potassium channels consist of pore-forming alpha subunits as well as auxiliary beta subunits. In heterologous systems, Kv1alpha subunits suffice for induction of voltage-dependent potassium current (I(Kv)). Although Kv1 channels can be expressed without auxiliary subunits in heterologous systems, coexpression with Kvbeta subunits has dramatic effects on surface expression and kinetic properties. Much less is known about the functional roles of Kvbeta subunits in vivo, despite their presence in the majority of native Kv1 channel complexes. We used an antisense approach to probe the contribution of Kvbeta2 subunits to native Kv1 channel function in embryonic myocytes. We compared the effects of antisense Kvbeta2 treatment on the whole cell I(Kv) to those produced by overexpression of a dominant-negative Kv1alpha subunit. The reductions in the maximal potassium conductance produced by antisense Kvbeta2 treatment and elimination of Kv1alpha subunit function were not significantly different from each other. In addition, simultaneous elimination of Kv1alpha and Kvbeta2 subunit function resulted in no further reduction of the maximal conductance. The Kv channel complexes targeted by Kvbeta2 and/or Kv1alpha subunit elimination contributed to action potential repolarization because elimination of either or both subunits led to increases in the duration of the action potential. As for potassium conductance, the effects of elimination of both alpha and beta subunits on the duration of the action potential were not additive. Taken together, the results suggest that Kv1 potassium channel complexes in vivo have a strong requirement for both alpha and beta subunits.
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Affiliation(s)
- Meredith A Lazaroff
- Department of Physiology and Biophysics C-240, University of Colorado Health Sciences Center, Denver 80262, USA
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McCormack K, Connor JX, Zhou L, Ho LL, Ganetzky B, Chiu SY, Messing A. Genetic analysis of the mammalian K+ channel beta subunit Kvbeta 2 (Kcnab2). J Biol Chem 2002; 277:13219-28. [PMID: 11825900 DOI: 10.1074/jbc.m111465200] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Kvbeta2 binds to K(+) channel alpha subunits from at least two different families (Kv1 and Kv4) and is a member of the aldo-ketoreductase (AKR) superfamily. Proposed functions for this protein in vivo include a chaperone-like role in Kv1 alpha subunit biogenesis and catalytic activity as an AKR oxidoreductase. To investigate the in vivo function of Kvbeta2, Kvbeta2-null and point mutant (Y90F) mice were generated through gene targeting in embryonic stem cells. In Kvbeta2-null mice, Kv1.1 and Kv1.2 localize normally in cerebellar basket cell terminals and the juxtaparanodal region of myelinated nerves. Moreover, normal glycosylation patterns are observed for Kv1.1 and Kv1.2 in whole brain lysates. Thus, loss of the chaperone-like activity does not appear to account for the phenotype of Kvbeta2-null mice, which include reduced life spans, occasional seizures, and cold swim-induced tremors similar to that observed in Kv1.1-null mice. Mice expressing Kvbeta2, mutated at a site (Y90F) that abolishes AKR-like catalytic activity in other family members, have no overt phenotype. We conclude that Kvbeta2 contributes to regulation of excitability in vivo, although not directly through either chaperone-like or typical AKR catalytic activity. Rather, Kvbeta2 relies upon as yet unidentified mechanisms in the regulation of K(+) channel and/or oxidoreductive functions.
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Affiliation(s)
- Ken McCormack
- Department of Pathobiological Sciences, Waisman Center, University of Wisconsin, Madison, WI 53705-2280, USA.
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17
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Ling KY, Haynes WJ, Oesterle L, Kung C, Preston RR, Saimi Y. K(+)-channel transgenes reduce K(+) currents in Paramecium, probably by a post-translational mechanism. Genetics 2001; 159:987-95. [PMID: 11729147 PMCID: PMC1461881 DOI: 10.1093/genetics/159.3.987] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
PAK11 is 1 of more than 15 members in a gene family that encodes K(+)-channel pore-forming subunits in Paramecium tetraurelia. Microinjection of PAK11 DNA into macronuclei of wild-type cells results in clonal transformants that exhibit hyperexcitable swimming behaviors reminiscent of certain loss-of-K(+)-current mutants. PAK2, a distant homolog of PAK11, does not have the same effect. But PAK1, a close homolog of PAK11, induces the same hyperexcitability. Cutting the PAK11 open reading frame (ORF) with restriction enzymes before injection removes this effect entirely. Microinjection of PAK11 ORF flanked by the calmodulin 5' and 3' UTRs also induces the same hyperexcitable phenotype. Direct examination of transformed cells under voltage clamp reveals that two different Ca(2+)-activated K(+)-specific currents are reduced in amplitude. This reduction does not correlate with a deficit of PAK11 message, since RNA is clearly produced from the injected transgenes. Insertion of a single nucleotide at the start of the PAK11 ORF does not affect the RNA level but completely abolishes the phenotypic transformation. Thus, the reduction of K(+) currents by the expression of the K(+)-channel transgenes reported here is likely to be the consequence of a post-translational event. The complexity of behavioral changes, possible mechanisms, and implications in Paramecium biology are discussed.
