51
|
DiFranco M, Quinonez M, Vergara JL. The delayed rectifier potassium conductance in the sarcolemma and the transverse tubular system membranes of mammalian skeletal muscle fibers. ACTA ACUST UNITED AC 2012; 140:109-37. [PMID: 22851675 PMCID: PMC3409102 DOI: 10.1085/jgp.201210802] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
A two-microelectrode voltage clamp and optical measurements of membrane potential changes at the transverse tubular system (TTS) were used to characterize delayed rectifier K currents (IK(V)) in murine muscle fibers stained with the potentiometric dye di-8-ANEPPS. In intact fibers, IK(V) displays the canonical hallmarks of K(V) channels: voltage-dependent delayed activation and decay in time. The voltage dependence of the peak conductance (gK(V)) was only accounted for by double Boltzmann fits, suggesting at least two channel contributions to IK(V). Osmotically treated fibers showed significant disconnection of the TTS and displayed smaller IK(V), but with similar voltage dependence and time decays to intact fibers. This suggests that inactivation may be responsible for most of the decay in IK(V) records. A two-channel model that faithfully simulates IK(V) records in osmotically treated fibers comprises a low threshold and steeply voltage-dependent channel (channel A), which contributes ∼31% of gK(V), and a more abundant high threshold channel (channel B), with shallower voltage dependence. Significant expression of the IK(V)1.4 and IK(V)3.4 channels was demonstrated by immunoblotting. Rectangular depolarizing pulses elicited step-like di-8-ANEPPS transients in intact fibers rendered electrically passive. In contrast, activation of IK(V) resulted in time- and voltage-dependent attenuations in optical transients that coincided in time with the peaks of IK(V) records. Normalized peak attenuations showed the same voltage dependence as peak IK(V) plots. A radial cable model including channels A and B and K diffusion in the TTS was used to simulate IK(V) and average TTS voltage changes. Model predictions and experimental data were compared to determine what fraction of gK(V) in the TTS accounted simultaneously for the electrical and optical data. Best predictions suggest that K(V) channels are approximately equally distributed in the sarcolemma and TTS membranes; under these conditions, >70% of IK(V) arises from the TTS.
Collapse
Affiliation(s)
- Marino DiFranco
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | | | | |
Collapse
|
52
|
Kleopa KA. Autoimmune channelopathies of the nervous system. Curr Neuropharmacol 2012; 9:458-67. [PMID: 22379460 PMCID: PMC3151600 DOI: 10.2174/157015911796557966] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2010] [Revised: 03/16/2010] [Accepted: 03/16/2010] [Indexed: 12/20/2022] Open
Abstract
Ion channels are complex transmembrane proteins that orchestrate the electrical signals necessary for normal function of excitable tissues, including the central nervous system, peripheral nerve, and both skeletal and cardiac muscle. Progress in molecular biology has allowed cloning and expression of genes that encode channel proteins, while comparable advances in biophysics, including patch-clamp electrophysiology and related techniques, have made the functional assessment of expressed proteins at the level of single channel molecules possible. The role of ion channel defects in the pathogenesis of numerous disorders has become increasingly apparent over the last two decades. Neurological channelopathies are frequently genetically determined but may also be acquired through autoimmune mechanisms. All of these autoimmune conditions can arise as paraneoplastic syndromes or independent from malignancies. The pathogenicity of autoantibodies to ion channels has been demonstrated in most of these conditions, and patients may respond well to immunotherapies that reduce the levels of the pathogenic autoantibodies. Autoimmune channelopathies may have a good prognosis, especially if diagnosed and treated early, and if they are non-paraneoplastic. This review focuses on clinical, pathophysiologic and therapeutic aspects of autoimmune ion channel disorders of the nervous system.
Collapse
Affiliation(s)
- Kleopas A Kleopa
- Neurology Clinics and Neuroscience Laboratory, The Cyprus Institute of Neurology and Genetics, Cyprus
| |
Collapse
|
53
|
Kanda VA, Abbott GW. KCNE Regulation of K(+) Channel Trafficking - a Sisyphean Task? Front Physiol 2012; 3:231. [PMID: 22754540 PMCID: PMC3385356 DOI: 10.3389/fphys.2012.00231] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Accepted: 06/08/2012] [Indexed: 11/16/2022] Open
Abstract
Voltage-gated potassium (Kv) channels shape the action potentials of excitable cells and regulate membrane potential and ion homeostasis in excitable and non-excitable cells. With 40 known members in the human genome and a variety of homomeric and heteromeric pore-forming α subunit interactions, post-translational modifications, cellular locations, and expression patterns, the functional repertoire of the Kv α subunit family is monumental. This versatility is amplified by a host of interacting proteins, including the single membrane-spanning KCNE ancillary subunits. Here, examining both the secretory and the endocytic pathways, we review recent findings illustrating the surprising virtuosity of the KCNE proteins in orchestrating not just the function, but also the composition, diaspora and retrieval of channels formed by their Kv α subunit partners.
Collapse
Affiliation(s)
- Vikram A Kanda
- Department of Biology, Manhattan College Riverdale, New York, NY, USA
| | | |
Collapse
|
54
|
A genome-wide association study identifies novel susceptibility genetic variation for thyrotoxic hypokalemic periodic paralysis. J Hum Genet 2012; 57:301-4. [PMID: 22399142 DOI: 10.1038/jhg.2012.20] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Several lines of evidence have pointed out that genetic components have roles in thyrotoxic hypokalemic periodic paralysis (TTPP). In this study, for the first time we performed genome-wide association study (GWAS) in male hyperthyroid subjects in order to identify genetic loci conferring susceptibility to TTPP. We genotyped 78 Thai male TTPP cases and 74 Thai male hyperthyroid patients without hypokalemia as controls with Illumina Human-Hap610 Genotyping BeadChip. Among the SNPs analyzed in the GWAS, rs312729 at chromosome 17q revealed the lowest P-value for association (P=2.09 × 10(-7)). After fine mapping for linkage disequilibrium blocks surrounding the landmark SNP, we found a significant association of rs623011; located at 75 kb downstream of KCNJ2 on chromosome 17q, reached the GWAS significance after Bonferroni's adjustment (P=3.23 × 10(-8), odds ratio (OR)=6.72; 95% confidence interval (CI)=3.11-14.5). The result was confirmed in an independent cohort of samples consisting of 28 TTPP patients and 48 controls using the same clinical criteria diagnosis (replication analysis P=3.44 × 10(-5), OR=5.13; 95% CI=1.87-14.1; combined-analysis P=3.71 × 10(-12), OR=5.47; 95% CI=3.04-9.83).
Collapse
|
55
|
Roura-Ferrer M, Solé L, Oliveras A, Villarroel A, Comes N, Felipe A. Targeting of Kv7.5 (KCNQ5)/KCNE channels to surface microdomains of cell membranes. Muscle Nerve 2012; 45:48-54. [PMID: 22190306 DOI: 10.1002/mus.22231] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
BACKGROUND Kv7.5 (KCNQ5) channels conduct M-type potassium currents in the brain, are expressed in skeletal muscle, and contribute to vascular muscle tone. METHODS We coexpressed Kv7.5 and KCNE1-3 peptides in HEK293 cells and then analyzed their association using electrophysiology and co-immunoprecipitation, assessed localization using confocal microscopy, examined targeting of the oligomeric channels to cholesterol-rich membrane surface microdomains using lipid raft isolation, and evaluated their membrane dynamics using fluorescence recovery after photobleaching (FRAP). RESULTS Kv7.5 forms oligomeric channels specifically with KCNE1 and KCNE3. The expression of Kv7.5 targeted to cholesterol-rich membrane surface microdomains was very low. Oligomeric Kv7.5/KCNE1 and Kv7.5/KCNE3 channels did not localize to lipid rafts. However, Kv7.5 association impaired KCNE3 expression in lipid raft microdomains. CONCLUSIONS Our results indicate that Kv7.5 contributes to the spatial regulation of KCNE3. This new scenario could greatly assist in determining the physiological relevance of putative KCNE3 interactions in nerve and muscle.
Collapse
Affiliation(s)
- Meritxell Roura-Ferrer
- Molecular Physiology Laboratory, Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina, Universitat de Barcelona, Avenida Diagonal 645, E-08028 Barcelona, Spain
| | | | | | | | | | | |
Collapse
|
56
|
Peltola MA, Kuja-Panula J, Lauri SE, Taira T, Rauvala H. AMIGO is an auxiliary subunit of the Kv2.1 potassium channel. EMBO Rep 2011; 12:1293-9. [PMID: 22056818 DOI: 10.1038/embor.2011.204] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2011] [Revised: 09/21/2011] [Accepted: 09/22/2011] [Indexed: 11/09/2022] Open
Abstract
Kv2.1 is a potassium channel α-subunit abundantly expressed throughout the brain. It is a main component of delayed rectifier current (I(K)) in several neuronal types and a regulator of excitability during high-frequency firing. Here we identify AMIGO (amphoterin-induced gene and ORF), a neuronal adhesion protein with leucine-rich repeat and immunoglobin domains, as an integral part of the Kv2.1 channel complex. AMIGO shows extensive spatial and temporal colocalization and association with Kv2.1 in the mouse brain. The colocalization of AMIGO and Kv2.1 is retained even during stimulus-induced changes in Kv2.1 localization. AMIGO increases Kv2.1 conductance in a voltage-dependent manner in HEK cells. Accordingly, inhibition of endogenous AMIGO suppresses neuronal I(K) at negative membrane voltages. In conclusion, our data indicate AMIGO as a function-modulating auxiliary subunit for Kv2.1 and thus provide new insights into regulation of neuronal excitability.
