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Fernandez-Ruocco J, Gallego M, Rodriguez-de-Yurre A, Zayas-Arrabal J, Echeazarra L, Alquiza A, Fernández-López V, Rodriguez-Robledo JM, Brito O, Schleier Y, Sepulveda M, Oshiyama NF, Vila-Petroff M, Bassani RA, Medei EH, Casis O. High Thyrotropin Is Critical for Cardiac Electrical Remodeling and Arrhythmia Vulnerability in Hypothyroidism. Thyroid 2019; 29:934-945. [PMID: 31084419 PMCID: PMC6648210 DOI: 10.1089/thy.2018.0709] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Background: Hypothyroidism, the most common endocrine disease, induces cardiac electrical remodeling that creates a substrate for ventricular arrhythmias. Recent studies report that high thyrotropin (TSH) levels are related to cardiac electrical abnormalities and increased mortality rates. The aim of the present work was to investigate the direct effects of TSH on the heart and its possible causative role in the increased incidence of arrhythmia in hypothyroidism. Methods: A new rat model of central hypothyroidism (low TSH levels) was created and characterized together with the classical propylthiouracil-induced primary hypothyroidism model (high TSH levels). Electrocardiograms were recorded in vivo, and ionic currents were recorded from isolated ventricular myocytes in vitro by the patch-clamp technique. Protein and mRNA were measured by Western blot and quantitative reverse transcription polymerase chain reaction in rat and human cardiac myocytes. Adult human action potentials were simulated in silico to incorporate the experimentally observed changes. Results: Both primary and central hypothyroidism models increased the L-type Ca2+ current (ICa-L) and decreased the ultra-rapid delayed rectifier K+ current (IKur) densities. However, only primary but not central hypothyroidism showed electrocardiographic repolarization abnormalities and increased ventricular arrhythmia incidence during caffeine/dobutamine challenge. These changes were paralleled by a decrease in the density of the transient outward K+ current (Ito) in cardiomyocytes from animals with primary but not central hypothyroidism. In vitro treatment with TSH for 24 hours enhanced isoproterenol-induced spontaneous activity in control ventricular cells and diminished Ito density in cardiomyocytes from control and central but not primary hypothyroidism animals. In human myocytes, TSH decreased the expression of KCND3 and KCNQ1, Ito, and the delayed rectifier K+ current (IKs) encoding proteins in a protein kinase A-dependent way. Transposing the changes produced by hypothyroidism and TSH to a computer model of human ventricular action potential resulted in enhanced occurrence of early afterdepolarizations and arrhythmia mostly in primary hypothyroidism, especially under β-adrenergic stimulation. Conclusions: The results suggest that suppression of repolarizing K+ currents by TSH underlies most of the electrical remodeling observed in hypothyroidism. This work demonstrates that the activation of the TSH-receptor/protein kinase A pathway in the heart is responsible for the cardiac electrical remodeling and arrhythmia generation seen in hypothyroidism.
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Affiliation(s)
- Julieta Fernandez-Ruocco
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janerio, Brazil
- Centro de Investigaciones Cardiovasculares, Conicet La Plata, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Buenos Aires, Argentina
| | - Monica Gallego
- Departamento de Fisiología, Facultad de Farmacia, Universidad del País Vasco UPV/EHU, Vitoria, Spain
| | - Ainhoa Rodriguez-de-Yurre
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janerio, Brazil
- Departamento de Fisiología, Facultad de Farmacia, Universidad del País Vasco UPV/EHU, Vitoria, Spain
| | - Julian Zayas-Arrabal
- Departamento de Fisiología, Facultad de Farmacia, Universidad del País Vasco UPV/EHU, Vitoria, Spain
| | - Leyre Echeazarra
- Departamento de Fisiología, Facultad de Farmacia, Universidad del País Vasco UPV/EHU, Vitoria, Spain
| | - Amaia Alquiza
- Departamento de Fisiología, Facultad de Farmacia, Universidad del País Vasco UPV/EHU, Vitoria, Spain
| | - Victor Fernández-López
- Departamento de Fisiología, Facultad de Farmacia, Universidad del País Vasco UPV/EHU, Vitoria, Spain
| | - Juan M. Rodriguez-Robledo
- Departamento de Fisiología, Facultad de Farmacia, Universidad del País Vasco UPV/EHU, Vitoria, Spain
| | - Oscar Brito
- National Institute of Cardiology (INC), Rio de Janeiro, Brazil
| | - Ygor Schleier
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janerio, Brazil
| | - Marisa Sepulveda
- Centro de Investigaciones Cardiovasculares, Conicet La Plata, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Buenos Aires, Argentina
| | | | - Martin Vila-Petroff
- Centro de Investigaciones Cardiovasculares, Conicet La Plata, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Buenos Aires, Argentina
| | - Rosana A. Bassani
- Center for Biomedical Engineering, University of Campinas, Campinas, Brazil
| | - Emiliano H. Medei
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janerio, Brazil
| | - Oscar Casis
- Departamento de Fisiología, Facultad de Farmacia, Universidad del País Vasco UPV/EHU, Vitoria, Spain
- Address correspondence to: Oscar Casis, MD, PhD, Departamento de Fisiología, Facultad de Farmacia, Universidad del País Vasco, Paseo de la Universidad 7, 01006 Vitoria-Gasteiz, Spain
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Abstract
