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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.
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52
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Putney JW. The physiological function of store-operated calcium entry. Neurochem Res 2011; 36:1157-65. [PMID: 21234676 DOI: 10.1007/s11064-010-0383-0] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/20/2010] [Indexed: 01/22/2023]
Abstract
Store-operated Ca(2+) entry is a process whereby the depletion of intracellular Ca(2+) stores signals the opening of plasma membrane Ca(2+) channels. It has long been thought that the main function of store-operated Ca(2+) entry was the replenishment of intracellular Ca(2+) stores following their discharge during intracellular Ca(2+) signaling. Recent results, however, suggest that the primary function of these channels may be to provide direct Ca(2+) signals to recipients localized to spatially restricted areas close to the sites of Ca(2+) entry in order to initiate specific signaling pathways.
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Affiliation(s)
- James W Putney
- National Institute of Environmental Health Sciences-NIH, Department of Health and Human Services, PO Box 12233, Research Triangle Park, NC 27709, USA.
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Chen L, Lai C, Lai J, Tian C. Expression, purification, detergent screening and solution NMR backbone assignment of the human potassium channel accessory subunit MiRP1. Protein Expr Purif 2010; 76:205-10. [PMID: 21087668 DOI: 10.1016/j.pep.2010.11.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Revised: 10/31/2010] [Accepted: 11/03/2010] [Indexed: 10/18/2022]
Abstract
MiRP1 (MinK related protein 1) is a membrane protein in the KCNE family. It can associate with and modulate various voltage gated potassium channels. Mutations in human MiRP1 have been found to cause many congenital and acquired long QT syndromes, which are potentially life-threatening cardiac arrhythmias. Here, human MiRP1 was over-expressed in Escherichia coli, purified and eluted into different detergents. Two dimensional (1)H-(15)N correlated solution nuclear magnetic resonance (NMR) spectra of the human MiRP1 in four different detergent micelles indicated that high resolution solution NMR spectrum can be obtained for human MiRP1 in detergent lyso-myristoylphosphatidylglycerol (LMPG). Circular dichroism (CD) spectroscopy of human MiRP1 indicated a high content of alpha-helical secondary structure in LMPG. Backbone assignments of most MiRP1 residues were achieved through a series of triple resonance NMR experiments. Secondary structure analysis based on backbone chemical shifts showed several stretches of alpha-helices along the primary sequence of MiRP1 in LMPG.
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Affiliation(s)
- Liu Chen
- Hefei National Laboratory for Physical Science at Microscale and School of Life Science, University of Science and Technology of China, Hefei, Anhui, PR China
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54
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Abstract
Prenatal exposure to toxicants, such as maternal smoking, may impair cardiovascular autonomic maturation in infants. We recently showed that exposure of pregnant rats to a mild concentration of carbon monoxide (CO), a component of cigarette smoke, delays postnatal electrophysiological maturation of ventricular myocytes from newborns rats, likely predisposing to life-threatening arrhythmias. To get a comprehensive view of developmental molecular abnormalities induced, at cardiac level, by prenatal CO exposure, we used microarray analysis approach on the rat heart at 4, 7 and 20 days postnatal life. The relationship between molecular and functional alterations was investigated by assessing the ventricular expression of f-current, an electrophysiological marker of immature cardiac phenotype. Rats were prenatally exposed to 0 (CTR) or 150 p.p.m. CO and mRNA obtained from ventricular samples. Differential analysis and biological pathway analysis of microarray data were performed by using Newton's approach and the GENMAPP/MAPPFinder, respectively. The real-time RT-PCR reactions were performed by TaqMan probe-based chemistry. Freshly isolated patch-clamped ventricular cardiomyocytes were used to measure I(f). Genes and pathways controlling cell cycle and excitation-contraction coupling were significantly modified in CO-exposed rats. The higher effect was observed in cardiomyocytes harvested from 7-day-old rats, in which mRNA expression for crucial sarcomeric proteins (myosin and actin subunits, troponin I), transporters (Ca(2+) transporting ATPase) and enzymes (aldolase) were significantly downregulated. Accordingly, the molecular and functional expression of f-channels, which represents a marker of fetal ventricular phenotype, was transiently greater in CO-exposed rats (+200%) than in control ones. In conclusion, our study provides new insights into the molecular and functional mechanisms underlying cardiac maturation and its impairment by prenatal exposure to toxic components of smoking, such as CO.
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55
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Levy DI, Cepaitis E, Wanderling S, Toth PT, Archer SL, Goldstein SAN. The membrane protein MiRP3 regulates Kv4.2 channels in a KChIP-dependent manner. J Physiol 2010; 588:2657-68. [PMID: 20498229 DOI: 10.1113/jphysiol.2010.191395] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
MiRP3, the single-span membrane protein encoded by KCNE4, is localized by immunofluorescence microscopy to the transverse tubules of murine cardiac myocytes. MiRP3 is found to co-localize with Kv4.2 subunits that contribute to cardiac transient outward potassium currents (I(to)). Whole-cell, voltage-clamp recordings of human MiRP3 and Kv4.2 expressed in a clonal cell line (tsA201) reveal MiRP3 to modulate Kv4.2 current activation, inactivation and recovery from inactivation. MiRP3 shifts the half-maximal voltage for activation (V(1/2)) approximately 20 mV and slows time to peak approximately 100%. In addition, MiRP3 slows inactivation approximately 100%, speeds recovery from inactivation approximately 30%, and enhances restored currents so they 'overshoot' baseline levels. The cytoplasmic accessory subunit KChIP2 also assembles with Kv4.2 in tsA201 cells to increase peak current, shift V(1/2) approximately 5 mV, slow time to peak approximately 10%, slow inactivation approximately 100%, and speed recovery from inactivation approximately 250% without overshoot. Simultaneous expression of all three subunits yields a biophysical profile unlike either accessory subunit alone, abolishes MiRP3-induced overshoot, and allows biochemical isolation of the ternary complex. Thus, regional heterogeneity in cardiac expression of MiRP3, Kv4.2 and KChIP2 in health and disease may establish the local attributes and magnitude of cardiac I(to).
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Affiliation(s)
- Daniel I Levy
- Department of Medicine, Biological Sciences Division, Pritzker School of Medicine, University of Chicago, Chicago, IL 60637, USA.
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56
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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.
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Affiliation(s)
- Olaf Pongs
- Institut für Neurale Signalverarbeitung, Zentrum für Molekulare Neurobiologie Hamburg, Universitätsklinikum Hamburg-Eppendorf, Universität Hamburg, Hamburg, Germany.
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57
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Cardiac Ito, KCNE2, and Brugada syndrome: Promiscuous subunit interactions, or what happens in HEK cells stays in HEK cells? Heart Rhythm 2010; 7:206-7. [DOI: 10.1016/j.hrthm.2009.10.029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/23/2009] [Indexed: 11/24/2022]
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58
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Thollon C, Vilaine JP. I(f) inhibition in cardiovascular diseases. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2010; 59:53-92. [PMID: 20933199 DOI: 10.1016/s1054-3589(10)59003-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Heart rate (HR) is determined by the pacemaker activity of cells from the sinoatrial node (SAN), located in the right atria. Spontaneous electrical activity of SAN cells results from a diastolic depolarization (DD). Despite controversy in the exact contribution of funny current (I(f)) in pacemaking, it is a major contributor of DD. I(f) is an inward Na(+)/K(+) current, activated upon hyperpolarization and directly modulated by cyclic adenosine monophosphate. The f-proteins are hyperpolarization-activated cyclic nucleotide-gated channels, HCN4 being the main isoform of SAN. Ivabradine (IVA) decreases DD and inhibits I(f) in a use-dependent manner. Under normal conditions IVA selectively reduces HR and limits exercise-induced tachycardia, in animals and young volunteers. Reduction in HR with IVA both decreases myocardial oxygen consumption and increases its supply due to prolongation of diastolic perfusion time. In animal models and in human with coronary artery disease (CAD), IVA has anti-anginal and anti-ischemic efficacy, equipotent to classical treatments, β-blockers, or calcium channel blockers. As expected from its selectivity for I(f), the drug is safe and well tolerated with minor visual side effects. As a consequence, IVA is the first inhibitor of I(f) approved for the treatment of stable angina. Available clinical data indicate that IVA could improve the management of stable angina in all patients including those treated with β-blockers. As chronic elevation of resting HR is an independent predictor of mortality, pure HR reduction by inhibition of I(f) could, beyond the control of anti-anginal symptoms, improve the prognosis of CAD and heart failure; this therapeutic potential is currently under evaluation with IVA.