Collapse
Affiliation(s)
- Marjaana A Peltola
- Neuroscience Center, University of Helsinki, PO Box 56, Helsinki FI-00014, Finland.
| | | | | | | | | |
Collapse
|
57
|
The KCNE genes in hypertrophic cardiomyopathy: a candidate gene study. J Negat Results Biomed 2011; 10:12. [PMID: 21967835 PMCID: PMC3204304 DOI: 10.1186/1477-5751-10-12] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2011] [Accepted: 10/03/2011] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND The gene family KCNE1-5, which encode modulating β-subunits of several repolarising K+-ion channels, has been associated with genetic cardiac diseases such as long QT syndrome, atrial fibrillation and Brugada syndrome. The minK peptide, encoded by KCNE1, is attached to the Z-disc of the sarcomere as well as the T-tubules of the sarcolemma. It has been suggested that minK forms part of an "electro-mechanical feed-back" which links cardiomyocyte stretching to changes in ion channel function. We examined whether mutations in KCNE genes were associated with hypertrophic cardiomyopathy (HCM), a genetic disease associated with an improper hypertrophic response. RESULTS The coding regions of KCNE1, KCNE2, KCNE3, KCNE4, and KCNE5 were examined, by direct DNA sequencing, in a cohort of 93 unrelated HCM probands and 188 blood donor controls.Fifteen genetic variants, four previously unknown, were identified in the HCM probands. Eight variants were non-synonymous and one was located in the 3'UTR-region of KCNE4. No disease-causing mutations were found and no significant difference in the frequency of genetic variants was found between HCM probands and controls. Two variants of likely functional significance were found in controls only. CONCLUSIONS Mutations in KCNE genes are not a common cause of HCM and polymorphisms in these genes do not seem to be associated with a propensity to develop arrhythmia.
Collapse
|
58
|
Soldovieri MV, Miceli F, Taglialatela M. Driving With No Brakes: Molecular Pathophysiology of Kv7 Potassium Channels. Physiology (Bethesda) 2011; 26:365-76. [DOI: 10.1152/physiol.00009.2011] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Kv7 potassium channels regulate excitability in neuronal, sensory, and muscular cells. Here, we describe their molecular architecture, physiological roles, and involvement in genetically determined channelopathies highlighting their relevance as targets for pharmacological treatment of several human disorders.
Collapse
Affiliation(s)
| | - Francesco Miceli
- Department of Neuroscience, University of Naples Federico II, Naples; and
- Division of Neurology, IRCCS Bambino Gesù Children's Hospital, Rome, Italy
| | - Maurizio Taglialatela
- Department of Health Science, University of Molise, Campobasso
- Department of Neuroscience, University of Naples Federico II, Naples; and
| |
Collapse
|
59
|
Kanda VA, Lewis A, Xu X, Abbott GW. KCNE1 and KCNE2 provide a checkpoint governing voltage-gated potassium channel α-subunit composition. Biophys J 2011; 101:1364-75. [PMID: 21943417 DOI: 10.1016/j.bpj.2011.08.014] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Revised: 07/25/2011] [Accepted: 08/05/2011] [Indexed: 11/28/2022] Open
Abstract
Voltage-gated potassium (Kv) currents generated by N-type α-subunit homotetramers inactivate rapidly because an N-terminal ball domain blocks the channel pore after activation. Hence, the inactivation rate of heterotetrameric channels comprising both N-type and non-N-type (delayed rectifier) α-subunits depends upon the number of N-type α-subunits in the complex. As Kv channel inactivation and inactivation recovery rates regulate cellular excitability, the composition and expression of these heterotetrameric complexes are expected to be tightly regulated. In a companion article, we showed that the single transmembrane segment ancillary (β) subunits KCNE1 and KCNE2 suppress currents generated by homomeric Kv1.4, Kv3.3, and Kv3.4 channels, by trapping them early in the secretory pathway. Here, we show that this trapping is prevented by coassembly of the N-type α-subunits with intra-subfamily delayed rectifier α-subunits. Extra-subfamily delayed rectifier α-subunits, regardless of their capacity to interact with KCNE1 and KCNE2, cannot rescue Kv1.4 or Kv3.4 surface expression unless engineered to interact with them using N-terminal A and B domain swapping. The KCNE1/2-enforced checkpoint ensures N-type α-subunits only reach the cell surface as part of intra-subfamily mixed-α complexes, thereby governing channel composition, inactivation rate, and-by extension-cellular excitability.
Collapse
Affiliation(s)
- Vikram A Kanda
- Department of Pharmacology, Weill Medical College of Cornell University, New York, New York, USA
| | | | | | | |
Collapse
|
60
|
Kanda VA, Lewis A, Xu X, Abbott GW. KCNE1 and KCNE2 inhibit forward trafficking of homomeric N-type voltage-gated potassium channels. Biophys J 2011; 101:1354-63. [PMID: 21943416 DOI: 10.1016/j.bpj.2011.08.015] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Revised: 07/25/2011] [Accepted: 08/04/2011] [Indexed: 11/18/2022] Open
Abstract
Potassium currents generated by voltage-gated potassium (Kv) channels comprising α-subunits from the Kv1, 2, and 3 subfamilies facilitate high-frequency firing of mammalian neurons. Within these subfamilies, only three α-subunits (Kv1.4, Kv3.3, and Kv3.4) generate currents that decay rapidly in the open state because an N-terminal ball domain blocks the channel pore after activation-a process termed N-type inactivation. Despite its importance to shaping cellular excitability, little is known of the processes regulating surface expression of N-type α-subunits, versus their slowly inactivating (delayed rectifier) counterparts. Here we found that currents generated by homomeric Kv1.4, Kv3.3, and Kv3.4 channels are all strongly suppressed by the single transmembrane domain ancillary (β) subunits KCNE1 and KCNE2. A combination of electrophysiological, biochemical, and immunofluorescence analyses revealed this suppression is due to KCNE1 and KCNE2 retaining Kv1.4 and Kv3.4 intracellularly, early in the secretory pathway. The retention is specific, requires α-β coassembly, and does not involve the dynamin-dependent endocytosis pathway. However, the small fraction of Kv3.4 that escapes KCNE-dependent retention is regulated by dynamin-dependent endocytosis. The findings illustrate two contrasting mechanisms controlling surface expression of N-type Kv α-subunits and therefore, potentially, cellular excitability and refractory periods.
Collapse
Affiliation(s)
- Vikram A Kanda
- Department of Pharmacology, Weill Medical College of Cornell University, New York, New York, USA
| | | | | | | |
Collapse
|
61
|
Sand PG, Langguth B, Kleinjung T. Deep resequencing of the voltage-gated potassium channel subunit KCNE3 gene in chronic tinnitus. Behav Brain Funct 2011; 7:39. [PMID: 21899751 PMCID: PMC3180252 DOI: 10.1186/1744-9081-7-39] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2011] [Accepted: 09/07/2011] [Indexed: 11/24/2022] Open
Abstract
Membrane-stabilizing drugs have long been used for the treatment of chronic tinnitus, suggesting an underlying disturbance of sensory excitability due to changes in ion conductance. The present study addresses the potassium channel subunit gene KCNE3 as a potential candidate for tinnitus susceptibility. 288 Caucasian outpatients with a diagnosis of chronic tinnitus were systematically screened for mutations in the KCNE3 open reading frame and in the adjacent region by direct sequencing. Allele frequencies were determined for 11 known variants of which two (F66F and R83H) were polymorphic but were not associated with the disorder. No novel variants were identified and only three carriers of R83H were noted. However, owing to a lack of power, our study can neither rule out effects of KCNE3 on the risk for developing chronic tinnitus, nor can it exclude a role in predicting the severity of tinnitus. More extensive investigations are invited, including tests for possible effects of variation in this ion channel protein on the response to treatment.
Collapse
Affiliation(s)
- Philipp G Sand
- Department of Otorhinolaryngology, University of Regensburg, Franz-Josef-Strauss-Allee 11, Regensburg, Germany
| | | | | |
Collapse
|
62
|
Plant LD, Dowdell EJ, Dementieva IS, Marks JD, Goldstein SAN. SUMO modification of cell surface Kv2.1 potassium channels regulates the activity of rat hippocampal neurons. ACTA ACUST UNITED AC 2011; 137:441-54. [PMID: 21518833 PMCID: PMC3082930 DOI: 10.1085/jgp.201110604] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Voltage-gated Kv2.1 potassium channels are important in the brain for determining activity-dependent excitability. Small ubiquitin-like modifier proteins (SUMOs) regulate function through reversible, enzyme-mediated conjugation to target lysine(s). Here, sumoylation of Kv2.1 in hippocampal neurons is shown to regulate firing by shifting the half-maximal activation voltage (V1/2) of channels up to 35 mV. Native SUMO and Kv2.1 are shown to interact within and outside channel clusters at the neuronal surface. Studies of single, heterologously expressed Kv2.1 channels show that only K470 is sumoylated. The channels have four subunits, but no more than two non-adjacent subunits carry SUMO concurrently. SUMO on one site shifts V1/2 by 15 mV, whereas sumoylation of two sites produces a full response. Thus, the SUMO pathway regulates neuronal excitability via Kv2.1 in a direct and graded manner.