OBJECTIVE Increased faecal butyrate levels have been reported in irritable bowel syndrome. Rectal instillation of sodium butyrate (NaB) increases visceral sensitivity in rats by an unknown mechanism. We seek to examine the signal transduction pathways responsible for the enhanced neuronal excitability in the dorsal root ganglion (DRG) following NaB enemas and demonstrate that this is responsible for the colonic hypersensitivity reported in this animal model. DESIGN Colorectal distention (CRD) studies were performed in rats treated with NaB rectal instillation with/without intrathecal or intravenous administration of mitogen-activated protein (MAP) kinase kinase inhibitor U0126. Western blot analysis and immunocytochemistry studies elucidated intracellular signalling pathways that modulate IA. Patch-clamp recordings were performed on isolated DRG neurons treated with NaB, with/without U0126. RESULTS Visceromotor responses (VMR) were markedly enhanced in NaB-treated rats. Western blot analysis of DRG neurons from NaB-treated rats showed a 2.2-fold increase in phosphorylated ERK1/2 (pEKR1/2) and 1.9-fold increase in phosphorylated voltage-gated potassium channel subunit 4.2 (pKv4.2). Intrathecal or intravenous administration of U0126 reduced VMR to CRD in NaB-treated rats and prevented increases in pERK1/2 and pKv4.2. Patch-clamp recordings of isolated DRG neurons showed that NaB caused a reduction in IA to 48.9%±1.4% of control and an increase in neuronal excitability, accompanied by a twofold increase in pERK1/2 and pKv4.2. Concurrent U0126 administration prevented these changes. CONCLUSIONS Visceral hypersensitivity induced by colonic NaB treatment is mediated by activation of the MAP kinase-ERK1/2 pathway, which phosphorylates Kv4.2. This results in a reduction in IA and an enhancement of DRG neuronal excitability.
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Affiliation(s)
- Dabo Xu
- Gastroenterology Research Unit, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan, USA
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3
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Lundby A, Jespersen T, Schmitt N, Grunnet M, Olesen SP, Cordeiro JM, Calloe K. Effect of the I(to) activator NS5806 on cloned K(V)4 channels depends on the accessory protein KChIP2. Br J Pharmacol 2010; 160:2028-44. [PMID: 20649599 PMCID: PMC2958647 DOI: 10.1111/j.1476-5381.2010.00859.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2009] [Revised: 02/09/2010] [Accepted: 03/22/2010] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND AND PURPOSE The compound NS5806 increases the transient outward current (I(to)) in canine ventricular cardiomyocytes and slows current decay. In human and canine ventricle, I(to) is thought to be mediated by K(V)4.3 and various ancillary proteins, yet, the exact subunit composition of I(to) channels is still debated. Here we characterize the effect of NS5806 on heterologously expressed putative I(to) channel subunits and other potassium channels. EXPERIMENTAL APPROACH Cloned K(V)4 channels were co-expressed with KChIP2, DPP6, DPP10, KCNE2, KCNE3 and K(V)1.4 in Xenopus laevis oocytes or CHO-K1 cells. KEY RESULTS NS5806 increased K(V)4.3/KChIP2 peak current amplitudes with an EC(50) of 5.3 +/- 1.5microM and significantly slowed current decay. KCNE2, KCNE3, DPP6 and DPP10 modulated K(V)4.3 currents and the response to NS5806, but current decay was slowed only in complexes containing KChIP2. The effect of NS5806 on K(V)4.2 was similar to that on K(V)4.3, and current decay was only slowed in presence of KChIP2. However, for K(V)4.1, the slowing of current decay by NS5806 was independent of KChIP2. K(V)1.4 was strongly inhibited by 10 microM NS5806 and K(V)1.5 was inhibited to a smaller extent. Effects of NS5806 on kinetics of currents generated by K(V)4.3/KChIP2/DPP6 with K(V)1.4 in oocytes could reproduce those on cardiac I(to) in canine ventricular myocytes. K(V)7.1, K(V)11.1 and K(ir)2 currents were unaffected by NS5806. CONCLUSION AND IMPLICATIONS NS5806 modulated K(V)4 channel gating depending on the presence of KChIP2, suggesting that NS5806 can potentially be used to address the molecular composition as well as the physiological role of cardiac I(to).
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Affiliation(s)
- A Lundby
- The Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
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4
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Yuan C, Liao Z, Zeng X, Dai L, Kuang F, Liang S. Jingzhaotoxin-XII, a gating modifier specific for Kv4.1 channels. Toxicon 2007; 50:646-52. [PMID: 17631373 DOI: 10.1016/j.toxicon.2007.05.009] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2007] [Revised: 05/15/2007] [Accepted: 05/29/2007] [Indexed: 01/17/2023]
Abstract
Jingzhaotoxin-XII (JZTX-XII), a 29-residue polypeptide, was purified from the venom of the Chinese tarantula Chilobrachys jingzhao. Electrophysiological recordings carried out in Xenopus laevis oocytes showed that JZTX-XII is specific for Kv4.1 channels, with the IC50 value of 0.363 microM. It interacts with the channels by modifying the gating behavior. JZTX-XII shares 80% sequence identity with phrixotoxin1, a potent inhibitor for Kv4.2 and Kv4.3 channels. Structure analysis indicates that the difference of the charge distribution in the interactive surface perhaps influences the specific pharmacology of the toxins. JZTX-XII should be a valuable tool for the investigation of the Kv4.1 channels.