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Affiliation(s)
- Catherine Thollon
- Cardiovascular Department, Institut de Recherches Servier, Suresnes, France
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59
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Earley S, Brayden J, Reading S. Functional Significance of Transient Receptor Potential Channels in Vascular Function. ACTA ACUST UNITED AC 2009. [DOI: 10.1201/9781420005844.ch26] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
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60
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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.
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Affiliation(s)
- Paula L Hedley
- Department of Clinical Biochemistry and Immunology, Statens Serum Institut, Copenhagen, Denmark
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61
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Wu J, Shimizu W, Ding WG, Ohno S, Toyoda F, Itoh H, Zang WJ, Miyamoto Y, Kamakura S, Matsuura H, Nademanee K, Brugada J, Brugada P, Brugada R, Vatta M, Towbin JA, Antzelevitch C, Horie M. KCNE2 modulation of Kv4.3 current and its potential role in fatal rhythm disorders. Heart Rhythm 2009; 7:199-205. [PMID: 20042375 DOI: 10.1016/j.hrthm.2009.10.012] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/20/2009] [Accepted: 10/07/2009] [Indexed: 11/29/2022]
Abstract
BACKGROUND The transient outward current I(to) is of critical importance in regulating myocardial electrical properties during the very early phase of the action potential. The auxiliary beta subunit KCNE2 recently was shown to modulate I(to). OBJECTIVE The purpose of this study was to examine the contributions of KCNE2 and its two published variants (M54T, I57T) to I(to). METHODS The functional interaction between Kv4.3 (alpha subunit of human I(to)) and wild-type (WT), M54T, and I57T KCNE2, expressed in a heterologous cell line, was studied using patch-clamp techniques. RESULTS Compared to expression of Kv4.3 alone, co-expression of WT KCNE2 significantly reduced peak current density, slowed the rate of inactivation, and caused a positive shift of voltage dependence of steady-state inactivation curve. These modifications rendered Kv4.3 channels more similar to native cardiac I(to). Both M54T and I57T variants significantly increased I(to) current density and slowed the inactivation rate compared with WT KCNE2. Moreover, both variants accelerated the recovery from inactivation. CONCLUSION The study results suggest that KCNE2 plays a critical role in the normal function of the native I(to) channel complex in human heart and that M54T and I57T variants lead to a gain of function of I(to), which may contribute to generating potential arrhythmogeneity and pathogenesis for inherited fatal rhythm disorders.
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Affiliation(s)
- Jie Wu
- Pharmacology Department, Medical School of Xi'an Jiaotong University. Xi'an, Shaanxi, China
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62
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Lin YC, Huang J, Kan H, Frisbee JC, Yu HG. Rescue of a trafficking defective human pacemaker channel via a novel mechanism: roles of Src, Fyn, and Yes tyrosine kinases. J Biol Chem 2009; 284:30433-40. [PMID: 19748888 DOI: 10.1074/jbc.m109.039180] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Therapeutic strategies such as using channel blockers and reducing culture temperature have been used to rescue some long QT-associated voltage-gated potassium Kv trafficking defective mutant channels. A hyperpolarization-activated cyclic nucleotide-gated HCN4 pacemaker channel mutant (D553N) has been recently found in a patient associated with cardiac arrhythmias including long QT. D553N showed the defective trafficking to the cell surface, leading to little ionic current expression (loss-of-function). We show in this report that enhanced tyrosine phosphorylation mediated by Src, Fyn, and Yes kinases was able to restore the surface expression of D553N for normal current expression. Src or Yes, but not Fyn, significantly increased the current density and surface expression of D553N. Fyn accelerated the activation kinetics of the rescued D553N. Co-expression of D553N with Yes exhibited the slowest activation kinetics of D553N. Src, Fyn, and Yes significantly enhanced the tyrosine phosphorylation of D553N. A combination of Src, Fyn, and Yes rescued the current expression and the gating of D553N comparable with those of wild-type HCN4. In conclusion, we demonstrate a novel mechanism using three endogenous Src kinases to rescue a trafficking defective HCN4 mutant channel (D553N) by enhancing the tyrosine phosphorylation of the mutant channel protein.
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Affiliation(s)
- Yen-Chang Lin
- Department of Physiology and Pharmacology, West Virginia University School of Medicine, Center for Cardiovascular and Respiratory Sciences, Morgantown, West Virginia 26506, USA
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63
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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.
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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:
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64
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Baruscotti M, Barbuti A, Bucchi A. The cardiac pacemaker current. J Mol Cell Cardiol 2009; 48:55-64. [PMID: 19591835 DOI: 10.1016/j.yjmcc.2009.06.019] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/29/2009] [Revised: 06/15/2009] [Accepted: 06/26/2009] [Indexed: 12/17/2022]
Abstract
In mammals cardiac rate is determined by the duration of the diastolic depolarization of sinoatrial node (SAN) cells which is mainly determined by the pacemaker I(f) current. f-channels are encoded by four members of the hyperpolarization-activated cyclic nucleotide-gated gene (HCN1-4) family. HCN4 is the most abundant isoform in the SAN, and its relevance to pacemaking has been further supported by the discovery of four loss-of-function mutations in patients with mild or severe forms of cardiac rate disturbances. Due to its selective contribution to pacemaking, the I(f) current is also the pharmacological target of a selective heart rate-reducing agent (ivabradine) currently used in the clinical practice. Albeit to a minor extent, the I(f) current is also present in other spontaneously active myocytes of the cardiac conduction system (atrioventricular node and Purkinje fibres). In working atrial and ventricular myocytes f-channels are expressed at a very low level and do not play any physiological role; however in certain pathological conditions over-expression of HCN proteins may represent an arrhythmogenic mechanism. In this review some of the most recent findings on f/HCN channels contribution to pacemaking are described.
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Affiliation(s)
- Mirko Baruscotti
- Department of Biomolecular Sciences and Biotechnology, Laboratory of Molecular Physiology and Neurobiology, Università degli Studi di Milano, Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata (CIMMBA), via Celoria 26, 20133 Milano, Italy.
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65
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Atkinson SE, Williams SR. Postnatal development of dendritic synaptic integration in rat neocortical pyramidal neurons. J Neurophysiol 2009; 102:735-51. [PMID: 19458150 DOI: 10.1152/jn.00083.2009] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The dendritic tree of layer 5 (L5) pyramidal neurons spans the neocortical layers, allowing the integration of intra- and extracortical synaptic inputs. Here we investigate the postnatal development of the integrative properties of rat L5 pyramidal neurons using simultaneous whole cell recording from the soma and distal apical dendrite. In young (P9-10) neurons, apical dendritic excitatory synaptic input powerfully drove action potential output by efficiently summating at the axonal site of action potential generation. In contrast, in mature (P25-29) neurons, apical dendritic excitatory input provided little direct depolarization at the site of action potential generation but was integrated locally in the apical dendritic tree leading to the generation of dendritic spikes. Consequently, over the first postnatal month the fraction of action potentials driven by apical dendritic spikes increased dramatically. This developmental remodeling of the integrative operations of L5 pyramidal neurons was controlled by a >10-fold increase in the density of apical dendritic Hyperpolarization-activated cyclic nucleotide (HCN)-gated channels found in cell-attached patches or by immunostaining for the HCN channel isoform HCN1. Thus an age-dependent increase in apical dendritic HCN channel density ensures that L5 pyramidal neurons develop from compact temporal integrators to compartmentalized integrators of basal and apical dendritic synaptic input.