Collapse
Affiliation(s)
- Leigh D Plant
- Department of Pediatrics and Institute for Molecular Pediatric Sciences, Biological Sciences Division, Pritzker School of Medicine, University of Chicago, Chicago, IL 60637, USA
| | | | | | | | | |
Collapse
|
63
|
Li FF, Li QQ, Tan ZX, Zhang SY, Liu J, Zhao EY, Yu GC, Zhou J, Zhang LM, Liu SL. A Novel Mutation in CACNA1S Gene Associated with Hypokalemic Periodic Paralysis Which has a Gender Difference in the Penetrance. J Mol Neurosci 2011; 46:378-83. [DOI: 10.1007/s12031-011-9596-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Accepted: 07/11/2011] [Indexed: 10/17/2022]
|
64
|
Lewis AS, Estep CM, Chetkovich DM. The fast and slow ups and downs of HCN channel regulation. Channels (Austin) 2011; 4:215-31. [PMID: 20305382 DOI: 10.4161/chan.4.3.11630] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels (h channels) form the molecular basis for the hyperpolarization-activated current, I(h), and modulation of h channels contributes to changes in cellular properties critical for normal functions in the mammalian brain and heart. Numerous mechanisms underlie h channel modulation during both physiological and pathological conditions, leading to distinct changes in gating, kinetics, surface expression, channel conductance or subunit composition of h channels. Here we provide a focused review examining mechanisms of h channel regulation, with an emphasis on recent findings regarding interacting proteins such as TRIP8b. This review is intended to serve as a comprehensive resource for physiologists to provide potential molecular mechanisms underlying functionally important changes in I(h) in different biological models, as well as for molecular biologists to delineate the predicted h channel changes associated with complex regulatory mechanisms in both normal function and in disease states.
Collapse
Affiliation(s)
- Alan S Lewis
- Davee Department of Neurology and Clinical Neurosciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | | | | |
Collapse
|
65
|
McCallum LA, Pierce SL, England SK, Greenwood IA, Tribe RM. The contribution of Kv7 channels to pregnant mouse and human myometrial contractility. J Cell Mol Med 2011; 15:577-86. [PMID: 20132415 PMCID: PMC3922379 DOI: 10.1111/j.1582-4934.2010.01021.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Premature birth accounts for approximately 75% of neonatal mortality and morbidity in the developed world. Despite this, methods for identifying and treating women at risk of preterm labour are limited and many women still present in preterm labour requiring tocolytic therapy to suppress uterine contractility. The aim of this study was to assess the utility of Kv7 channel activators as potential uterine smooth muscle (myometrium) relaxants in tissues from pregnant mice and women. Myometrium was obtained from early and late pregnant mice and from lipopolysaccharide (LPS)-injected mice (day 15 of gestation; model of infection in pregnancy). Human myometrium was obtained at the time of Caesarean section from women at term (38–41 weeks). RT-PCR/qRT-PCR detected KCNQ and KCNE expression in mouse and human myometrium. In mice, there was a global suppression of all KCNQ isoforms, except KCNQ3, in early pregnancy (n= 6, P < 0.001 versus late pregnant); expression subsequently increased in late pregnancy (n= 6). KCNE isoforms were also gestationally regulated (P < 0.05). KCNQ and KCNE isoform expression was slightly down-regulated in myometrium from LPS-treated-mice versus controls (P < 0.05, n= 3–4). XE991 (10 μM, Kv7 inhibitor) significantly increased spontaneous myometrial contractions in vitro in both human and mouse myometrial tissues (P < 0.05) and retigabine/flupirtine (20 μM, Kv7 channel activators) caused profound myometrial relaxation (P < 0.05). In summary, Kv7 activators suppressed myometrial contraction and KCNQ gene expression was sustained throughout gestation, particularly at term. Consequently, activation of the encoded channels represents a novel mechanism for treatment of preterm labour.
Collapse
Affiliation(s)
- Laura A McCallum
- Maternal and Fetal Research Unit, Division of Reproduction and Endocrinology, King's College London, St Thomas' Hospital Campus, London, UK
| | | | | | | | | |
Collapse
|
66
|
KCNE1 enhances phosphatidylinositol 4,5-bisphosphate (PIP2) sensitivity of IKs to modulate channel activity. Proc Natl Acad Sci U S A 2011; 108:9095-100. [PMID: 21576493 DOI: 10.1073/pnas.1100872108] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Phosphatidylinositol 4,5-bisphosphate (PIP(2)) is necessary for the function of various ion channels. The potassium channel, I(Ks), is important for cardiac repolarization and requires PIP(2) to activate. Here we show that the auxiliary subunit of I(Ks), KCNE1, increases PIP(2) sensitivity 100-fold over channels formed by the pore-forming KCNQ1 subunits alone, which effectively amplifies current because native PIP(2) levels in the membrane are insufficient to activate all KCNQ1 channels. A juxtamembranous site in the KCNE1 C terminus is a key structural determinant of PIP(2) sensitivity. Long QT syndrome associated mutations of this site lower PIP(2) affinity, resulting in reduced current. Application of exogenous PIP(2) to these mutants restores wild-type channel activity. These results reveal a vital role of PIP(2) for KCNE1 modulation of I(Ks) channels that may represent a common mechanism of auxiliary subunit modulation of many ion channels.
Collapse
|
67
|
Maciel RMB, Lindsey SC, Dias da Silva MR. Novel etiopathophysiological aspects of thyrotoxic periodic paralysis. Nat Rev Endocrinol 2011; 7:657-67. [PMID: 21556020 DOI: 10.1038/nrendo.2011.58] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Thyrotoxicosis can lead to thyrotoxic periodic paralysis (TPP), an endocrine channelopathy, and is the most common cause of acquired periodic paralysis. Typically, paralytic attacks cease when hyperthyroidism is abolished, and recur if hyperthyroidism returns. TPP is often underdiagnosed, as it has diverse periodicity, duration and intensity. The age at which patients develop TPP closely follows the age at which thyrotoxicosis occurs. All ethnicities can be affected, but TPP is most prevalent in people of Asian and, secondly, Latin American descent. TPP is characterized by hypokalemia, suppressed TSH levels and increased levels of thyroid hormones. Nonselective β adrenergic blockers, such as propranolol, are an efficient adjuvant to antithyroid drugs to prevent paralysis; however, an early and definitive treatment should always be pursued. Evidence indicates that TPP results from the combination of genetic susceptibility, thyrotoxicosis and environmental factors (such as a high-carbohydrate diet). We believe that excess T(3) modifies the insulin sensitivity of skeletal muscle and pancreatic β cells and thus alters potassium homeostasis, but only leads to a depolarization-induced acute loss of muscle excitability in patients with inherited ion channel mutations. An integrated etiopathophysiological model is proposed based on molecular findings and knowledge gained from long-term follow-up of patients with TPP.
Collapse
Affiliation(s)
- Rui M B Maciel
- Department of Medicine, Universidade Federal de São Paulo, Rua Pedro de Toledo, São Paulo, Brazil
| | | | | |
Collapse
|
68
|
Van Horn WD, Vanoye CG, Sanders CR. Working model for the structural basis for KCNE1 modulation of the KCNQ1 potassium channel. Curr Opin Struct Biol 2011; 21:283-91. [PMID: 21296569 DOI: 10.1016/j.sbi.2011.01.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Revised: 01/03/2011] [Accepted: 01/04/2011] [Indexed: 12/19/2022]
Abstract
The voltage-gated potassium channel KCNQ1 (Kv7.1) is modulated by KCNE1 (minK) to generate the I(Ks) current crucial to heartbeat. Defects in either protein result in serious cardiac arrhythmias. Recently developed structural models of the open and closed state KCNQ1/KCNE1 complexes offer a compelling explanation for how KCNE1 slows channel opening and provides a platform from which to refine and test hypotheses for other aspects of KCNE1 modulation. These working models were developed using an integrative approach based on results from nuclear magnetic resonance spectroscopy, electrophysiology, biochemistry, and computational methods-an approach that can be applied iteratively for model testing and revision. We present a critical review of these structural models, illustrating the strengths and challenges of the integrative approach.
Collapse
Affiliation(s)
- Wade D Van Horn
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232-8725, USA
| | | | | |
Collapse
|
69
|
Roura-Ferrer M, Solé L, Oliveras A, Dahan R, Bielanska J, Villarroel A, Comes N, Felipe A. Impact of KCNE subunits on KCNQ1 (Kv7.1) channel membrane surface targeting. J Cell Physiol 2010; 225:692-700. [PMID: 20533308 DOI: 10.1002/jcp.22265] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The KCNQ1 (Kv7.1) channel plays an important role in cardiovascular physiology. Cardiomyocytes co-express KCNQ1 with KCNE1-5 proteins. KCNQ1 may co-associate with multiple KCNE regulatory subunits to generate different biophysically and pharmacologically distinct channels. Increasing evidence indicates that the location and targeting of channels are important determinants of their function. In this context, the presence of K(+) channels in sphingolipid-cholesterol-enriched membrane microdomains (lipid rafts) is under investigation. Lipid rafts are important for cardiovascular functioning. We aimed to determine whether KCNE subunits modify the localization and targeting of KCNQ1 channels in lipid rafts microdomains. HEK-293 cells were transiently transfected with KCNQ1 and KCNE1-5, and their traffic and presence in lipid rafts were analyzed. Only KCNQ1 and KCNE3, when expressed alone, co-localized in raft fractions. In addition, while KCNE2 and KCNE5 notably stained the cell surface, KCNQ1 and the rest of the KCNEs showed strong intracellular retention. KCNQ1 targets multiple membrane surface microdomains upon association with KCNE peptides. Thus, while KCNQ1/KCNE1 and KCNQ1/KCNE2 channels target lipid rafts, KCNQ1 associated with KCNE3-5 did not. Channel membrane dynamics, analyzed by fluorescence recovery after photobleaching (FRAP) experiments, further supported these results. In conclusion, the trafficking and targeting pattern of KCNQ1 can be influenced by its association with KCNEs. Since KCNQ1 is crucial for cardiovascular physiology, the temporal and spatial regulations that different KCNE subunits may confer to the channels could have a dramatic impact on membrane electrical activity and putative endocrine regulation.