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Affiliation(s)
- Chunhua Yuan
- Key Laboratory of Protein Chemistry and Developmental Biology of the Ministry of Education, Life Science College, Hunan Normal University, Changsha 410081, PR China
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5
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Fu XW, Nurse C, Cutz E. Characterization of slowly inactivating KV{alpha} current in rabbit pulmonary neuroepithelial bodies: effects of hypoxia and nicotine. Am J Physiol Lung Cell Mol Physiol 2007; 293:L892-902. [PMID: 17644754 DOI: 10.1152/ajplung.00098.2007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Pulmonary neuroepithelial bodies (NEB) form innervated cell clusters that express voltage-activated currents and function as airway O(2) sensors. We investigated A-type K(+) currents in NEB cells using neonatal rabbit lung slice preparation. The whole cell K(+) current was slowly inactivating with activation threshold of approximately -30 mV. This current was blocked approximately 27% by blood-depressing substance I (BDS-I; 3 microM), a selective blocker of Kv3.4 subunit, and reduced approximately 20% by tetraethylammonium (TEA; 100 microM). The BDS-I-sensitive component had an average peak value of 189 +/- 14 pA and showed fast inactivation kinetics that could be fitted by one-component exponential function with a time constant of (tau1) 77 +/- 10 ms. This Kv slowly inactivating current was also blocked by heteropodatoxin-2 (HpTx-2; 0.2 microM), a blocker of Kv4 subunit. The HpTx-2-sensitive current had an average peak value of 234 +/- 23 pA with a time constant (tau) 82 +/- 11 ms. Hypoxia (Po(2) = 15-20 mmHg) inhibited the slowly inactivating K(+) current by approximately 47%, during voltage steps from -30 to +30 mV, and no further inhibition occurred when TEA was combined with hypoxia. Nicotine at concentrations of 50 and 100 microM suppressed the slowly inactivating K(+) current by approximately 24 and approximately 40%, respectively. This suppression was not reversed by mecamylamine suggesting a direct effect of nicotine on these K(+) channels. In situ hybridization experiments detected expression of mRNAs for Kv3.4 and Kv4.3 subunits, while double-label immunofluorescence confirmed membrane localization of respective channel proteins in NEB cells. These studies suggest that the hypoxia-sensitive current in NEB cells is carried by slowly inactivating A-type K(+) channels, which underlie their oxygen-sensitive potassium currents, and that exposure to nicotine may directly affect their function, contributing to smoking-related lung disease.
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Affiliation(s)
- Xiao Wen Fu
- Division of Pathology, Department of Pediatric Laboratory Medicine, The Research Institute, The Hospital for Sick Children and University of Toronto, Toronto, Ontario M5G 1X8, Canada
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6
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Farkas I, Varju P, Liposits Z. Estrogen modulates potassium currents and expression of the Kv4.2 subunit in GT1-7 cells☆. Neurochem Int 2007; 50:619-27. [PMID: 17258352 DOI: 10.1016/j.neuint.2006.12.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2006] [Revised: 11/28/2006] [Accepted: 12/05/2006] [Indexed: 10/23/2022]
Abstract
The proper maintenance of reproduction requires the pulsatile secretion of gonadotropin-releasing hormone (GnRH), which is ensured by synchronized periodic firing of multiple GnRH neurons. Both hormone secretion and electrophysiological properties of GnRH cells are influenced by estrogen. The impact of 17beta-estradiol treatment on the function of voltage gated A- and K-type potassium channels, known modulators of firing rate, was therefore examined in our experiments using immortalized GnRH-producing GT1-7 neurons. Whole cell patch clamp recordings showed the absence of the A-type current in GT1-7 cells cultured in estrogen-free medium and after 8h 17beta-estradiol treatment. Exposure of the cells to 17beta-estradiol for 24 and 48 h, respectively, resulted in the appearance of the A-type current. The induction of the A-type current by 17beta-estradiol was dose-related (50 pM to 15 nM range). In contrast, the K-type potassium current was apparent in the estrogen-free environment and 17beta-estradiol administration significantly decreased its amplitude. Co-administration of 17beta-estradiol and estrogen receptor blocker, Faslodex (ICI 182,780; 1 microM) abolished the occurrence of the A-type current. Real-time PCR data demonstrated that expression of the Kv4.2 subunit of the A-type channel was low at 0, 0.5, 2 and 8h, peaked at 24h and diminished at 48 h 17beta-estradiol treatment (15 nM). These data indicate that potassium channels of GT1-7 neurons are regulated by estrogen a mechanism that might contribute to modulation of firing rate and hormone secretion in GnRH neurons.
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Affiliation(s)
- Imre Farkas
- Laboratory of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Szigony u. 43, 1083 Budapest, Hungary.