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Affiliation(s)
- Susan E Atkinson
- Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
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66
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Schweizer PA, Yampolsky P, Malik R, Thomas D, Zehelein J, Katus HA, Koenen M. Transcription profiling of HCN-channel isotypes throughout mouse cardiac development. Basic Res Cardiol 2009; 104:621-9. [PMID: 19421833 PMCID: PMC2758203 DOI: 10.1007/s00395-009-0031-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2008] [Accepted: 04/22/2009] [Indexed: 12/19/2022]
Abstract
Hyperpolarization-activated ion channels, encoded by four mammalian genes (HCN1-4), contribute in an important way to the cardiac pacemaker current If. Here, we describe the transcription profiles of the four HCN genes, the NRSF, KCNE2 and Kir2.1 genes from embryonic stage E9.5 dpc to postnatal day 120 in the mouse. Embryonic atrium and ventricle revealed abundant HCN4 transcription but other HCN transcripts were almost absent. Towards birth, HCN4 was downregulated in the atrium and almost vanished from the ventricle. After birth, however, HCN isotype transcription changed remarkably, showing increased levels of HCN1, HCN2 and HCN4 in the atrium and of HCN2 and HCN4 in the ventricle. HCN3 showed highest transcription at early embryonic stages and was hardly detectable thereafter. At postnatal day 10, HCN4 was highest in the sinoatrial node, being twofold higher than HCN1 and fivefold higher than HCN2. In the atrium, HCN4 was similar to HCN1 and sevenfold higher than HCN2. In the ventricle, in contrast, HCN2 was sixfold higher than HCN4, while HCN1 was absent. Subsequently all HCN isotype transcripts declined to lower adult levels, while ratios of HCN isotypes remained stable. In conclusion, substantial changes of HCN isotype transcription throughout cardiac development suggest that a regulated pattern of HCN isotypes is required to establish and ensure a stable heart rhythm. Furthermore, constantly low HCN transcription in adult myocardium may be required to prevent atrial and ventricular arrhythmogenesis.
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Affiliation(s)
- Patrick A Schweizer
- Universitätsklinikum Heidelberg, Innere Medizin III, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
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67
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Zhang Q, Huang A, Lin YC, Yu HG. Associated changes in HCN2 and HCN4 transcripts and I(f) pacemaker current in myocytes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:1138-47. [PMID: 19236845 DOI: 10.1016/j.bbamem.2009.02.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2008] [Revised: 02/07/2009] [Accepted: 02/11/2009] [Indexed: 11/18/2022]
Abstract
The time- and voltage-dependent inward current generated by the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels contributes to the tissue-specific rhythmic activities in the brain and heart. Four isoforms (HCN1-HCN4) have been identified. Previous studies showed that different HCN isoforms may form functional heteromeric channels. We report here that when HCN2 and HCN4 mRNA were injected into Xenopus oocytes with various ratios of HCN2 over HCN4 at 1:1, 10:1, and 1:10, respectively, the resultant channels showed a depolarized current activation and significantly faster activation kinetics near the midpoint of activation compared with HCN4 homomeric channels. In adult rat myocytes overexpressing HCN4, there was an associated increase in HCN2 mRNA. In neonatal rat myocytes in which HCN2 was knocked down, there was also a simultaneous decrease in HCN4 mRNA. Coimmunoprecipitation experiments showed that HCN2 and HCN4 channel proteins can associate with each other in adult rat ventricles. Finally, in adult myocytes overexpressing HCN4, the hyperpolarization-activated inward current activation, I(f), was shifted to physiological voltages from non-physiological voltages, associated with faster activation kinetics. These data suggested that different ratios of HCN2 and HCN4 transcripts overlapping in different tissues also contribute to the tissue-specific properties of I(f).
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Affiliation(s)
- Qi Zhang
- Center for Cardiovascular and Respiratory Sciences, Department of Physiology, West Virginia University School of Medicine, Morgantown, West Virginia 26506, USA
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Pacemaker activity of the human sinoatrial node: role of the hyperpolarization-activated current, I(f). Int J Cardiol 2009; 132:318-36. [PMID: 19181406 DOI: 10.1016/j.ijcard.2008.12.196] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2008] [Revised: 12/16/2008] [Accepted: 12/22/2008] [Indexed: 11/20/2022]
Abstract
The mechanism of primary, spontaneous cardiac pacemaker activity of the sinoatrial node (SAN) has extensively been studied in several animal species, but is virtually unexplored in man. Understanding the mechanisms of human SAN pacemaker activity is important for developing new therapeutic approaches for controlling the heart rate in the sick sinus syndrome and in diseased myocardium. Here we review the functional role of the hyperpolarization-activated 'funny' current, I(f), in human SAN pacemaker activity. Despite the many animal studies performed over the years, the contribution of I(f) to pacemaker activity is still controversial and not fully established. However, recent clinical data on mutations in the I(f) encoding HCN4 gene, which is thought to be the most abundant isoform of the HCN gene family in SAN, suggest a functional role of I(f) in human pacemaker activity. These clinical findings are supported by recent experimental data from single isolated human SAN cells that provide direct evidence that I(f) contributes to human SAN pacemaker activity. Therefore, controlling heart rate in clinical practice via I(f) blockers offers a valuable approach to lowering heart rate and provides an attractive alternative to conventional treatment for a wide range of patients with confirmed stable angina, while upregulation or artificial expression of I(f) may relieve disease-causing bradycardias.
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69
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Roepke TK, Kontogeorgis A, Ovanez C, Xu X, Young JB, Purtell K, Goldstein PA, Christini DJ, Peters NS, Akar FG, Gutstein DE, Lerner DJ, Abbott GW. Targeted deletion of kcne2 impairs ventricular repolarization via disruption of I(K,slow1) and I(to,f). FASEB J 2008; 22:3648-60. [PMID: 18603586 DOI: 10.1096/fj.08-110171] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Mutations in human KCNE2, which encodes the MiRP1 potassium channel ancillary subunit, associate with long QT syndrome (LQTS), a defect in ventricular repolarization. The precise cardiac role of MiRP1 remains controversial, in part, because it has marked functional promiscuity in vitro. Here, we disrupted the murine kcne2 gene to define the role of MiRP1 in murine ventricles. kcne2 disruption prolonged ventricular action potential duration (APD), suggestive of reduced repolarization capacity. Accordingly, kcne2 (-/-) ventricles exhibited a 50% reduction in I(K,slow1), generated by Kv1.5--a previously unknown partner for MiRP1. I(to,f), generated by Kv4 alpha subunits, was also diminished, by approximately 25%. Ventricular MiRP1 protein coimmunoprecipitated with native Kv1.5 and Kv4.2 but not Kv1.4 or Kv4.3. Unexpectedly, kcne2 (-/-) ventricular membrane fractions exhibited 50% less mature Kv1.5 protein than wild type, and disruption of Kv1.5 trafficking to the intercalated discs. Consistent with the reduction in ventricular K(+) currents and prolonged ventricular APD, kcne2 deletion lengthened the QT(c) under sevoflurane anesthesia. Thus, targeted disruption of kcne2 has revealed a novel cardiac partner for MiRP1, a novel role for MiRPs in alpha subunit targeting in vivo, and a role for MiRP1 in murine ventricular repolarization with parallels to that proposed for the human heart.