Collapse
Affiliation(s)
- Meritxell Roura-Ferrer
- Molecular Physiology Laboratory, Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Barcelona, Spain
| | | | | | | | | | | | | | | |
Collapse
|
70
|
Menéndez ST, Rodrigo JP, Allonca E, García-Carracedo D, Alvarez-Alija G, Casado-Zapico S, Fresno MF, Rodríguez C, Suárez C, García-Pedrero JM. Expression and clinical significance of the Kv3.4 potassium channel subunit in the development and progression of head and neck squamous cell carcinomas. J Pathol 2010; 221:402-10. [PMID: 20593490 DOI: 10.1002/path.2722] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The concept of ion channels as membrane therapeutic targets and diagnostic/prognostic biomarkers has attracted growing attention. We therefore investigated the expression pattern and clinical significance of the Kv3.4 potassium channel subunit during the development and progression of head and neck squamous cell carcinomas (HNSCCs). KCNC4 mRNA levels were determined by real-time RT-PCR in both HNSCC tissue specimens and derived cell lines. Kv3.4 protein expression was evaluated by immunohistochemistry in paraffin-embedded tissue specimens from 84 patients with laryngeal/pharyngeal squamous cell carcinomas and 67 patients with laryngeal dysplasias. Molecular alterations were correlated with clinicopathological parameters and patient outcome. Increased KCNC4 mRNA levels were found in 15 (54%) of 28 tumours, compared to the corresponding normal epithelia and varied mRNA levels were detected in 12 HNSCC-derived cell lines analysed. Increased Kv3.4 protein expression was observed in 34 (40%) of 84 carcinomas and also at early stages of HNSCC tumourigenesis. Thus, 35 (52%) of 67 laryngeal lesions displayed Kv3.4-positive staining in the dysplastic areas, whereas both stromal cells and normal adjacent epithelia exhibited negligible expression. No significant correlations were found between Kv3.4-positive expression in HNSCC and clinical data; however, Kv3.4 expression tended to diminish in advanced-stage tumours. Interestingly, patients carrying Kv3.4-positive dysplasias experienced a significantly higher laryngeal cancer incidence than did those with negative lesions (p = 0.0209). In addition, functional studies using HNSCC cells revealed that inhibition of Kv3.4 expression by siRNA leads to the inhibition of cell proliferation via selective cell cycle arrest at the G2/M phase without affecting apoptosis. Collectively, these data demonstrate for the first time that Kv3.4 expression is frequently increased during HNSCC tumourigenesis and correlated significantly with a higher cancer risk. Our findings support a role for Kv3.4 in malignant transformation and provide original evidence for the potential clinical utility of Kv3.4 expression as a biomarker for cancer risk assessment.
Collapse
Affiliation(s)
- Sofía Tirados Menéndez
- Servicio de Otorrinolaringología, Hospital Universitario Central de Asturias and Instituto Universitario de Oncología del Principado de Asturias, Oviedo, Spain
| | | | | | | | | | | | | | | | | | | |
Collapse
|
71
|
Abstract
Since the first discovery of Kvbeta-subunits more than 15 years ago, many more ancillary Kv channel subunits were characterized, for example, KChIPs, KCNEs, and BKbeta-subunits. The ancillary subunits are often integral parts of native Kv channels, which, therefore, are mostly multiprotein complexes composed of voltage-sensing and pore-forming Kvalpha-subunits and of ancillary or beta-subunits. Apparently, Kv channels need the ancillary subunits to fulfill their many different cell physiological roles. This is reflected by the large structural diversity observed with ancillary subunit structures. They range from proteins with transmembrane segments and extracellular domains to purely cytoplasmic proteins. Ancillary subunits modulate Kv channel gating but can also have a great impact on channel assembly, on channel trafficking to and from the cellular surface, and on targeting Kv channels to different cellular compartments. The importance of the role of accessory subunits is further emphasized by the number of mutations that are associated in both humans and animals with diseases like hypertension, epilepsy, arrhythmogenesis, periodic paralysis, and hypothyroidism. Interestingly, several ancillary subunits have in vitro enzymatic activity; for example, Kvbeta-subunits are oxidoreductases, or modulate enzymatic activity, i.e., KChIP3 modulates presenilin activity. Thus different modes of beta-subunit association and of functional impact on Kv channels can be delineated, making it difficult to extract common principles underlying Kvalpha- and beta-subunit interactions. We critically review present knowledge on the physiological role of ancillary Kv channel subunits and their effects on Kv channel properties.
Collapse
Affiliation(s)
- Olaf Pongs
- Institut für Neurale Signalverarbeitung, Zentrum für Molekulare Neurobiologie Hamburg, Universitätsklinikum Hamburg-Eppendorf, Universität Hamburg, Hamburg, Germany.
| | | |
Collapse
|
72
|
Leblanc N. Kv3.4, a key signalling molecule controlling the cell cycle and proliferation of human arterial smooth muscle cells. Cardiovasc Res 2010; 86:351-2. [PMID: 20378681 DOI: 10.1093/cvr/cvq106] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
73
|
Goncharuk SA, Shulga AA, Ermolyuk YS, Kuzmichev PK, Sobol VA, Bocharov EV, Chupin VV, Arseniev AS, Kirpichnikov MP. Bacterial synthesis, purification, and solubilization of membrane protein KCNE3, a regulator of voltage-gated potassium channels. BIOCHEMISTRY (MOSCOW) 2010; 74:1344-9. [PMID: 19961415 DOI: 10.1134/s0006297909120074] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
An efficient method is described for production of membrane protein KCNE3 and its isotope labeled derivatives ((15)N-, (15)N-/13C-) in amounts sufficient for structural-functional investigations. The purified protein preparation within different detergent micelles was characterized using dynamic light scattering, CD spectroscopy, and NMR spectroscopy. It is shown that within DPC/LDAO micelles the protein is in monomeric form and acquires mainly alpha-helical conformation. The existence of cross-peaks for all glycines of the (15)N-HSQC NMR spectra as well as relatively small line widths (~20 Hz) confirm the high quality of the preparation and the possibility of obtaining structural-dynamic information on KCNE3 by high resolution heteronuclear NMR spectroscopy.
Collapse
Affiliation(s)
- S A Goncharuk
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.
| | | | | | | | | | | | | | | | | |
Collapse
|
74
|
Miguel-Velado E, Pérez-Carretero FD, Colinas O, Cidad P, Heras M, López-López JR, Pérez-García MT. Cell cycle-dependent expression of Kv3.4 channels modulates proliferation of human uterine artery smooth muscle cells. Cardiovasc Res 2010; 86:383-91. [PMID: 20093253 DOI: 10.1093/cvr/cvq011] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
AIMS Vascular smooth muscle cell (VSMC) proliferation is involved in cardiovascular pathologies associated with unwanted arterial wall remodelling. Coordinated changes in the expression of several K+ channels have been found to be important elements in the phenotypic switch of VSMCs towards proliferation. We have previously demonstrated the association of functional expression of Kv3.4 channels with proliferation of human uterine VSMCs. Here, we sought to gain deeper insight on the relationship between Kv3.4 channels and cell cycle progression in this preparation. METHODS AND RESULTS Expression and function of Kv3.4 channels along the cell cycle was explored in uterine VSMCs synchronized at different checkpoints, combining real-time PCR, western blotting, and electrophysiological techniques. Flow cytometry, Ki67 expression and BrdU incorporation techniques allowed us to explore the effects of Kv3.4 channels blockade on cell cycle distribution. We found cyclic changes in Kv3.4 and MiRP2 mRNA and protein expression along the cell cycle. Functional studies showed that Kv3.4 current amplitude and Kv3.4 channels contribution to cell excitability increased in proliferating cells. Finally, both Kv3.4 blockers and Kv3.4 knockdown with siRNA reduced the proportion of proliferating VSMCs. CONCLUSION Our data indicate that Kv3.4 channels exert a permissive role in the cell cycle progression of proliferating uterine VSMCs, as their blockade induces cell cycle arrest after G2/M phase completion. The modulation of resting membrane potential (V(M)) by Kv3.4 channels in proliferating VSMCs suggests that their role in cell cycle progression could be at least in part mediated by their contribution to the hyperpolarizing signal needed to progress through the G1 phase.
Collapse
Affiliation(s)
- Eduardo Miguel-Velado
- Departamento de Bioquímica y Biología Molecular y Fisiología e Instituto de Biología y Genética Molecular , Universidad de Valladolid y CSIC, Valladolid, Spain
| | | | | | | | | | | | | |
Collapse
|
75
|
Preston P, Wartosch L, Günzel D, Fromm M, Kongsuphol P, Ousingsawat J, Kunzelmann K, Barhanin J, Warth R, Jentsch TJ. Disruption of the K+ channel beta-subunit KCNE3 reveals an important role in intestinal and tracheal Cl- transport. J Biol Chem 2010; 285:7165-75. [PMID: 20051516 DOI: 10.1074/jbc.m109.047829] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The KCNE3 beta-subunit constitutively opens outwardly rectifying KCNQ1 (Kv7.1) K(+) channels by abolishing their voltage-dependent gating. The resulting KCNQ1/KCNE3 heteromers display enhanced sensitivity to K(+) channel inhibitors like chromanol 293B. KCNE3 was also suggested to modify biophysical properties of several other K(+) channels, and a mutation in KCNE3 was proposed to underlie forms of human periodic paralysis. To investigate physiological roles of KCNE3, we now disrupted its gene in mice. kcne3(-/-) mice were viable and fertile and displayed neither periodic paralysis nor other obvious skeletal muscle abnormalities. KCNQ1/KCNE3 heteromers are present in basolateral membranes of intestinal and tracheal epithelial cells where they might facilitate transepithelial Cl(-) secretion through basolateral recycling of K(+) ions and by increasing the electrochemical driving force for apical Cl(-) exit. Indeed, cAMP-stimulated electrogenic Cl(-) secretion across tracheal and intestinal epithelia was drastically reduced in kcne3(-/-) mice. Because the abundance and subcellular localization of KCNQ1 was unchanged in kcne3(-/-) mice, the modification of biophysical properties of KCNQ1 by KCNE3 is essential for its role in intestinal and tracheal transport. Further, these results suggest KCNE3 as a potential modifier gene in cystic fibrosis.