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7
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Saygili E, Rana OR, Saygili E, Reuter H, Frank K, Schwinger RHG, Müller-Ehmsen J, Zobel C. Losartan prevents stretch-induced electrical remodeling in cultured atrial neonatal myocytes. Am J Physiol Heart Circ Physiol 2007; 292:H2898-905. [PMID: 17293496 DOI: 10.1152/ajpheart.00546.2006] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Atrial fibrillation (AF) is the most frequent arrhythmia found in clinical practice. In recent studies, a decrease in the development or recurrence of AF was found in hypertensive patients treated with angiotensin-converting enzyme inhibitors or angiotensin receptor-blocking agents. Hypertension is related to an increased wall tension in the atria, resulting in increased stretch of the individual myocyte, which is one of the major stimuli for the remodeling process. In the present study, we used a model of cultured atrial neonatal rat cardiomyocytes under conditions of stretch to provide insight into the mechanisms of the preventive effect of the angiotensin receptor-blocking agent losartan against AF on a molecular level. Stretch significantly increased protein-to-DNA ratio and atrial natriuretic factor mRNA expression, indicating hypertrophy. Expression of genes encoding for the inward rectifier K(+) current (I(K1)), Kir 2.1, and Kir 2.3, as well as the gene encoding for the ultrarapid delayed rectifier K(+) current (I(Kur)), Kv 1.5, was significantly increased. In contrast, mRNA expression of Kv 4.2 was significantly reduced in stretched myocytes. Alterations of gene expression correlated with the corresponding current densities: I(K1) and I(Kur) densities were significantly increased in stretched myocytes, whereas transient outward K(+) current (I(to)) density was reduced. These alterations resulted in a significant abbreviation of the action potential duration. Losartan (1 microM) prevented stretch-induced increases in the protein-to-DNA ratio and atrial natriuretic peptide mRNA expression in stretched myocytes. Concomitantly, losartan attenuated stretch-induced alterations in I(K1), I(Kur), and I(to) density and gene expression. This prevented the stretch-induced abbreviation of action potential duration. Prevention of stretch-induced electrical remodeling might contribute to the clinical effects of losartan against AF.
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MESH Headings
- Action Potentials/drug effects
- Angiotensin II Type 1 Receptor Blockers/pharmacology
- Angiotensin II Type 1 Receptor Blockers/therapeutic use
- Animals
- Animals, Newborn
- Antihypertensive Agents/pharmacology
- Antihypertensive Agents/therapeutic use
- Atrial Fibrillation/etiology
- Atrial Fibrillation/prevention & control
- Atrial Natriuretic Factor/genetics
- Atrial Natriuretic Factor/metabolism
- Cell Enlargement/drug effects
- Cell Shape/drug effects
- Cell Size/drug effects
- Cells, Cultured
- Gene Expression/drug effects
- Heart Atria/cytology
- Heart Atria/drug effects
- Heart Atria/metabolism
- Hypertension/complications
- Hypertension/drug therapy
- Kinetics
- Kv1.5 Potassium Channel/drug effects
- Kv1.5 Potassium Channel/metabolism
- Losartan/pharmacology
- Losartan/therapeutic use
- Mechanotransduction, Cellular/drug effects
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/metabolism
- Potassium/metabolism
- Potassium Channels, Inwardly Rectifying/drug effects
- Potassium Channels, Inwardly Rectifying/metabolism
- Potassium Channels, Voltage-Gated/drug effects
- Potassium Channels, Voltage-Gated/genetics
- Potassium Channels, Voltage-Gated/metabolism
- RNA, Messenger/metabolism
- Rats
- Shal Potassium Channels/drug effects
- Shal Potassium Channels/metabolism
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Affiliation(s)
- Erol Saygili
- Laboratory of Muscle Research and Molecular Cardiology, Department of Internal Medicine III, University of Cologne, Kerpenerstr. 62, 50924 Cologne, Germany
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8
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Abstract
Ca(+)-calmodulin (Ca(2+)-CaM)-dependent protein kinase II (Ca(2+)/CaMKII) is an important regulator of cardiac ion channels, and its inhibition may be an approach for treatment of ventricular arrhythmias. Using the two-electrode voltage-clamp technique, we investigated the role of W-7, an inhibitor of Ca(2+)-occupied CaM, and KN-93, an inhibitor of Ca(2+)/CaMKII, on the K(v)4.3 channel in Xenopus laevis oocytes. W-7 caused a voltage- and concentration-dependent decrease in peak current, with IC(50) of 92.4 muM. The block was voltage dependent, with an effective electrical distance of 0.18 +/- 0.05, and use dependence was observed, suggesting that a component of W-7 inhibition of K(v)4.3 current was due to open-channel block. W-7 made recovery from open-state inactivation a biexponential process, also suggesting open-channel block. We compared the effects of W-7 with those of KN-93 after washout of 500 muM BAPTA-AM. KN-93 reduced peak current without evidence of voltage or use dependence. Both W-7 and KN-93 accelerated all components of inactivation. We used wild-type and mutated K(v)4.3 channels with mutant CaMKII consensus phosphorylation sites to examine the effects of W-7 and KN-93. In contrast to W-7, KN-93 at 35 muM selectively accelerated open-state inactivation in the wild-type vs. the mutant channel. W-7 had a significantly greater effect on recovery from inactivation in wild-type than in mutant channels. We conclude that, at certain concentrations, KN-93 selectively inhibits Ca(2+)/CaMKII activity in Xenopus oocytes and that the effects of W-7 are mediated by direct interaction with the channel pore and inhibition of Ca(2+)-CaM, as well as a change in activity of Ca(2+)-CaM-dependent enzymes, including Ca(2+)/CaMKII.