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Affiliation(s)
- Torsten K Roepke
- Greenberg Division of Cardiology, Department of Medicine, Weill Medical College of Cornell University, 1300 York Ave., New York, NY 10065, USA
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70
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Stillitano F, Lonardo G, Zicha S, Varro A, Cerbai E, Mugelli A, Nattel S. Molecular basis of funny current (If) in normal and failing human heart. J Mol Cell Cardiol 2008; 45:289-99. [PMID: 18556018 DOI: 10.1016/j.yjmcc.2008.04.013] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2008] [Revised: 04/28/2008] [Accepted: 04/30/2008] [Indexed: 11/17/2022]
Abstract
I(f) overexpression has been functionally demonstrated in ventricular myocytes from failing human hearts. Altered expression of I(f)-channels as a consequence of electrophysiological remodeling may represent an arrhythmogenic mechanism in heart failure; however, the molecular basis of I(f) overexpression in human cardiac disease is unknown. HCN1, 2 and 4 subtypes, which encode I(f)-channels, have been identified in the heart. The present study was designed to characterize HCN isoform expression in failing and non-failing hearts. Ventricular and atrial samples were obtained from normal or failing hearts explanted from patients with end-stage ischemic cardiomyopathy. I(f) was recorded in patch-clamped left ventricular myocytes. mRNA and protein expression of HCN subunits were measured in both atria and ventricles of control and diseased hearts. HCN2 and HCN4 were detected in human myocardium. Both mRNA and protein levels of HCN2/4 were significantly augmented in failing ventricles (p<0.01 for mRNA, p<0.05 for protein). These results are consistent with the electrophysiological data showing that, in failing ventricular myocytes, I(f) is of larger amplitude and activates at less negative potential. Changes in mRNA and protein expression of both HCN2/4 isoforms in atrial specimens from patients with heart failure mirrored those observed in ventricles (p<0.001 for mRNA, p<0.05 for protein). No disease-dependent alteration was detected for MiRP1, the putative beta-subunit of the I(f)-channel. In conclusion, HCN4 is the predominant channel subtype in normal human heart, and its expression is further amplified by disease. HCN upregulation likely contributes to increased I(f) and may play a role in ventricular and atrial arrhythmogenesis in heart failure.
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Affiliation(s)
- Francesca Stillitano
- Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata (CIMMBA), University of Florence, Viale Pieraccini 6, 50139 Florence, Italy
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71
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Jiang YQ, Sun Q, Tu HY, Wan Y. Characteristics of HCN channels and their participation in neuropathic pain. Neurochem Res 2008; 33:1979-89. [PMID: 18461446 DOI: 10.1007/s11064-008-9717-6] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2008] [Accepted: 04/11/2008] [Indexed: 02/08/2023]
Abstract
Neuropathic pain is induced by the injury to nervous systems and characterized by hyperalgesia, allodynia and spontaneous pain. The underlying mechanisms include peripheral and central sensitization resulted from neuronal hyperexcitability. A number of ion channels are considered to contribute to the neuronal hyperexcitability. Here, we particularly concentrate on an interesting ion channel, hyperpolarization-activated cyclic nucleotide gated (HCN) channels. We overview its biophysical properties, physiological functions, followed by focusing on the current progress in the study of its role in the development of neuropathic pain. We attempt to provide a comprehensive review of the potential valuable target, HCN channels, in the treatment of neuropathic pain.
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Affiliation(s)
- Yu-Qiu Jiang
- Neuroscience Research Institute, Peking University, 38 Xueyuan Road, Beijing 100083, People's Republic of China
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72
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Xu SZ, Zhong W, Watson NM, Dickerson E, Wake JD, Lindow SW, Newton CJ, Atkin SL. Fluvastatin reduces oxidative damage in human vascular endothelial cells by upregulating Bcl-2. J Thromb Haemost 2008; 6:692-700. [PMID: 18221360 DOI: 10.1111/j.1538-7836.2008.02913.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND 3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have been widely used in clinical practise and their efficacy in reducing cardiovascular risk has been well described. OBJECTIVES To investigate the effect of low doses of fluvastatin (nanomolar) on H(2)O(2)-induced cell damage and the underlying mechanism. METHODS AND RESULTS Primary cultures of human umbilical vein endothelial cells were used, and the effects of fluvastatin on H(2)O(2)-induced apoptosis, necrosis, and proliferation were observed. H(2)O(2) at a concentration of 100 mum significantly induced apoptotic cell death after 24-h cell culture. Fluvastatin at low concentrations (10-100 nm) prevented H(2)O(2)-induced apoptosis, as determined by a DNA fragmentation assay and by cell counting with trypan blue and Hoechst 33342 nuclei staining. The protective effect of fluvastatin was mediated by the upregulation of Bcl-2 expression as probed by real-time polymerase chain reaction and Western blotting. Using siRNA to knock down the expression of Bcl-2, the protective effect of fluvastatin was abolished. Fluvastatin had no direct effect on the H(2)O(2)-sensitive TRPM2 calcium channel. CONCLUSIONS These results suggest that fluvastatin has a potent protective effect against H(2)O(2)-induced apoptosis via upregulation of Bcl-2 expression. The findings provide a new insight into the mechanism by which fluvastatin is able to modulate the influence of oxidative stress on vascular endothelial cells.
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Affiliation(s)
- S Z Xu
- Postgraduate Medical Institute and Hull York Medical School, University of Hull, Hull, UK.
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73
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Hyperpolarization-activated cyclic nucleotide-gated channel mRNA and protein expression in large versus small diameter dorsal root ganglion neurons: correlation with hyperpolarization-activated current gating. Neuroscience 2008; 153:1008-19. [PMID: 18450385 DOI: 10.1016/j.neuroscience.2008.03.032] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2007] [Revised: 03/06/2008] [Accepted: 03/07/2008] [Indexed: 12/19/2022]
Abstract
Hyperpolarization-activated cyclic nucleotide-gated channels (HCN) are responsible for the functional hyperpolarization-activated current (I(h)) in dorsal root ganglion (DRG) neurons. We studied HCN1-4 channel mRNA and protein expression and correlated these findings with I(h) functional properties in rat DRG neurons of different size. Quantitative RT-PCR (TaqMan) analysis demonstrated that HCN2 and HCN1 mRNAs were more abundantly expressed in large diameter (55-80 microm) neurons, while HCN3 mRNA was preferentially expressed in small diameter (20-30 microm) neurons. HCN4 mRNA expression was very low in neurons of all sizes. At the protein level, subunit-selective polyclonal antibodies and immunofluorescence indicated that HCN1 and HCN3 are present in large diameter neurons and small diameter neurons. Staining in small diameter neurons was in IB4-positive (non-peptidergic) and IB4-negative (peptidergic) cells. HCN2 immunofluorescent staining was heterogeneous and predominantly in large diameter neurons and in small diameter IB4-negative neurons. HCN4 was poorly expressed in all neurons. Functionally, I(h) amplitude and density were significantly larger, and activation kinetics faster, in large diameter neurons when compared with small neurons. I(h) activation rates in small and large diameter DRG neurons were consistent with the relative abundance of HCN subunits in the respective cell type, considering the reported HCN channel activation rates in heterologous systems (HCN1>HCN2 approximately HCN3>HCN4), suggesting exclusivity of roles of different HCN subunits contributing to the excitability of DRG neurons of different size. Additionally, a functional role of I(h) in small DRG neuron excitability was evaluated using a computational model.