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Affiliation(s)
- K Y Ling
- Laboratory of Molecular Biology and Department of Genetics, University of Wisconsin, Madison, Wisconsin 53706, USA
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18
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A novel leg-shaking Drosophila mutant defective in a voltage-gated K(+)current and hypersensitive to reactive oxygen species. J Neurosci 2000. [PMID: 10934243 DOI: 10.1523/jneurosci.20-16-05958.2000] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
1,1'-Dimethyl-4,4'-bipyridinium dichloride (methyl viologen; paraquat), an herbicide that causes depletion of NADPH and generates excessive reactive oxygen species (ROS) in vivo, has been used to screen for ROS-sensitive Drosophila mutants. One mutant so isolated, named quiver(1) (qvr(1)), has a leg-shaking phenotype. Mutants of the Shaker (Sh), Hyperkinetic (Hk), and ether a go-go (eag) genes, which encode different K(+) channel subunits that regulate the A-type K(+) current (I(A)) in different ways, exhibit leg shaking under ether anesthesia and have heightened metabolic rates and shortened life spans. We found that Sh, Hk, and eag mutant flies were all hypersensitive to paraquat. Double-mutant combinations among the three channel mutations and qvr(1) had drastically enhanced sensitivity to paraquat. Synaptic transmission at the larval neuromuscular junction was increased in the qvr(1) mutant to the level of Sh mutants. Similar to eag Sh double mutants, double mutants of eag and qvr(1) showed striking enhancement in synaptic transmission and a wings-down phenotype, the hallmarks of extreme hyperexcitability. Voltage-clamp experiments demonstrated that the qvr(1) mutation specifically disrupted the Sh-dependent I(A) current without altering the other currents [I(K), Ca(2+)-activated fast (I(CF)) and slow (I(CS)) currents, and I(Ca)] in larval muscles. Several deficiency strains of the qvr locus failed to complement qvr(1) and confirmed that ether-induced leg shaking, reduced I(A) current, and paraquat hypersensitivity map to the same locus. Our results suggest that the qvr gene may encode a novel K(+) channel-related polypeptide and indicate a strong link between a voltage-activated K(+) current and vulnerability to ROS.
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Wang JW, Humphreys JM, Phillips JP, Hilliker AJ, Wu CF. A novel leg-shaking Drosophila mutant defective in a voltage-gated K(+)current and hypersensitive to reactive oxygen species. J Neurosci 2000; 20:5958-64. [PMID: 10934243 PMCID: PMC6772572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2000] [Revised: 05/22/2000] [Accepted: 06/01/2000] [Indexed: 02/17/2023] Open
Abstract
1,1'-Dimethyl-4,4'-bipyridinium dichloride (methyl viologen; paraquat), an herbicide that causes depletion of NADPH and generates excessive reactive oxygen species (ROS) in vivo, has been used to screen for ROS-sensitive Drosophila mutants. One mutant so isolated, named quiver(1) (qvr(1)), has a leg-shaking phenotype. Mutants of the Shaker (Sh), Hyperkinetic (Hk), and ether a go-go (eag) genes, which encode different K(+) channel subunits that regulate the A-type K(+) current (I(A)) in different ways, exhibit leg shaking under ether anesthesia and have heightened metabolic rates and shortened life spans. We found that Sh, Hk, and eag mutant flies were all hypersensitive to paraquat. Double-mutant combinations among the three channel mutations and qvr(1) had drastically enhanced sensitivity to paraquat. Synaptic transmission at the larval neuromuscular junction was increased in the qvr(1) mutant to the level of Sh mutants. Similar to eag Sh double mutants, double mutants of eag and qvr(1) showed striking enhancement in synaptic transmission and a wings-down phenotype, the hallmarks of extreme hyperexcitability. Voltage-clamp experiments demonstrated that the qvr(1) mutation specifically disrupted the Sh-dependent I(A) current without altering the other currents [I(K), Ca(2+)-activated fast (I(CF)) and slow (I(CS)) currents, and I(Ca)] in larval muscles. Several deficiency strains of the qvr locus failed to complement qvr(1) and confirmed that ether-induced leg shaking, reduced I(A) current, and paraquat hypersensitivity map to the same locus. Our results suggest that the qvr gene may encode a novel K(+) channel-related polypeptide and indicate a strong link between a voltage-activated K(+) current and vulnerability to ROS.
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Affiliation(s)
- J W Wang
- Department of Biological Sciences, University of Iowa, Iowa City, Iowa 52242, USA
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