Collapse
Affiliation(s)
- Patricia Preston
- Leibniz-Institut für Molekulare Pharmakologie and Max-Delbrück-Centrum für Molekulare Medizin, 13125 Berlin, Germany
| | | | | | | | | | | | | | | | | | | |
Collapse
|
76
|
Jurkat-Rott K, Lerche H, Weber Y, Lehmann-Horn F. Hereditary channelopathies in neurology. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 686:305-34. [PMID: 20824453 DOI: 10.1007/978-90-481-9485-8_18] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Ion channelopathies are caused by malfunction or altered regulation of ion channel proteins due to hereditary or acquired protein changes. In neurology, main phenotypes include certain forms of epilepsy, ataxia, migraine, neuropathic pain, myotonia, and muscle weakness including myasthenia and periodic paralyses. The total prevalence of monogenic channelopathies in neurology is about 35:100,000. Susceptibility-related mutations further increase the relevance of channel genes in medicine considerably. As many disease mechanisms have been elucidated by functional characterization on the molecular level, the channelopathies are regarded as model disorders for pathogenesis and treatment of non-monogenic forms of epilepsy and migraine. As more than 35% of marketed drugs target ion channels, there is a high chance to identify compounds that counteract the effects of the mutations.
Collapse
|
77
|
De novo deletion of chromosome 11q13.4–q14.3 in a boy with microcephaly, ptosis and developmental delay. Eur J Med Genet 2010; 53:50-3. [DOI: 10.1016/j.ejmg.2009.10.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2009] [Accepted: 10/17/2009] [Indexed: 11/20/2022]
|
78
|
Abstract
The human genome encodes 40 voltage-gated K(+) channels (K(V)), which are involved in diverse physiological processes ranging from repolarization of neuronal and cardiac action potentials, to regulating Ca(2+) signalling and cell volume, to driving cellular proliferation and migration. K(V) channels offer tremendous opportunities for the development of new drugs to treat cancer, autoimmune diseases and metabolic, neurological and cardiovascular disorders. This Review discusses pharmacological strategies for targeting K(V) channels with venom peptides, antibodies and small molecules, and highlights recent progress in the preclinical and clinical development of drugs targeting the K(V)1 subfamily, the K(V)7 subfamily (also known as KCNQ), K(V)10.1 (also known as EAG1 and KCNH1) and K(V)11.1 (also known as HERG and KCNH2) channels.
Collapse
|
79
|
Castañeda O, Harvey AL. Discovery and characterization of cnidarian peptide toxins that affect neuronal potassium ion channels. Toxicon 2009; 54:1119-24. [DOI: 10.1016/j.toxicon.2009.02.032] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
|
80
|
Hedley PL, Jørgensen P, Schlamowitz S, Moolman-Smook J, Kanters JK, Corfield VA, Christiansen M. The genetic basis of Brugada syndrome: a mutation update. Hum Mutat 2009; 30:1256-66. [PMID: 19606473 DOI: 10.1002/humu.21066] [Citation(s) in RCA: 125] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Brugada syndrome (BrS) is a condition characterized by a distinct ST-segment elevation in the right precordial leads of the electrocardiogram and, clinically, by an increased risk of cardiac arrhythmia and sudden death. The condition predominantly exhibits an autosomal dominant pattern of inheritance with an average prevalence of 5:10,000 worldwide. Currently, more than 100 mutations in seven genes have been associated with BrS. Loss-of-function mutations in SCN5A, which encodes the alpha-subunit of the Na(v)1.5 sodium ion channel conducting the depolarizing I(Na) current, causes 15-20% of BrS cases. A few mutations have been described in GPD1L, which encodes glycerol-3-phosphate dehydrogenase-1 like protein; CACNA1C, which encodes the alpha-subunit of the Ca(v)1.2 ion channel conducting the depolarizing I(L,Ca) current; CACNB2, which encodes the stimulating beta2-subunit of the Ca(v)1.2 ion channel; SCN1B and SCN3B, which, in the heart, encodes beta-subunits of the Na(v)1.5 sodium ion channel, and KCNE3, which encodes the ancillary inhibitory beta-subunit of several potassium channels including the Kv4.3 ion channel conducting the repolarizing potassium I(to) current. BrS exhibits variable expressivity, reduced penetrance, and "mixed phenotypes," where families contain members with BrS as well as long QT syndrome, atrial fibrillation, short QT syndrome, conduction disease, or structural heart disease, have also been described.
Collapse
Affiliation(s)
- Paula L Hedley
- Department of Clinical Biochemistry and Immunology, Statens Serum Institut, Copenhagen, Denmark
| | | | | | | | | | | | | |
Collapse
|
81
|
Sacconi S, Simkin D, Arrighi N, Chapon F, Larroque MM, Vicart S, Sternberg D, Fontaine B, Barhanin J, Desnuelle C, Bendahhou S. Mechanisms underlying Andersen's syndrome pathology in skeletal muscle are revealed in human myotubes. Am J Physiol Cell Physiol 2009; 297:C876-85. [DOI: 10.1152/ajpcell.00519.2008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Andersen's syndrome is a rare disorder that has been defined with a triad: periodic paralysis, cardiac arrhythmia, and development anomalies. Muscle weakness has been reported in two-thirds of the patients. KCNJ2 remains the only gene linked to Andersen's syndrome; this gene encodes for the α-subunit of the strong inward-rectifier K+ channel Kir2.1. Several studies have shown that Andersen's syndrome mutations lead to a loss of function of the K+ channel activity in vitro. However, ex vivo studies on isolated patient muscle tissue have not been reported. We have performed muscle biopsies of controls and patients presenting with clinically and genetically defined Andersen's syndrome disorder. Myoblasts were cultured and characterized morphologically and functionally using the whole cell patch-clamp technique. No morphological difference was observed between Andersen's syndrome and control myoblasts at each passage of the cell culture. Cellular proliferation and viability were quantified in parallel with direct cell counts and showed no difference between control and Andersen's syndrome patients. Moreover, our data show no significant difference in myoblast fusion index among Andersen's syndrome and control patients. Current recordings carried out on myotubes revealed the absence of an inwardly rectifying Ba2+-sensitive current in affected patient cells. One consequence of the Ik1 current loss in Andersen's syndrome myotubes is a shift of the resting membrane potential toward depolarizing potentials. Our data describe for the first time the functional consequences of Andersen's syndrome mutations ex vivo and provide clues to the K+ channel pathophysiology in skeletal muscle.