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74
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Michels G, Er F, Khan IF, Endres-Becker J, Brandt MC, Gassanov N, Johns DC, Hoppe UC. K+ channel regulator KCR1 suppresses heart rhythm by modulating the pacemaker current If. PLoS One 2008; 3:e1511. [PMID: 18231597 PMCID: PMC2204056 DOI: 10.1371/journal.pone.0001511] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2007] [Accepted: 12/22/2007] [Indexed: 01/20/2023] Open
Abstract
Hyperpolarization-activated, cyclic nucleotide sensitive (HCN) channels underlie the pacemaker current I(f), which plays an essential role in spontaneous cardiac activity. HCN channel subunits (HCN1-4) are believed to be modulated by additional regulatory proteins, which still have to be identified. Using biochemistry, molecularbiology and electrophysiology methods we demonstrate a protein-protein interaction between HCN2 and the K(+) channel regulator protein 1, named KCR1. In coimmunoprecipitation experiments we show that KCR1 and HCN2 proteins are able to associate. Heterologously expressed HCN2 whole-cell current density was significantly decreased by KCR1. KCR1 profoundly suppressed I(HCN2) single-channel activity, indicating a functional interaction between KCR1 and the HCN2 channel subunit. Endogenous KCR1 expression could be detected in adult and neonatal rat ventriculocytes. Adenoviral-mediated overexpression of KCR1 in rat cardiomyocytes (i) reduced I(f) whole-cell currents, (ii) suppressed most single-channel gating parameters, (iii) altered the activation kinetics, (iv) suppressed spontaneous action potential activity, and (v) the beating rate. More importantly, siRNA-based knock-down of endogenous KCR1 increased the native I(f) current size and single-channel activity and accelerated spontaneous beating rate, supporting an inhibitory action of endogenous KCR1 on native I(f). Our observations demonstrate for the first time that KCR1 modulates I(HCN2)/I(f) channel gating and indicate that KCR1 serves as a regulator of cardiac automaticity.
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Affiliation(s)
- Guido Michels
- Department of Internal Medicine III, University of Cologne, Cologne, Germany
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75
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Li CH, Zhang Q, Teng B, Mustafa SJ, Huang JY, Yu HG. Src tyrosine kinase alters gating of hyperpolarization-activated HCN4 pacemaker channel through Tyr531. Am J Physiol Cell Physiol 2008; 294:C355-62. [PMID: 17977941 PMCID: PMC2784909 DOI: 10.1152/ajpcell.00236.2007] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We recently discovered that the constitutively active Src tyrosine kinase can enhance hyperpolarization-activated, cyclic nucleotide-gated (HCN) 4 channel activity by binding to the channel protein. To investigate the mechanism of modulation by Src of HCN channels, we studied the effects of a selective inhibitor of Src tyrosine kinase, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), on HCN4 and its mutant channels expressed in HEK 293 cells by using a whole cell patch-clamp technique. We found that PP2 can inhibit HCN4 currents by negatively shifting the voltage dependence of channel activation, decreasing the whole cell channel conductance, and slowing activation and deactivation kinetics. Screening putative tyrosine residues subject to phosphorylation yielded two candidates: Tyr(531) and Tyr(554). Substituting HCN4-Tyr(531) with phenylalanine largely abolished the effects of PP2 on HCN4 channels. Replacing HCN4-Tyr(554) with phenylalanine did not abolish the effects of PP2 on voltage-dependent activation but did eliminate PP2-induced slowing of channel kinetics. The inhibitory effects of HCN channels associated with reduced Src tyrosine activity is confirmed in HL-1 cardiomyocytes. Finally, we found that PP2 can decrease the heart rate in a mouse model. These results demonstrate that Src tyrosine kinase enhances HCN4 currents by shifting their activation to more positive potentials and increasing the whole cell channel conductance as well as speeding the channel kinetics. The tyrosine residue that mediates most of Src's actions on HCN4 channels is Tyr(531).
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Affiliation(s)
- Chen-Hong Li
- Department of Physiology and Pharmacology, Center for Interdisciplinary Research in Cardiovascular Sciences, West Virginia University School of Medicine, Morgantown, WV 26506, USA
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76
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Cangiano L, Gargini C, Della Santina L, Demontis GC, Cervetto L. High-pass filtering of input signals by the Ih current in a non-spiking neuron, the retinal rod bipolar cell. PLoS One 2007; 2:e1327. [PMID: 18091997 PMCID: PMC2129120 DOI: 10.1371/journal.pone.0001327] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2007] [Accepted: 11/26/2007] [Indexed: 11/18/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-sensitive (HCN) channels mediate the I(f) current in heart and I(h) throughout the nervous system. In spiking neurons I(h) participates primarily in different forms of rhythmic activity. Little is known, however, about its role in neurons operating with graded potentials as in the retina, where all four channel isoforms are expressed. Intriguing evidence for an involvement of I(h) in early visual processing are the side effects reported, in dim light or darkness, by cardiac patients treated with HCN inhibitors. Moreover, electroretinographic recordings indicate that these drugs affect temporal processing in the outer retina. Here we analyzed the functional role of HCN channels in rod bipolar cells (RBCs) of the mouse. Perforated-patch recordings in the dark-adapted slice found that RBCs exhibit I(h), and that this is sensitive to the specific blocker ZD7288. RBC input impedance, explored by sinusoidal frequency-modulated current stimuli (0.1-30 Hz), displays band-pass behavior in the range of I(h) activation. Theoretical modeling and pharmacological blockade demonstrate that high-pass filtering of input signals by I(h), in combination with low-pass filtering by passive properties, fully accounts for this frequency-tuning. Correcting for the depolarization introduced by shunting through the pipette-membrane seal, leads to predict that in darkness I(h) is tonically active in RBCs and quickens their responses to dim light stimuli. Immunohistochemistry targeting candidate subunit isoforms HCN1-2, in combination with markers of RBCs (PKC) and rod-RBC synaptic contacts (bassoon, mGluR6, Kv1.3), suggests that RBCs express HCN2 on the tip of their dendrites. The functional properties conferred by I(h) onto RBCs may contribute to shape the retina's light response and explain the visual side effects of HCN inhibitors.
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Affiliation(s)
- Lorenzo Cangiano
- Dipartimento di Psichiatria e Neurobiologia, Università di Pisa, Pisa, Italy.
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77
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Komagiri Y, Kitamura N. Comparison of effects of PKA catalytic subunit on I(h) and calcium channel currents in rat dorsal root ganglion cells. ACTA ACUST UNITED AC 2007; 28:177-89. [PMID: 17878598 DOI: 10.2220/biomedres.28.177] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
We investigated whether PKA-induced phosphorylation was involved in regulation of hyperpolarization-activated current (I(h)) in rat dorsal root ganglion (DRG) cells. We examined the effect of the catalytic subunit of PKA (PKAc) on I(h) and confirmed an effect of PKAc on Ca(2+) channel currents carried by Ba(2+) (I(Ba)) in identical neurons as a positive control of PKA activity. After the start of recording, amplitudes of I(Ba) gradually decreased (rundown). An intracellular application of ATP reduced the rundown of I(Ba) and induced a depolarizing shift of I(h) activation. The former was partially reversed by PKI but the latter was not affected. An intracellular application of PKAc also prevented the rundown of I(Ba) and this effect was potentiated by okadaic acid (OA). The application of PKAc and OA in combination did not change the electrophysiological properties of I(h) although a potentiating effect on I(Ba) was observed in the same neurons. The application of 2-mM ATP in addition to PKAc and OA did not result in an additional potentiation of I(Ba), but shifted the activation curve of I(h) positively. These results suggested that PKA-induced phosphorylation was not involved in the modulatory mechanisms of I(h) in rat DRG neurons.