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Affiliation(s)
- Yu-Jie Qu
- Department of Physiology and Biophysics, School of Medicine and Biomedical Sciences, University at Buffalo-State University of New York, 3435 Main Street, Buffalo, NY 14214, USA
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9
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Gong N, Bodi I, Zobel C, Schwartz A, Molkentin JD, Backx PH. Calcineurin increases cardiac transient outward K+ currents via transcriptional up-regulation of Kv4.2 channel subunits. J Biol Chem 2006; 281:38498-506. [PMID: 17060317 DOI: 10.1074/jbc.m607774200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Fast transient outward potassium currents (I(to,f)) are critical determinants of regional heterogeneity of cardiomyocyte repolarization as well as cardiomyocyte contractility. Additionally, I(to,f) densities are markedly down-regulated in cardiac hypertrophy and heart disease, conditions associated with activation of the serine/threonine phosphatase calcineurin (Cn). In this study, we investigated the regulation of I(to,f) expression by Cn in cultured neonatal rat ventricular myocytes (NRVMs) with and without alpha(1)-adrenoreceptor stimulation with phenylephrine (PE). Overexpression of constitutively active Cn in NRVMs induced hypertrophy and caused profound increases in I(to,f) density as well as Kv4.2 mRNA and protein expression and promoter activity, without affecting Kv4.3 or KChIP2 levels. The effects of Cn on hypertrophy, I(to,f), and Kv4.2 transcription were associated with NFAT activation and were abrogated by NFAT inhibition. Despite activating Cn and inducing hypertrophy in NRVMs, PE resulted in profound down-regulation of I(to,f) densities as well as Kv4.2, Kv4.3, and KChIP2 expression. Although hypertrophy and NFAT activation were inhibited by the Cn inhibitory peptide CAIN, I(to,f) and Kv4.2 expression were further reduced by CAIN, whereas Cn overexpression eliminated PE-induced reductions in I(to,f) and Kv4.2 expression without affecting Kv4.3 or KChIP2 levels. We conclude that Cn increases cardiac I(to,f) densities by positively regulating Kv4.2 gene transcription. Consistent with this conclusion, we found that I(to,f) was increased in myocytes isolated from young mice overexpressing Cn prior to the development of heart disease. This positive regulation of Kv4.2 transcription by Cn activation is expected to minimize the reductions in I(to,f) and Kv4.2 expression observed in hypertrophic cardiomyocytes.
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Affiliation(s)
- Nanling Gong
- Departments of Physiology and Medicine, Heart and Stroke/Richard Lewar Centre of Excellence, University Health Network, University of Toronto, 150 College Street, Toronto, Ontario M5S 3E2, Canada
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10
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Lauver A, Yuan LL, Jeromin A, Nadin BM, Rodríguez JJ, Davies HA, Stewart MG, Wu GY, Pfaffinger PJ. Manipulating Kv4.2 identifies a specific component of hippocampal pyramidal neuron A-current that depends upon Kv4.2 expression. J Neurochem 2006; 99:1207-23. [PMID: 17026528 PMCID: PMC3583589 DOI: 10.1111/j.1471-4159.2006.04185.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The somatodendritic A-current, I(SA), in hippocampal CA1 pyramidal neurons regulates the processing of synaptic inputs and the amplitude of back propagating action potentials into the dendritic tree, as well as the action potential firing properties at the soma. In this study, we have used RNA interference and over-expression to show that expression of the Kv4.2 gene specifically regulates the I(SA) component of A-current in these neurons. In dissociated hippocampal pyramidal neuron cultures, or organotypic cultured CA1 pyramidal neurons, the expression level of Kv4.2 is such that the I(SA) channels are maintained in the population at a peak conductance of approximately 950 pS/pF. Suppression of Kv4.2 transcripts in hippocampal pyramidal neurons using an RNA interference vector suppresses I(SA) current by 60% in 2 days, similar to the effect of expressing dominant-negative Kv4 channel constructs. Increasing the expression of Kv4.2 in these neurons increases the level of I(SA) to 170% of the normal set point without altering the biophysical properties. Our results establish a specific role for native Kv4.2 transcripts in forming and maintaining I(SA) current at characteristic levels in hippocampal pyramidal neurons.