Collapse
Affiliation(s)
- S. Sacconi
- Centre Hospitalier Universitaire of Nice, Centre de Référence Maladies Neuromusculaires et Sclérose Latérale Amyotrophique, Institut National de la Santé et de la Recherche Médicale Unité 638, Institut Fédératif de Recherche 50, Nice
| | - D. Simkin
- University of Nice Sophia Antipolis, Transport Ionique Aspects Normaux et Pathologiques, Formation de Recherche en Evolution 3093 Centre National de la Recherche Scientifique, Parc Valrose, Nice
| | - N. Arrighi
- Centre Hospitalier Universitaire of Nice, Centre de Référence Maladies Neuromusculaires et Sclérose Latérale Amyotrophique, Institut National de la Santé et de la Recherche Médicale Unité 638, Institut Fédératif de Recherche 50, Nice
| | - F. Chapon
- Centre Hospitalier Universitaire of Caen, Service de Neurologie et Laboratoire de Neuropathologie, Caen
| | - M. M. Larroque
- University of Nice Sophia Antipolis, Institut de Pharmacologie Moléculaire et Cellulaire, Unité Mixte de Recherche 6097 Centre National de la Recherche Scientifique, Sophia Antipolis, Valbonne
| | - S. Vicart
- Centre de Référence des Canalopathies Musculaires, Fédération des Maladies du Système Nerveux; Université Pierre et Marie Curie, Unité Mixte de Recherche S546; Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche 546, Paris; and
| | - D. Sternberg
- Biochemistry and Genetics, Hôpital Pitié-Salpêtrière, Assistance Publique, Hôpitaux de Paris, and Unité Mixte de Recherche 546, Université Pierre et Marie Curie and Institut National de la Santé et de la Recherche Médicale, Paris, France
| | - B. Fontaine
- Centre de Référence des Canalopathies Musculaires, Fédération des Maladies du Système Nerveux; Université Pierre et Marie Curie, Unité Mixte de Recherche S546; Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche 546, Paris; and
| | - J. Barhanin
- University of Nice Sophia Antipolis, Transport Ionique Aspects Normaux et Pathologiques, Formation de Recherche en Evolution 3093 Centre National de la Recherche Scientifique, Parc Valrose, Nice
| | - C. Desnuelle
- Centre Hospitalier Universitaire of Nice, Centre de Référence Maladies Neuromusculaires et Sclérose Latérale Amyotrophique, Institut National de la Santé et de la Recherche Médicale Unité 638, Institut Fédératif de Recherche 50, Nice
| | - S. Bendahhou
- University of Nice Sophia Antipolis, Transport Ionique Aspects Normaux et Pathologiques, Formation de Recherche en Evolution 3093 Centre National de la Recherche Scientifique, Parc Valrose, Nice
| |
Collapse
|
82
|
Ke T, Gomez CR, Mateus HE, Castano JA, Wang QK. Novel CACNA1S mutation causes autosomal dominant hypokalemic periodic paralysis in a South American family. J Hum Genet 2009; 54:660-4. [DOI: 10.1038/jhg.2009.92] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
83
|
Clancy SM, Chen B, Bertaso F, Mamet J, Jegla T. KCNE1 and KCNE3 beta-subunits regulate membrane surface expression of Kv12.2 K(+) channels in vitro and form a tripartite complex in vivo. PLoS One 2009; 4:e6330. [PMID: 19623261 PMCID: PMC2710002 DOI: 10.1371/journal.pone.0006330] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2009] [Accepted: 06/17/2009] [Indexed: 01/14/2023] Open
Abstract
Voltage-gated potassium channels that activate near the neuronal resting membrane potential are important regulators of excitation in the nervous system, but their functional diversity is still not well understood. For instance, Kv12.2 (ELK2, KCNH3) channels are highly expressed in the cerebral cortex and hippocampus, and although they are most likely to contribute to resting potassium conductance, surprisingly little is known about their function or regulation. Here we demonstrate that the auxiliary MinK (KCNE1) and MiRP2 (KCNE3) proteins are important regulators of Kv12.2 channel function. Reduction of endogenous KCNE1 or KCNE3 expression by siRNA silencing, significantly increased macroscopic Kv12.2 currents in Xenopus oocytes by around 4-fold. Interestingly, an almost 9-fold increase in Kv12.2 currents was observed with the dual injection of KCNE1 and KCNE3 siRNA, suggesting an additive effect. Consistent with these findings, over-expression of KCNE1 and/or KCNE3 suppressed Kv12.2 currents. Membrane surface biotinylation assays showed that surface expression of Kv12.2 was significantly increased by KCNE1 and KCNE3 siRNA, whereas total protein expression of Kv12.2 was not affected. KCNE1 and KCNE3 siRNA shifted the voltages for half-maximal activation to more hyperpolarized voltages, indicating that KCNE1 and KCNE3 may also inhibit activation gating of Kv12.2. Native co-immunoprecipitation assays from mouse brain membranes imply that KCNE1 and KCNE3 interact with Kv12.2 simultaneously in vivo, suggesting the existence of novel KCNE1-KCNE3-Kv12.2 channel tripartite complexes. Together these data indicate that KCNE1 and KCNE3 interact directly with Kv12.2 channels to regulate channel membrane trafficking.
Collapse
Affiliation(s)
- Sinead M. Clancy
- Department of Cell Biology, Institute for Childhood and Neglected Diseases, The Scripps Research Institute, La Jolla, California, United States of America
| | - Bihan Chen
- Department of Cell Biology, Institute for Childhood and Neglected Diseases, The Scripps Research Institute, La Jolla, California, United States of America
| | - Federica Bertaso
- Department of Cell Biology, Institute for Childhood and Neglected Diseases, The Scripps Research Institute, La Jolla, California, United States of America
| | - Julien Mamet
- Department of Cell Biology, Institute for Childhood and Neglected Diseases, The Scripps Research Institute, La Jolla, California, United States of America
| | - Timothy Jegla
- Department of Cell Biology, Institute for Childhood and Neglected Diseases, The Scripps Research Institute, La Jolla, California, United States of America
- * E-mail:
| |
Collapse
|
84
|
Ohno S, Toyoda F, Zankov DP, Yoshida H, Makiyama T, Tsuji K, Honda T, Obayashi K, Ueyama H, Shimizu W, Miyamoto Y, Kamakura S, Matsuura H, Kita T, Horie M. NovelKCNE3mutation reduces repolarizing potassium current and associated with long QT syndrome. Hum Mutat 2009; 30:557-63. [DOI: 10.1002/humu.20834] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
|
85
|
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.
Collapse
|
86
|
Diochot S, Lazdunski M. Sea anemone toxins affecting potassium channels. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2009; 46:99-122. [PMID: 19184586 DOI: 10.1007/978-3-540-87895-7_4] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The great diversity of K(+) channels and their wide distribution in many tissues are associated with important functions in cardiac and neuronal excitability that are now better understood thanks to the discovery of animal toxins. During the past few decades, sea anemones have provided a variety of toxins acting on voltage-sensitive sodium and, more recently, potassium channels. Currently there are three major structural groups of sea anemone K(+) channel (SAK) toxins that have been characterized. Radioligand binding and electrophysiological experiments revealed that each group contains peptides displaying selective activities for different subfamilies of K(+) channels. Short (35-37 amino acids) peptides in the group I display pore blocking effects on Kv1 channels. Molecular interactions of SAK-I toxins, important for activity and binding on Kv1 channels, implicate a spot of three conserved amino acid residues (Ser, Lys, Tyr) surrounded by other less conserved residues. Long (58-59 amino acids) SAK-II peptides display both enzymatic and K(+) channel inhibitory activities. Medium size (42-43 amino acid) SAK-III peptides are gating modifiers which interact either with cardiac HERG or Kv3 channels by altering their voltage-dependent properties. SAK-III toxins bind to the S3C region in the outer vestibule of Kv channels. Sea anemones have proven to be a rich source of pharmacological tools, and some of the SAK toxins are now useful drugs for the diagnosis and treatment of autoimmune diseases.
Collapse
Affiliation(s)
- Sylvie Diochot
- Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifi que, Université de Nice-Sophia-Antipolis, 660 Route des Lucioles, Valbonne, 06560, France
| | | |
Collapse
|
87
|
Kurokawa J, Bankston JR, Kaihara A, Chen L, Furukawa T, Kass RS. KCNE variants reveal a critical role of the beta subunit carboxyl terminus in PKA-dependent regulation of the IKs potassium channel. Channels (Austin) 2009; 3:16-24. [PMID: 19077539 DOI: 10.4161/chan.3.1.7387] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Co-assembly of KCNQ1 with different accessory, or beta, subunits that are members of the KCNE family results in potassium (K+) channels that conduct functionally distinct currents. The alpha subunit KCNQ1 conducts a slowly activated delayed rectifier K+ current (IKs), a major contributor to cardiac repolarization, when co-assembled with KCNE1 and channels that favor the open state when co-assembled with either KCNE2 or KCNE3. In the heart, stimulation of the sympathetic nervous system enhances IKs. A macromolecular signaling complex of the IKs channel including the targeting protein Yotiao coordinates up or downregulation of channel activity by protein kinase A (PKA) phosphorylation and dephosphorylation of molecules in the complex. beta-adrenergic receptor mediated IKs upregulation, a functional consequence of PKA phosphorylation of the KCNQ1 amino terminus (N-T), requires co-expression of KCNQ1/Yotiao with KCNE1. Here, we report that co-expression of KCNE2, like KCNE1, confers a functional channel response to KCNQ1 phosphorylation, but co-expression of KCNE3 does not. Amino acid sequence comparison among the KCNE peptides, and KCNE1 truncation experiments, reveal a segment of the predicted intracellular KCNE1 carboxyl terminus (C-T) that is necessary for functional transduction of PKA phosphorylated KCNQ1. Moreover, chimera analysis reveals a region of KCNE1 sufficient to confer cAMP-dependent functional regulation upon the KCNQ1_KCNE3_Yotiao channel. The property of specific beta subunits to transduce post-translational regulation of alpha subunits of ion channels adds another dimension to our understanding molecular mechanisms underlying the diversity of regulation of native K+ channels.
Collapse
Affiliation(s)
- Junko Kurokawa
- Department of Bio-Informational Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan.
| | | | | | | | | | | |
Collapse
|
88
|
Maffie J, Rudy B. Weighing the evidence for a ternary protein complex mediating A-type K+ currents in neurons. J Physiol 2008; 586:5609-23. [PMID: 18845608 DOI: 10.1113/jphysiol.2008.161620] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The subthreshold-operating A-type K(+) current in neurons (I(SA)) has important roles in the regulation of neuronal excitability, the timing of action potential firing and synaptic integration and plasticity. The channels mediating this current (Kv4 channels) have been implicated in epilepsy, the control of dopamine release, and the regulation of pain plasticity. It has been proposed that Kv4 channels in neurons are ternary complexes of three types of protein: pore forming subunits of the Kv4 subfamily and two types of auxiliary subunits, the Ca(2+) binding proteins KChIPs and the dipeptidyl peptidase-like proteins (DPPLs) DPP6 (also known as DPPX) and DPP10 (4 molecules of each per channel for a total of 12 proteins in the complex). Here we consider the evidence supporting this hypothesis. Kv4 channels in many neurons are likely to be ternary complexes of these three types of protein. KChIPs and DPPLs are required to efficiently traffic Kv4 channels to the plasma membrane and regulate the functional properties of the channels. These proteins may also be important in determining the localization of the channels to specific neuronal compartments, their dynamics, and their response to neuromodulators. A surprisingly large number of additional proteins have been shown to modify Kv4 channels in heterologous expression systems, but their association with native Kv4 channels in neurons has not been properly validated. A critical consideration of the evidence suggests that it is unlikely that association of Kv4 channels with these additional proteins is widespread in the CNS. However, we cannot exclude that some of these proteins may associate with the channels transiently or in specific neurons or neuronal compartments, or that they may associate with the channels in other tissues.