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Affiliation(s)
- You Komagiri
- Laboratory of Physiology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan
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78
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Um SY, McDonald TV. Differential association between HERG and KCNE1 or KCNE2. PLoS One 2007; 2:e933. [PMID: 17895974 PMCID: PMC1978535 DOI: 10.1371/journal.pone.0000933] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2007] [Accepted: 09/04/2007] [Indexed: 12/16/2022] Open
Abstract
The small proteins encoded by KCNE1 and KCNE2 have both been proposed as accessory subunits for the HERG channel. Here we report our investigation into the cell biology of the KCNE-HERG interaction. In a co-expression system, KCNE1 was more readily co-precipitated with co-expressed HERG than was KCNE2. When forward protein trafficking was prevented (either by Brefeldin A or engineering an ER-retention/retrieval signal onto KCNE cDNA) the intracellular abundance of KCNE2 and its association with HERG markedly increased relative to KCNE1. HERG co-localized more completely with KCNE1 than with KCNE2 in all the membrane-processing compartments of the cell (ER, Golgi and plasma membrane). By surface labeling and confocal immunofluorescence, KCNE2 appeared more abundant at the cell surface compared to KCNE1, which exhibited greater co-localization with the ER-marker calnexin. Examination of the extracellular culture media showed that a significant amount of KCNE2 was extracellular (both soluble and membrane-vesicle-associated). Taken together, these results suggest that during biogenesis of channels HERG is more likely to assemble with KCNE1 than KCNE2 due to distinctly different trafficking rates and retention in the cell rather than differences in relative affinity. The final channel subunit constitution, in vivo, is likely to be determined by a combination of relative cell-to-cell expression rates and differential protein processing and trafficking.
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Affiliation(s)
- Sung Yon Um
- Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, USA
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79
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Angelo K, London M, Christensen SR, Häusser M. Local and global effects of I(h) distribution in dendrites of mammalian neurons. J Neurosci 2007; 27:8643-53. [PMID: 17687042 PMCID: PMC6672943 DOI: 10.1523/jneurosci.5284-06.2007] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The hyperpolarization-activated cation current I(h) exhibits a steep gradient of channel density in dendrites of pyramidal neurons, which is associated with location independence of temporal summation of EPSPs at the soma. In striking contrast, here we show by using dendritic patch-clamp recordings that in cerebellar Purkinje cells, the principal neurons of the cerebellar cortex, I(h) exhibits a uniform dendritic density, while location independence of EPSP summation is observed. Using compartmental modeling in realistic and simplified dendritic geometries, we demonstrate that the dendritic distribution of I(h) only weakly affects the degree of temporal summation at the soma, while having an impact at the dendritic input location. We further analyze the effect of I(h) on temporal summation using cable theory and derive bounds for temporal summation for any spatial distribution of I(h). We show that the total number of I(h) channels, not their distribution, governs the degree of temporal summation of EPSPs. Our findings explain the effect of I(h) on EPSP shape and temporal summation, and suggest that neurons are provided with two independent degrees of freedom for different functions: the total amount of I(h) (controlling the degree of temporal summation of dendritic inputs at the soma) and the dendritic spatial distribution of I(h) (regulating local dendritic processing).
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Affiliation(s)
- Kamilla Angelo
- Wolfson Institute for Biomedical Research and Department of Physiology, University College London, London WC1E 6BT, United Kingdom
| | - Michael London
- Wolfson Institute for Biomedical Research and Department of Physiology, University College London, London WC1E 6BT, United Kingdom
| | - Soren R. Christensen
- Wolfson Institute for Biomedical Research and Department of Physiology, University College London, London WC1E 6BT, United Kingdom
| | - Michael Häusser
- Wolfson Institute for Biomedical Research and Department of Physiology, University College London, London WC1E 6BT, United Kingdom
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80
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Abstract
Hyperpolarization-activated cation nonselective cyclic nucleotide-gated (HCN) channels mediate pacemaker currents that control basic rhythmic processes including heartbeat. Alterations in HCN channel expression or function have been described in both epilepsy and cardiac arrhythmias. Recent evidence suggests that pacemaker currents may also play an important role in ectopic neuronal activity that manifests as neuropathic pain. Pacemaker currents are subject to endogenous regulation by cyclic nucleotides, pH and perhaps phosphorylation. In addition, a number of neuromodulators with known roles in pain affect current density and kinetics. The pharmacology of a number of drugs that are commonly used to treat neuropathic pain includes effects on pacemaker currents. Altered pacemaker currents in injured tissues may be an important mechanism underlying neuropathic pain, and drugs that modulate these currents may offer new therapeutic options.
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Affiliation(s)
- Sean M Brown
- Johnson & Johnson Pharmaceutical Research & Development, L.L.C., San Diego, California, USA. schaplan@
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81
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Abstract
kcne are evolutionarily conserved genes that encode accessory subunits of voltage-gated K(+) (Kv) channels. Missense mutations in kcne1, kcne2, and kcne3 are linked to congenital and acquired channelopathies in Homo sapiens. Here we show an unique example of conservation of kcne activities at genetic, physiological, functional, and pathophysiological level in Caenorhabditis elegans. Thus, mps-4 is the homologue of kcne1 that operates in human heart and inner ear. Like its KCNE relatives, MPS-4 assembles with a Kv channel, EXP-2, to form a complex that controls pharyngeal muscle contractility. MPS-4 modulates EXP-2 function in a similar fashion as KCNE proteins endow human channels. When defective, MPS-4, can induce abnormal repolarization by mechanisms that resemble the way KCNE proteins are thought to provoke arrhythmia in human heart. Mutation of a conserved aspartate residue associated with human disease (MPS-4-D74N) alters the functional attributes of the C. elegans current. Taken together these data underscore a significant conservation of KCNE activities in different pumps. This implies that C. elegans can develop into a system to study the molecular and genetic basis of KCNE-mediated muscle contractility and disease states.
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Affiliation(s)
- Ki Ho Park
- University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Department of Physiology and Biophysics, Piscataway, New Jersey 08854, USA
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82
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Schridde U, Strauss U, Bräuer AU, van Luijtelaar G. Environmental manipulations early in development alter seizure activity, Ih and HCN1 protein expression later in life. Eur J Neurosci 2007; 23:3346-58. [PMID: 16820024 DOI: 10.1111/j.1460-9568.2006.04865.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Although absence epilepsy has a genetic origin, evidence from an animal model (Wistar Albino Glaxo/Rijswijk; WAG/Rij) suggests that seizures are sensitive to environmental manipulations. Here, we show that manipulations of the early rearing environment (neonatal handling, maternal deprivation) of WAG/Rij rats leads to a pronounced decrease in seizure activity later in life. Recent observations link seizure activity in WAG/Rij rats to the hyperpolarization-activated cation current (Ih) in the somatosensory cortex, the site of seizure generation. Therefore, we investigated whether the alterations in seizure activity between rats reared differently might be correlated with changes in Ih and its channel subunits hyperpolarization-activated cation channel HCN1, 2 and 4. Whole-cell recordings from layer 5 pyramidal neurons, in situ hybridization and Western blot of the somatosensory cortex revealed an increase in Ih and HCN1 in neonatal handled and maternal deprived, compared to control rats. The increase was specific to HCN1 protein expression and did not involve HCN2/4 protein expression, or mRNA expression of any of the subunits (HCN1, 2, 4). Our findings provide the first evidence that relatively mild changes in the neonatal environment have a long-term impact of absence seizures, Ih and HCN1, and suggest that an increase of Ih and HCN1 is associated with absence seizure reduction. Our findings shed new light on the role of Ih and HCN in brain functioning and development and demonstrate that genetically determined absence seizures are quite sensitive for early interventions.
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Affiliation(s)
- Ulrich Schridde
- Department of Neurology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8018, USA.