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Affiliation(s)
- Aaron Lauver
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, USA
| | - Li-Lian Yuan
- Department of Neuroscience, University of Minnesota, Minneapolis, Minneapolis, USA
| | - Andreas Jeromin
- Center for Learning and Memory, University of Texas at Austin, Texas, USA
| | - Brian M. Nadin
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, USA
| | - José J. Rodríguez
- Department of Biological Sciences, The Open University, Milton Keynes, UK
| | - Heather A. Davies
- Department of Biological Sciences, The Open University, Milton Keynes, UK
| | - Michael G. Stewart
- Department of Biological Sciences, The Open University, Milton Keynes, UK
| | - Gang-Yi Wu
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas, USA
| | - Paul J. Pfaffinger
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, USA
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11
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Yeung SYM, Ohya S, Sergeant GP, Pucovský V, Greenwood IA. Pharmacological and molecular evidence for the involvement of Kv4.3 in ultra-fast activating K+ currents in murine portal vein myocytes. Br J Pharmacol 2006; 149:676-86. [PMID: 17016508 PMCID: PMC2014655 DOI: 10.1038/sj.bjp.0706903] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
BACKGROUND AND PURPOSE The aim of this study was to determine the molecular identity of a transient K+ current (termed IUF) in mouse portal vein myocytes using pharmacological and molecular tools. EXPERIMENTAL APPROACH Whole cell currents were recorded using the ruptured patch con from either acutely dispersed single smooth muscle cells from the murine portal vein or human embryonic kidney cells. Reverse transcriptase polymerase reaction (RT-PCR) experiments were undertaken on RNA isolated from mouse portal vein using primers specific for various voltage-dependent K+ channels, auxillary subunits and calcium-binding proteins. Immunocytochemistry was undertaken using an antibody specific for Kv4.3. KEY RESULTS IUF had a mean amplitude at +40 mV of 558 +/- 50 pA (n = 32) with a mean time to peak at +40 mV of approximately 4 ms. IUF activated and inactivated with a half maximal voltage of -12 +/- 2 mV and -85 +/- 2 mV, respectively. IUF was relatively resistant to 4-aminopyridine (5 mM produced 30 +/- 6 % block at +20 mV) but was inhibited effectively by flecainide (IC50 value was 100 nM) and phrixotoxin II. This pharmacological profile is consistent with IUF being comprised of Kv4.x proteins and this is supported by the results from the quantitative PCR and immunocytochemical experiments. CONCLUSIONS AND IMPLICATIONS These data represent a rigorous investigation of the molecular basis of vascular transient K+ currents and implicates Kv4.3 as a major component of the channel complex.
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Affiliation(s)
- S Y M Yeung
- Division of Basic Medical Sciences, Ion Channels and Cell Signalling Research Centre, St George's, University of London London, UK
| | - S Ohya
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City UniversityJapan
| | - G P Sergeant
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk Co Louth, Ireland
| | - V Pucovský
- Division of Basic Medical Sciences, Ion Channels and Cell Signalling Research Centre, St George's, University of London London, UK
| | - I A Greenwood
- Division of Basic Medical Sciences, Ion Channels and Cell Signalling Research Centre, St George's, University of London London, UK
- Author for correspondence:
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12
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Colinas O, Gallego M, Setién R, López-López JR, Pérez-García MT, Casis O. Differential modulation of Kv4.2 and Kv4.3 channels by calmodulin-dependent protein kinase II in rat cardiac myocytes. Am J Physiol Heart Circ Physiol 2006; 291:H1978-87. [PMID: 16648177 DOI: 10.1152/ajpheart.01373.2005] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In this work we have combined biochemical and electrophysiological approaches to explore the modulation of rat ventricular transient outward K+ current ( Ito) by calmodulin kinase II (CaMKII). Intracellular application of CaMKII inhibitors KN93, calmidazolium, and autocamtide-2-related inhibitory peptide II (ARIP-II) accelerated the inactivation of Ito, even at low [Ca2+]. In the same conditions, CaMKII coimmunoprecipitated with Kv4.3 channels, suggesting that phosphorylation of Kv4.3 channels modulate inactivation of Ito. Because channels underlying Ito are heteromultimers of Kv4.2 and Kv4.3, we have explored the effect of CaMKII on human embryonic kidney (HEK) cells transfected with either of those Kvα-subunits. Whereas Kv4.3 inactivated faster upon inhibition of CaMKII, Kv4.2 inactivation was insensitive to CaMKII inhibitors. However, Kv4.2 inactivation became slower when high Ca2+ was used in the pipette or when intracellular [Ca2+] ([Ca2+]i) was transiently increased. This effect was inhibited by KN93, and Western blot analysis demonstrated Ca2+-dependent phosphorylation of Kv4.2 channels. On the contrary, CaMKII coimmunoprecipitated with Kv4.3 channels without a previous Ca2+ increase, and the association was inhibited by KN93. These results suggest that both channels underlying Ito are substrates of CaMKII, although with different sensitivities; Kv4.2 remain unphosphorylated unless [Ca2+]i increases, whereas Kv4.3 are phosphorylated at rest. In addition to the functional impact that phosphorylation of Kv4 channels could cause on the shape of action potential, association of CaMKII with Kv4.3 provides a new role of Kv4.3 subunits as molecular scaffolds for concentrating CaMKII in the membrane, allowing Ca2+-dependent modulation by this enzyme of the associated Kv4.2 channels.