Collapse
Affiliation(s)
- Jonathon Maffie
- Smilow Neuroscience Program, Department of Physiology and Neuroscience, New York University School of Medicine, Smilow Research Center, 522 First Avenue, 6th Floor, New York, NY 10016, USA
| | | |
Collapse
|
89
|
|
90
|
Heitzmann D, Warth R. Physiology and pathophysiology of potassium channels in gastrointestinal epithelia. Physiol Rev 2008; 88:1119-82. [PMID: 18626068 DOI: 10.1152/physrev.00020.2007] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Epithelial cells of the gastrointestinal tract are an important barrier between the "milieu interne" and the luminal content of the gut. They perform transport of nutrients, salts, and water, which is essential for the maintenance of body homeostasis. In these epithelia, a variety of K(+) channels are expressed, allowing adaptation to different needs. This review provides an overview of the current literature that has led to a better understanding of the multifaceted function of gastrointestinal K(+) channels, thereby shedding light on pathophysiological implications of impaired channel function. For instance, in gastric mucosa, K(+) channel function is a prerequisite for acid secretion of parietal cells. In epithelial cells of small intestine, K(+) channels provide the driving force for electrogenic transport processes across the plasma membrane, and they are involved in cell volume regulation. Fine tuning of salt and water transport and of K(+) homeostasis occurs in colonic epithelia cells, where K(+) channels are involved in secretory and reabsorptive processes. Furthermore, there is growing evidence for changes in epithelial K(+) channel expression during cell proliferation, differentiation, apoptosis, and, under pathological conditions, carcinogenesis. In the future, integrative approaches using functional and postgenomic/proteomic techniques will help us to gain comprehensive insights into the role of K(+) channels of the gastrointestinal tract.
Collapse
Affiliation(s)
- Dirk Heitzmann
- Institute of Physiology and Clinic and Policlinic for Internal Medicine II, Regensburg, Germany
| | | |
Collapse
|
91
|
Levy DI, Wanderling S, Biemesderfer D, Goldstein SAN. MiRP3 acts as an accessory subunit with the BK potassium channel. Am J Physiol Renal Physiol 2008; 295:F380-7. [PMID: 18463315 DOI: 10.1152/ajprenal.00598.2007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
MinK-related peptides (MiRPs) are single-span membrane proteins that assemble with specific voltage-gated K+ (Kv) channel alpha-subunits to establish gating kinetics, unitary conductance, expression level, and pharmacology of the mixed complex. MiRP3 (encoded by the KCNE4 gene) has been shown to alter the behavior of some Kv alpha-subunits in vitro but its natural partners and physiologic functions are unknown. Seeking in vivo partners for MiRP3, immunohistochemistry was used to localize its expression to a unique subcellular site, the apical membrane of renal intercalated cells, where one potassium channel type has been recorded, the calcium- and voltage-gated channel BK. Overlapping staining of these two proteins was found in rabbit intercalated cells, and MiRP3 and BK subunits expressed in tissue culture cells were found to form detergent-stable complexes. Electrophysiologic and biochemical evaluation showed MiRP3 to act on BK to reduce current density in two fashions: shifting the current-voltage relationship to more depolarized voltages in a calcium-dependent fashion ( approximately 10 mV at normal intracellular calcium levels) and accelerating degradation of MiRP3-BK complexes. The findings suggest a role for MiRP3 modulation of BK-dependent urinary potassium excretion.
Collapse
Affiliation(s)
- Daniel I Levy
- Department of Medicine, Biological Sciences Division, University of Chicago, Chicago, Illinois, USA.
| | | | | | | |
Collapse
|
92
|
Vendrame F, Verrienti A, Parlapiano C, Filetti S, Dotta F, Morano S. Thyrotoxic periodic paralysis in an Italian man: clinical manifestation and genetic analysis. Ann Clin Biochem 2008; 45:218-20. [DOI: 10.1258/acb.2007.007117] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In Western countries, thyrotoxic periodic paralysis (TPP) is a rare condition with only sporadic cases described so far. Here, we describe a 29-year-old Italian man who presented with leg weakness and hypokalaemia. Treatment with intravenous potassium resulted in a rapid resolution of symptoms. TPP as the underlying cause was suggested by suppressed thyroid-stimulating hormone (TSH), elevated free T3 and free T4, and the presence of TSH-receptor antibodies (TRAB). Genetic analysis showed no mutations in the candidate exons of calcium ( CACN1AS), potassium ( KCNE3) and sodium ( SCN4A) channel genes. However, we identified the presence of two single nucleotide polymorphisms (SNPs), 1491C > T and 1551 T > C, in exon 11 of the CACN1AS gene. Although the 1491C > T SNP is not apparently involved in the pathogenesis of the disease, the 1551 T > C SNP has been associated with TPP in Asians and reported in only one case in European Caucasians. Further investigations are needed to clarify whether such polymorphisms have a role in the disease pathogenesis in Caucasians.
Collapse
Affiliation(s)
- Francesco Vendrame
- Diabetes Research Institute, Miller School of Medicine, University of Miami, Miami, FL 33136,USA
- Department of Clinical Sciences, University ‘La Sapienza’, 00161 Rome, Italy
| | - Antonella Verrienti
- Department of Clinical Sciences, University ‘La Sapienza’, 00161 Rome, Italy
| | - Claudio Parlapiano
- Department of Clinical Sciences, University ‘La Sapienza’, 00161 Rome, Italy
| | - Sebastiano Filetti
- Department of Clinical Sciences, University ‘La Sapienza’, 00161 Rome, Italy
| | - Francesco Dotta
- Diabetes Unit, Department of Internal Medicine, Endocrine and Metabolic Sciences and Biochemistry, University of Siena, 53100 Siena, Italy
| | - Susanna Morano
- Department of Clinical Sciences, University ‘La Sapienza’, 00161 Rome, Italy
| |
Collapse
|
93
|
Ozaki H, Mori K, Nakagawa Y, Hoshikawa S, Ito S, Yoshida K. Autonomously functioning thyroid nodule associated with thyrotoxic periodic paralysis. Endocr J 2008; 55:113-9. [PMID: 18202530 DOI: 10.1507/endocrj.k07e-017] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Thyrotoxic periodic paralysis (TPP) is mainly associated with Graves' disease but rarely with autonomously functioning thyroid nodule (AFTN). We herein report a case of AFTN associated with TPP in which the latter resolved after (131) I therapy for the former. We analyzed the genes encoding thyrotropin receptor (TSHR), the alpha-subunit of the stimulatory G protein (Gsalpha), calcium channel CACNA1S and potassium channel KCNE3, and found that the patient does not carry the known mutations in these genes. Whereas the pathogenesis of TPP and AFTN remains to be understood, the present case suggests that ion channel defects responsible for familial hypokalemic periodic paralysis may not be associated with TPP, and that mutations in TSHR and Gs alpha genes may be less frequent in AFTN patients in the Japanese population.
Collapse
Affiliation(s)
- Hiroshi Ozaki
- Division of Nephrology, Endocrinology and Vascular Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan
| | | | | | | | | | | |
Collapse
|
94
|
Gain of function in IKs secondary to a mutation in KCNE5 associated with atrial fibrillation. Heart Rhythm 2008; 5:427-35. [PMID: 18313602 DOI: 10.1016/j.hrthm.2007.12.019] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/22/2007] [Accepted: 12/14/2007] [Indexed: 12/12/2022]
Abstract
BACKGROUND Atrial fibrillation (AF) is the most common clinical arrhythmia and a major cause of cardiovascular morbidity and mortality. Among the gene defects previously associated with AF is a gain of function of the slowly activating delayed rectifier potassium current IKs, secondary to mutations in KCNQ1. Coexpression of KCNE5, the gene encoding the MiRP4 beta-subunit, has been shown to reduce IKs. OBJECTIVE The purpose of this study was to test the hypothesis that mutations in KCNE5 are associated with AF in a large cohort of patients with AF. METHODS One-hundred fifty-eight patients with AF were screened for mutations in the coding region of KCNE5. RESULTS A missense mutation involving substitution of a phenylalanine for leucine at position 65 (L65F) was identified in one patient. This patient did not have a history of familial AF, and neither KCNQ1 nor KCNE2 mutations were found. Transient transfection of Chinese hamster ovary (CHO) cells expressing IKs(KCNQ1+KCNE1) with KCNE5 suppressed the developing and tail currents of IKs in a concentration-dependent manner. Transient transfection with KCNE5-L65F failed to suppress IKs, yielding a current indistinguishable from that recorded in the absence of KCNE5. Developing currents recorded during a test pulse to +60 mV and tail currents recorded upon repolarization to -40 mV both showed a significant concentration-dependent gain of function in IKs with expression of KCNE5-L65F vs KCNE5-WT. CONCLUSION The results of this study suggest that a missense mutation in KCNE5 may be associated with nonfamilial or acquired forms of AF. The arrhythmogenic mechanism most likely is a gain of function of IKs.