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83
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Panaghie G, Abbott GW. The role of S4 charges in voltage-dependent and voltage-independent KCNQ1 potassium channel complexes. ACTA ACUST UNITED AC 2007; 129:121-33. [PMID: 17227916 PMCID: PMC2154355 DOI: 10.1085/jgp.200609612] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Voltage-gated potassium (Kv) channels extend their functional repertoire by coassembling with MinK-related peptides (MiRPs). MinK slows the activation of channels formed with KCNQ1 α subunits to generate the voltage-dependent IKs channel in human heart; MiRP1 and MiRP2 remove the voltage dependence of KCNQ1 to generate potassium “leak” currents in gastrointestinal epithelia. Other Kv α subunits interact with MiRP1 and MiRP2 but without loss of voltage dependence; the mechanism for this disparity is unknown. Here, sequence alignments revealed that the voltage-sensing S4 domain of KCNQ1 bears lower net charge (+3) than that of any other eukaryotic voltage-gated ion channel. We therefore examined the role of KCNQ1 S4 charges in channel activation using alanine-scanning mutagenesis and two-electrode voltage clamp. Alanine replacement of R231, at the N-terminal side of S4, produced constitutive activation in homomeric KCNQ1 channels, a phenomenon not observed with previous single amino acid substitutions in S4 of other channels. Homomeric KCNQ4 channels were also made constitutively active by mutagenesis to mimic the S4 charge balance of R231A-KCNQ1. Loss of single S4 charges at positions R231 or R237 produced constitutively active MinK-KCNQ1 channels and increased the constitutively active component of MiRP2-KCNQ1 currents. Charge addition to the CO2H-terminal half of S4 eliminated constitutive activation in MiRP2-KCNQ1 channels, whereas removal of homologous charges from KCNQ4 S4 produced constitutively active MiRP2-KCNQ4 channels. The results demonstrate that the unique S4 charge paucity of KCNQ1 facilitates its unique conversion to a leak channel by ancillary subunits such as MiRP2.
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Affiliation(s)
- Gianina Panaghie
- Greenberg Division of Cardiology, Department of Medicine, Cornell University, Weill Medical College, New York, NY 10021, USA
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84
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Pian P, Bucchi A, Robinson RB, Siegelbaum SA. Regulation of gating and rundown of HCN hyperpolarization-activated channels by exogenous and endogenous PIP2. ACTA ACUST UNITED AC 2006; 128:593-604. [PMID: 17074978 PMCID: PMC2151583 DOI: 10.1085/jgp.200609648] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The voltage dependence of activation of the HCN hyperpolarization-activated cation channels is shifted in inside-out patches by −40 to −60 mV relative to activation in intact cells, a phenomenon referred to as rundown. Less than 20 mV of this hyperpolarizing shift can be due to the influence of the canonical modulator of HCN channels, cAMP. Here we study the role of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) in HCN channel rundown, as hydrolysis of PI(4,5)P2 by lipid phosphatases is thought to underlie rundown of several other channels. We find that bath application of exogenous PI(4,5)P2 reverses the effect of rundown, producing a large depolarizing shift in HCN2 activation. A synthetic short chain analogue of PI(4,5)P2, dioctanoyl phosphatidylinositol 4,5-bisphosphate, shifts the HCN2 activation curve to more positive potentials in a dose-dependent manner. Other dioctanoyl phosphatidylinositides with one or more phosphates on the lipid headgroup also shift activation, although phosphatidylinositol (PI) is ineffective. Several lines of evidence suggest that HCN2 is also regulated by endogenous PI(4,5)P2: (a) blockade of phosphatases slows the hyperpolarizing shift upon patch excision; (b) application of an antibody that binds and depletes membrane PIP2 causes a further hyperpolarizing shift in activation; (c) the shift in activation upon patch excision can be partially reversed by MgATP; and (d) the effect of MgATP is blocked by wortmannin, an inhibitor of PI kinases. Finally, recordings from rabbit sinoatrial cells demonstrate that diC8 PI(4,5)P2 delays the rundown of native HCN currents. Thus, both native and recombinant HCN channels are regulated by PI(4,5)P2.
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Affiliation(s)
- Phillip Pian
- Center for Neurobiology and Behavior, Columbia University Medical Center, New York, NY 10032, USA
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85
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Wu DM, Jiang M, Zhang M, Liu XS, Korolkova YV, Tseng GN. KCNE2 is colocalized with KCNQ1 and KCNE1 in cardiac myocytes and may function as a negative modulator of IKs current amplitude in the heart. Heart Rhythm 2006; 3:1469-80. [PMID: 17161791 DOI: 10.1016/j.hrthm.2006.08.019] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2006] [Accepted: 08/14/2006] [Indexed: 11/18/2022]
Abstract
BACKGROUND In heterologous expression systems, KCNE1 and KCNE2 each can associate with KCNQ1 and exert apparently opposite effects on its channel function. KCNQ1 and KCNE1 associate to form the slow delayed rectifier I(Ks) channels in the heart. Whether KCNE2 plays any role in I(Ks) function is not clear. OBJECTIVES The purpose of this study was to study whether KCNE2 can associate with KCNQ1 in the presence of KCNE1 and modulate its function. METHODS Voltage clamp methods were used to study channel function in cardiomyocytes and in oocytes or COS-7 cells and immunocytochemistry/coimmunoprecipitation was used to study protein colocalization/association. RESULTS Adult rat ventricular myocytes express functional I(Ks), and KCNE2 is colocalized with KCNQ1 and KCNE1 at surface membrane and t-tubules. A detailed study of KCNQ1 modulation by KCNE2 at different KCNE2 expression levels reveals that, surprisingly, KCNE2 and KCNE1 share the major features in modulating KCNQ1 gating kinetics: slowing of activation, positive shift in the voltage range of activation, and suppression of inactivation. However, KCNE2 reduces KCNQ1 current amplitude whereas KCNE1 increases it, and KCNE2 induces a constitutively active KCNQ1 component whereas KCNE1 does not. Coimmunoprecipitation suggests that KCNQ1, KCNE1, and KCNE2 can form a tripartite complex, indicating that KCNE2 can bind to KCNQ1 in the presence of KCNE1. Coexpressing KCNE2 with KCNQ1 and KCNE1 leads to a decrease in the I(Ks) current amplitude without altering the gating kinetics. CONCLUSION Our data suggest that KCNE2 is in close proximity to KCNQ1 and KCNE1 in cardiomyocytes and may participate in dynamic regulation of I(Ks) current amplitude in the heart.
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Affiliation(s)
- Dong-Mei Wu
- Department of Physiology, Virginia Commonwealth University, Richmond, Virginia 23298, USA
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86
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Surges R, Brewster AL, Bender RA, Beck H, Feuerstein TJ, Baram TZ. Regulated expression of HCN channels and cAMP levels shape the properties of the h current in developing rat hippocampus. Eur J Neurosci 2006; 24:94-104. [PMID: 16882011 PMCID: PMC2919221 DOI: 10.1111/j.1460-9568.2006.04880.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The hyperpolarization-activated current (I(h)) contributes to intrinsic properties and network responses of neurons. Its biophysical properties depend on the expression profiles of the underlying hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels and the presence of cyclic AMP (cAMP) that potently and differentially modulates I(h) conducted by HCN1, HCN2 and/or HCN4. Here, we studied the properties of I(h) in hippocampal CA1 pyramidal cells, the developmental evolution of the HCN-subunit isoforms that contribute to this current, and their interplay with age-dependent free cAMP concentrations, using electrophysiological, molecular and biochemical methods. I(h) amplitude increased progressively during the first four postnatal weeks, consistent with the observed overall increased expression of HCN channels. Activation kinetics of the current accelerated during this period, consonant with the quantitative reduction of mRNA and protein expression of the slow-kinetics HCN4 isoform and increased levels of HCN1. The sensitivity of I(h) to cAMP, and the contribution of the slow component to the overall I(h), decreased with age. These are likely a result of the developmentally regulated transition of the complement of HCN channel isoforms from cAMP sensitive to relatively cAMP insensitive. Thus, although hippocampal cAMP concentrations increased over twofold during the developmental period studied, the coordinated changes in expression of three HCN channel isoforms resulted in reduced effects of this signalling molecule on neuronal h currents.