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Affiliation(s)
- Olaia Colinas
- Departamento de Bioquímica y Biología Molecular y Fisiología, Edificio IBGM, Universidad de Valladolid, C/ Sanz y Forés s/n, 47003 Valladolid, Spain
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13
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Vacher H, Diochot S, Bougis PE, Martin-Eauclaire MF, Mourre C. Kv4 channels sensitive to BmTX3 in rat nervous system: autoradiographic analysis of their distribution during brain ontogenesis. Eur J Neurosci 2006; 24:1325-40. [PMID: 16987219 DOI: 10.1111/j.1460-9568.2006.05020.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The binding site distribution of sBmTX3, a chemically synthesized toxin originally purified from the venom of the scorpion Buthus martensi, was investigated in adult and developing rat brain, using patch-clamp experiments and quantitative autoradiography. The molecular basis of these sBmTX3 sites was analysed by electrophysiology on transient Kv currents recorded in mammalian transfected cells. The rapidly activating and inactivating Kv4.1 current was inhibited by sBmTX3 (IC50, 105 nM). The inhibition was less effective on Kv4.2 and Kv4.3 channels and the toxin did not affect other transient currents such as Kv1.4 and Kv3.4. The distribution of the 125I-sBmTX3 binding sites was heterogeneous, with a 113-fold difference between the highest and the lowest densities in adult rat brain. The site density was particularly important in the caudate-putamen and accumbens nucleus, thalamus, hippocampal formation and cerebellum. The affinity of sBmTX3 remained constant during brain ontogenesis. The level of sBmTX3 binding sites was very low in prenatal and postnatal stages to postnatal day (P)12 but drastically increased from P15 in the major part of the studied structures except in the CA3 hippocampal field where the density was very high from P6. Thus, the distribution of sBmTX3 binding sites in rat brain and its electrophysiological characteristics suggest that sBmTX3 specifically binds to the Kv4 subfamily of K channels.
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Affiliation(s)
- Hélène Vacher
- CNRS, UMR 6149, Neurobiologie des Processus Mnésiques, Université de Provence, Pôle 3C, Centre St Charles, 3 Place Victor Hugo, 13331 Marseille cedex 03, France
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14
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van der Heyden MAG, Wijnhoven TJM, Opthof T. Molecular aspects of adrenergic modulation of the transient outward current. Cardiovasc Res 2006; 71:430-42. [PMID: 16762331 DOI: 10.1016/j.cardiores.2006.04.012] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2005] [Revised: 04/05/2006] [Accepted: 04/20/2006] [Indexed: 11/27/2022] Open
Abstract
Transient outward channels have a different impact on action potential configuration in small mammals compared to large mammals. Small mammals depend primarily on Ito1 for repolarization, while in larger animals Ito1 only indirectly determines action potential duration by setting the level of the plateau. Transient outward channel expression and distribution also differ between animal species. Nevertheless, the primary protein sequence of the underlying Kv1.4, Kv4.2 and Kv4.3 alpha1-subunits displays remarkably high levels of amino acid identity. Transient outward channels are subject to alpha- and beta-adrenergic regulation, mainly decreasing Ito1. However, adrenergic stimulation is also an important determinant of transient outward channel downregulation in cardiac disease. Adrenergic stimulation of PKA as well as PKC leads to an inhibition of Ito1, which has been correlated with phosphorylation of the Kv1.4, Kv4.2 and Kv4.3 alpha1-subunits. Calmodulin-dependent kinase II, on the other hand, has been shown to be involved in an increase of Ito1. Comparison of Kv1.4, Kv4.2 and Kv4.3 primary amino acid sequences demonstrates a strong conservation of (potential) phosphorylation sites between different species, despite the fact that Ito1 has a different effect on action potential configuration in mammalian species.
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15
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Bett GCL, Morales MJ, Strauss HC, Rasmusson RL. KChIP2b modulates the affinity and use-dependent block of Kv4.3 by nifedipine. Biochem Biophys Res Commun 2006; 340:1167-77. [PMID: 16414350 DOI: 10.1016/j.bbrc.2005.12.135] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2005] [Accepted: 12/20/2005] [Indexed: 10/25/2022]
Abstract
Rapidly activating Kv4 voltage-gated ion channels are found in heart, brain, and diverse other tissues including colon and uterus. Kv4.3 can co-assemble with KChIP ancillary subunits, which modify kinetic behavior. We examined the affinity and use dependence of nifedipine block on Kv4.3 and its modulation by KChIP2b. Nifedipine (150 microM) reduced peak Kv4.3 current approximately 50%, but Kv4.3/KChIP2b current only approximately 27%. Nifedipine produced a very rapid component of open channel block in both Kv4.3 and Kv4.3/KChIP2b. However, recovery from the blocked/inactivated state was strongly sensitive to KChIP2b. Kv4.3 Thalf,recovery was slowed significantly by nifedipine (120.0+/-12.4 ms vs. 213.1+/-18.2 ms), whereas KChIP2b eliminated nifedipine's effect on recovery: Kv4.3/KChIP2b Thalf,recovery was 45.3+/-7.2 ms (control) and 47.8+/-8.2 ms (nifedipine). Consequently, Kv4.3 exhibited use-dependent nifedipine block in response to a series of depolarizing pulses which was abolished by KChIP2b. KChIPs alter drug affinity and use dependence of Kv4.3.