Collapse
|
95
|
Abstract
Periodic paralyses are rare diseases characterized by severe episodes of muscle weakness concomitant to variations in blood potassium levels. It is thus usual to differentiate hypokalemic, normokalemic, and hyperkalemic periodic paralysis. Except for thyrotoxic hypokalemic periodic paralysis and periodic paralyses secondary to permanent changes of blood potassium levels, all of these diseases are of genetic origin, transmitted with an autosomal-dominant mode of inheritance. Periodic paralyses are channelopathies, that is, diseases caused by mutations in genes encoding ion channels. The culprit genes encode for potassium, calcium, and sodium channels. Mutations of the potassium and calcium channel genes cause periodic paralysis of the same type (Andersen-Tawil syndrome or hypokalemic periodic paralysis). In contrast, distinct mutations in the muscle sodium channel gene are responsible for all different types of periodic paralyses (hyper-, normo-, and hypokalemic). The physiological consequences of the mutations have been studied by patch-clamp techniques and electromyography (EMG). Globally speaking, ion channel mutations modify the cycle of muscle membrane excitability which results in a loss of function (paralysis). Clinical physiological studies using EMG have shown a good correlation between symptoms and EMG parameters, enabling the description of patterns that greatly enhance molecular diagnosis accuracy. The understanding of the genetics and pathophysiology of periodic paralysis has contributed to refine and rationalize therapeutic intervention and will be without doubts the basis of further advances.
Collapse
Affiliation(s)
- Bertrand Fontaine
- INSERM, UMR 546, Paris, France; Université Pierre et Marie Curie-Paris 6, UMR S546 and Assistance Publique-Hôpitaux de Paris, Centre de référence des canalopathies musculaires, Groupe Hospitalier Pitié-Salpêtrière, Paris, France
| |
Collapse
|
96
|
Bett GCL, Rasmusson RL. Modification of K+ channel-drug interactions by ancillary subunits. J Physiol 2007; 586:929-50. [PMID: 18096604 DOI: 10.1113/jphysiol.2007.139279] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Reconciling ion channel alpha-subunit expression with native ionic currents and their pharmacological sensitivity in target organs has proved difficult. In native tissue, many K(+) channel alpha-subunits co-assemble with ancillary subunits, which can profoundly affect physiological parameters including gating kinetics and pharmacological interactions. In this review, we examine the link between voltage-gated potassium ion channel pharmacology and the biophysics of ancillary subunits. We propose that ancillary subunits can modify the interaction between pore blockers and ion channels by three distinct mechanisms: changes in (1) binding site accessibility; (2) orientation of pore-lining residues; (3) the ability of the channel to undergo post-binding conformational changes. Each of these subunit-induced changes has implications for gating, drug affinity and use dependence of their respective channel complexes. A single subunit may modulate its associated alpha-subunit by more than one of these mechanisms. Voltage-gated potassium channels are the site of action of many therapeutic drugs. In addition, potassium channels interact with drugs whose primary target is another channel, e.g. the calcium channel blocker nifedipine, the sodium channel blocker quinidine, etc. Even when K(+) channel block is the intended mode of action, block of related channels in non-target organs, e.g. the heart, can result in major and potentially lethal side-effects. Understanding factors that determine specificity, use dependence and other properties of K(+) channel drug binding are therefore of vital clinical importance. Ancillary subunits play a key role in determining these properties in native tissue, and so understanding channel-subunit interactions is vital to understanding clinical pharmacology.
Collapse
Affiliation(s)
- Glenna C L Bett
- Center for Cellular and Systems Electrophysiology, Department of Physiology and Biophysics, School of Medicine and Biomedical Sciences, 124 Sherman Hall, State University of New York at Buffalo, Buffalo, NY 14214-3005, USA
| | | |
Collapse
|
97
|
Abstract
Toxic thyroid adenoma presenting as hypokalemic periodic paralysis is extraordinarily rare. We describe a 26-year-old Japanese man who suffered from acute and painful muscle weakness of extremity in the morning. Physical examination showed a left anterior neck mass and laboratory tests revealed hypokalemia during his paralysis, and thyrotoxicosis. Neck sonogram showed a solitary nodule in the left lobe of the thyroid. Thyroid scintigraphy revealed a hot nodule of the tumor region with suppressed uptake in the other thyroid area. The tumor was surgically removed and his paralytic attack ceased. No somatic mutation of TSH receptor was found in his thyroid adenoma and no known genetic mutations of ionic channel genes, such as calcium (CACN1S), sodium (SCN4A) and potassium (KCNE3), were found. Although thyrotoxic periodic paralysis is usually accompanied with Graves' disease, thyrotoxicosis of other conditions including Plummer's disease should be considered.
Collapse
Affiliation(s)
- Tetsuya Tagami
- Clinical Research Institute, Division of Endocrinology and Metabolism, Kyoto Medical Center, National Hospital Organization, Japan
| | | | | | | |
Collapse
|
98
|
Aturaliya RN, Fink JL, Davis MJ, Teasdale MS, Hanson KA, Miranda KC, Forrest ARR, Grimmond SM, Suzuki H, Kanamori M, Kai C, Kawai J, Carninci P, Hayashizaki Y, Teasdale RD. Subcellular localization of mammalian type II membrane proteins. Traffic 2007; 7:613-25. [PMID: 16643283 DOI: 10.1111/j.1600-0854.2006.00407.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Application of a computational membrane organization prediction pipeline, MemO, identified putative type II membrane proteins as proteins predicted to encode a single alpha-helical transmembrane domain (TMD) and no signal peptides. MemO was applied to RIKEN's mouse isoform protein set to identify 1436 non-overlapping genomic regions or transcriptional units (TUs), which encode exclusively type II membrane proteins. Proteins with overlapping predicted InterPro and TMDs were reviewed to discard false positive predictions resulting in a dataset comprised of 1831 transcripts in 1408 TUs. This dataset was used to develop a systematic protocol to document subcellular localization of type II membrane proteins. This approach combines mining of published literature to identify subcellular localization data and a high-throughput, polymerase chain reaction (PCR)-based approach to experimentally characterize subcellular localization. These approaches have provided localization data for 244 and 169 proteins. Type II membrane proteins are localized to all major organelle compartments; however, some biases were observed towards the early secretory pathway and punctate structures. Collectively, this study reports the subcellular localization of 26% of the defined dataset. All reported localization data are presented in the LOCATE database (http://www.locate.imb.uq.edu.au).
Collapse
Affiliation(s)
- Rajith N Aturaliya
- Institute for Molecular Bioscience and ARC Centre in Bioinformatics, University of Queensland, St. Lucia, Queensland 4072, Australia
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
99
|
Arimura K, Arimura Y, Ng AR, Sakoda SI, Higuchi I. Muscle membrane excitability after exercise in thyrotoxic periodic paralysis and thyrotoxicosis without periodic paralysis. Muscle Nerve 2007; 36:784-8. [PMID: 17722048 DOI: 10.1002/mus.20865] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We evaluated whether the paralytic attacks in thyrotoxic periodic paralysis (TPP) are primarily due to the abnormal excitability of the muscle membrane caused by a preexisting latent abnormality or to the effects of thyroid hormone. The prolonged exercise (PE) test was used to evaluate muscle membrane excitability in 21 patients with TPP and 11 patients with thyrotoxicosis without paralytic attacks (Tw/oPP) in the hyperthyroid state. The PE tests were compared between the hyperthyroid and euthyroid states in five of the TPP and three of the Tw/oPP patients. Compared to 20 healthy subjects, a significant increase in compound muscle action potential (CMAP) amplitudes immediately after exercise and a significant time-dependent gradual decline in CMAP amplitudes starting from 20 min after exercise were observed in the TPP patients. A significant decline in CMAP amplitudes was also observed in the Tw/oPP patients but only at 50 min after exercise. All of the TPP and Tw/oPP patients had a tendency to improve in the euthyroid state; the PE tests remained abnormal only in the TPP patients. Paralytic attacks in TPP patients are due primarily to a preexisting latent abnormal excitability of the muscle membrane, possibly genetic in origin.
Collapse
Affiliation(s)
- Kimiyoshi Arimura
- Department of Neurology and Geriatrics, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima 890-8520, Japan.
| | | | | | | | | |
Collapse
|
100
|
Nakajo K, Kubo Y. KCNE1 and KCNE3 stabilize and/or slow voltage sensing S4 segment of KCNQ1 channel. ACTA ACUST UNITED AC 2007; 130:269-81. [PMID: 17698596 PMCID: PMC2151641 DOI: 10.1085/jgp.200709805] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
KCNQ1 is a voltage-dependent K+ channel whose gating properties are dramatically altered by association with auxiliary KCNE proteins. For example, KCNE1, which is mainly expressed in heart and inner ear, markedly slows the activation kinetics of KCNQ1. Whether the voltage-sensing S4 segment moves differently in the presence of KCNE1 is not yet known, however. To address that question, we systematically introduced cysteine mutations, one at a time, into the first half of the S4 segment of human KCNQ1. A226C was found out as the most suited mutant for a methanethiosulfonate (MTS) accessibility analysis because it is located at the N-terminal end of S4 segment and its current was stable with repetitive stimuli in the absence of MTS reagent. MTS accessibility analysis revealed that the apparent second order rate constant for modification of the A226C mutant was state dependent, with faster modification during depolarization, and was 13 times slower in the presence of KCNE1 than in its absence. In the presence of KCNE3, on the other hand, the second order rate constant for modification was not state dependent, indicating that the C226 residue was always exposed to the extracellular milieu, even at the resting membrane potential. Taken together, these results suggest that KCNE1 stabilizes the S4 segment in the resting state and slows the rate of transition to the active state, while KCNE3 stabilizes the S4 segment in the active state. These results offer new insight into the mechanism of KCNQ1 channel modulation by KCNE1 and KCNE3.
Collapse
Affiliation(s)
- Koichi Nakajo
- Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi, 444-8585, Japan
| | | |
Collapse
|