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Affiliation(s)
- Glenna C L Bett
- Center for Cellular and Systems Electrophysiology, Department of Gynecology and Obstetrics, School of Medicine and Biomedical Sciences, 124 Sherman Hall, State University of New York at Buffalo, Buffalo, NY 14214-300, USA
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16
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Kawada H, Niwano S, Niwano H, Yumoto Y, Wakisaka Y, Yuge M, Kawahara K, Izumi T. Tumor Necrosis Factor-.ALPHA. Downregulates the Voltage Gated Outward K+ Current in Cultured Neonatal Rat Cardiomyocytes A Possible Cause of Electrical Remodeling in Diseased Hearts. Circ J 2006; 70:605-9. [PMID: 16636498 DOI: 10.1253/circj.70.605] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND Inflammatory cytokines have been reported to contribute to the progression of cardiac remodeling in various heart diseases and a remarkable prolongation of the monophasic action potential duration and reductions in the expression of Kv4.2 and K+ channel-interacting protein-2 (KChIP-2) in a rat autoimmune myocarditis model have been documented. In this study, the effect of tumor necrosis factor-alpha (TNF-alpha) on cultured cardiomyocytes was evaluated, focusing on the change in the voltage-gated outward K+ current and expression of related molecules. METHODS AND RESULTS Cardiomyocytes isolated from 1-day-old Lewis rats were cultured for 72 h and treated with TNF-alpha (50 ng/ml) for an additional 48 h. The myocytes treated with TNF-alpha showed a 22% reduction in the peak K+ current, which consisted of a transient outward K+ current (Ito) and 1.4-fold enhancement of the cell-capacitance in comparison with the control. Among the cardiac ion channel related molecules evaluated in this study, Kv4.2 and KChIP-2 mRNA exhibited remarkable reductions (p < 0.05). CONCLUSIONS Treatment with TNF-alpha induced reductions in Ito as well as cellular hypertrophy in neonatal cultured myocytes, which indicates that TNF-alpha might play a role in promoting electrical remodeling of cardiomyocytes under inflammatory conditions.
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MESH Headings
- Action Potentials
- Animals
- Animals, Newborn
- Cells, Cultured
- Disease Models, Animal
- Down-Regulation/drug effects
- Down-Regulation/genetics
- Heart Diseases/pathology
- Heart Diseases/physiopathology
- Hypertrophy/chemically induced
- Hypertrophy/pathology
- Kv Channel-Interacting Proteins/drug effects
- Kv Channel-Interacting Proteins/genetics
- Myocarditis/immunology
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/metabolism
- Myocytes, Cardiac/pathology
- Potassium/metabolism
- Potassium Channels, Voltage-Gated/drug effects
- Potassium Channels, Voltage-Gated/genetics
- RNA, Messenger/analysis
- Rats
- Rats, Inbred Lew
- Shal Potassium Channels/drug effects
- Shal Potassium Channels/genetics
- Tumor Necrosis Factor-alpha/pharmacology
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Affiliation(s)
- Hideaki Kawada
- Department of Angio-cardiology, Kitasato University School of Medicine, Sagamihara, Japan
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17
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Ognjenovic M, Perry L. American Chemical Society 230th National Meeting. Neurological disorders. IDrugs 2005; 8:887-9. [PMID: 16254777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
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Abstract
Although angiotensin II inhibits transient outward K+ currents (I(A)s) in subfornical organ neurones, there is no evidence concerning which Kv channels are involved. We investigated I(A)-generating Kv channels in dissociated rat subfornical organ neurones, using molecular, electrophysiological and pharmacological techniques, and studied the effects of angiotensin II. Conventional RT-PCR showed the presence of mRNAs for channels of the Kv3.4, Kv1.4 and Kv4 families, which are capable of generating I(A)s. Tetraethylammonium at 1 mm, which blocks Kv3 channel-derived currents, and blood-depressing substance-I, a Kv3.4-specific blocker, at 2 microm suppressed the I(A)-like component of whole-cell outward currents in some neurones. 4-Aminopyridine at 5 mm inhibited I(A)s in the presence of tetraethylammonium at 1 mm. Cd2+ at 300 microm shifted the activation and inactivation curves of the 4-aminopyridine-sensitive and tetraethylammonium-resistant I(A)s positively. The tetraethylammonium-resistant I(A)s showed fast and slow components during the process of recovery from inactivation, but the slow component was not seen in all neurones. The time constant of the fast recovery component was less than 200 ms, while that of the slow recovery component was around 1 s. Using single-cell RT-PCR, mRNAs for Kv4.2 and Kv4.3L were detected frequently, but those for Kv1.4 and Kv3.4 were seen only rarely. Angiotensin II at 30 nm inhibited the fast recovery component of tetraethylammonium-resistant I(A)s in many neurones. These results suggest that the fast recovery component of the tetraethylammonium-resistant I(A) in subfornical organ neurones depends upon Kv4, and that it can be modulated by angiotensin II.
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Affiliation(s)
- Kentaro Ono
- Department of Biosciences, Kyushu Dental College, 2-6-1 Manazuru, Kokurakitaku, Kitakyushu, 803-8580, Japan
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