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Affiliation(s)
- Rainer Surges
- Department of Neurology, University Clinics Freiburg, Breisacher Strasse 64, 79106 Freiburg, Germany.
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87
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Abstract
Voltage-gated potassium channels regulate cell membrane potential and excitability in neurons and other cell types. A precise control of neuronal action potential patterns underlies the basic functioning of the central and peripheral nervous system. This control relies on the adaptability of potassium channel activities. The functional diversity of potassium currents, however, far exceeds the considerable molecular diversity of this class of genes. Potassium current diversity contributes to the specificity of neuronal firing patterns and may be achieved by regulated transcription, RNA splicing, and posttranslational modifications. Another mechanism for regulation of potassium channel activity is through association with interacting proteins and accessory subunits. Here the authors highlight recent work that addresses this growing area of exploration and discuss areas of future investigation.
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Affiliation(s)
- Yan Li
- Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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88
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Toyoda F, Ueyama H, Ding WG, Matsuura H. Modulation of functional properties of KCNQ1 channel by association of KCNE1 and KCNE2. Biochem Biophys Res Commun 2006; 344:814-20. [PMID: 16631607 DOI: 10.1016/j.bbrc.2006.03.213] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2006] [Accepted: 03/28/2006] [Indexed: 11/27/2022]
Abstract
The KCNE proteins (KCNE1 through KCNE5) function as beta-subunits of several voltage-gated K(+) channels. Assembly of KCNQ1 K(+) channel alpha-subunits and KCNE1 underlies cardiac I(Ks), while KCNQ1 interacts with all other members of KCNE forming complexes with different properties. Here we investigated synergic actions of KCNE1 and KCNE2 on functional properties of KCNQ1 heterologously expressed in COS7 cells. Patch-clamp recordings from cells expressing KCNQ1 and KCNE1 exhibited the slowly activating current, while co-expression of KCNQ1 with KCNE2 produced a practically time-independent current. When KCNQ1 was co-expressed with both of KCNE1 and KCNE2, the membrane current exhibited a voltage- and time-dependent current whose characteristics differed substantially from those of the KCNQ1/KCNE1 current. The KCNQ1/KCNE1/KCNE2 current had a more depolarized activation voltage, a faster deactivation kinetics, and a less sensitivity to activation by mefenamic acid. These results suggest that KCNE2 can functionally couple to KCNQ1 even in the presence of KCNE1.
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Affiliation(s)
- Futoshi Toyoda
- Department of Physiology, Shiga University of Medical Science, Seta-Tsukinowa, Otsu, Shiga 520-2192, Japan.
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89
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Kuisle M, Wanaverbecq N, Brewster AL, Frère SGA, Pinault D, Baram TZ, Lüthi A. Functional stabilization of weakened thalamic pacemaker channel regulation in rat absence epilepsy. J Physiol 2006; 575:83-100. [PMID: 16728450 PMCID: PMC1819420 DOI: 10.1113/jphysiol.2006.110486] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Aberrant function of pacemaker currents (Ih), carried by hyperpolarization-activated cation non-selective (HCN) channels, affects neuronal excitability and accompanies epilepsy, but its distinct roles in epileptogenesis and chronic epilepsy are unclear. We probed Ih function and subunit composition during both pre- and chronically epileptic stages in thalamocortical (TC) neurones of the Genetic Absence Epilepsy Rat from Strasbourg (GAERS). Voltage gating of Ih was unaltered in mature somatosensory TC cells, both in vivo and in vitro. However, the enhancement of Ih by phasic, near-physiological, cAMP pulses was diminished by approximately 40% and the half-maximal cAMP concentration increased by approximately 5-fold. This decreased responsiveness of Ih to its major cellular modulator preceded epilepsy onset in GAERS, persisted throughout the chronic state, and was accompanied by an enhanced expression of the cAMP-insensitive HCN1 channel mRNA (> 50%), without changes in the mRNA levels of HCN2 and HCN4. To assess for alterations in TC cell excitability, we monitored the slow up-regulation of Ih that is induced by Ca2+-triggered cAMP synthesis and important for terminating in vitro synchronized oscillations. Remarkably, repetitive rebound Ca2+ spikes evoked normal slow Ih up-regulation in mature GAERS neurones; that sufficed to attenuate spontaneous rhythmic burst discharges. These adaptive mechanisms occurred upstream of cAMP turnover and involved enhanced intracellular Ca2+ accumulation upon repetitive low-threshold Ca2+ discharges. Therefore, HCN channels appear to play a dual role in epilepsy. Weakened cAMP binding to HCN channels precedes, and likely promotes, epileptogenesis in GAERS, whereas compensatory mechanisms stabilizing Ih function contribute to the termination of spike-and-wave discharges in chronic epilepsy.
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Affiliation(s)
- Mira Kuisle
- Department of Pharmacology and Neurobiology, Klingelbergstr. 70, CH-4056 Basel, Switzerland
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90
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Ivanova E, Müller F. Retinal bipolar cell types differ in their inventory of ion channels. Vis Neurosci 2006; 23:143-54. [PMID: 16638168 DOI: 10.1017/s0952523806232048] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2005] [Accepted: 01/20/2006] [Indexed: 11/06/2022]
Abstract
Bipolar cells were recorded in rat retinal slices to study the distribution of hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels. Patch-clamp whole cell measurements were combined with intracellular filling and recorded cells were morphologically identified. HCN channel isoforms HCN1-4 are differentially expressed in bipolar cells. Each bipolar cell type has a characteristic inventory of HCN channels. The combination of HCN channel currents and other voltage-gated currents can be used as a kind of “finger print” to electrophysiologically identify and classify bipolar cell types. Using this approach of combined electrophysiological and morphological classification we could identify a new ON-cone bipolar cell type.
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Affiliation(s)
- Elena Ivanova
- Institut für Biologische Informationsverarbeitung 1, Forschungszentrum Jülich, Jülich, Germany
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91
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Proenza C, Yellen G. Distinct populations of HCN pacemaker channels produce voltage-dependent and voltage-independent currents. ACTA ACUST UNITED AC 2006; 127:183-90. [PMID: 16446506 PMCID: PMC2151495 DOI: 10.1085/jgp.200509389] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Hyperpolarization-activated HCN pacemaker channels are critical for the generation of spontaneous activity and the regulation of excitability in the heart and in many types of neurons. These channels produce both a voltage-dependent current (Ih) and a voltage-independent current (Iinst or VIC). In this study, we explored the molecular basis of the voltage-independent current. We found that for the spHCN isoform, VIC averaged ∼4% of the maximum HCN conductance that could be activated by hyperpolarization. Cyclic AMP increased the voltage-independent current in spHCN to ∼8% of maximum. In HCN2, VIC was ∼2% of the maximal current, and was little affected by cAMP. VIC in both spHCN and HCN2 was blocked rapidly both by ZD7288 (an HCN channel blocker that is thought to bind in the conduction pore) and by application of Cd2+ to channels containing an introduced cysteine in the pore (spHCN-464C or HCN2-436C). These results suggest that VIC flows through the main conduction pathway, down the central axis of the protein. We suspected that VIC simply represented a nonzero limiting open probability for HCN channels at positive voltages. Surprisingly, we found instead that the spHCN channels carrying VIC were not in rapid equilibrium with the channels carrying the voltage-dependent current, because they could be blocked independently; a single application of blocker at a depolarized potential essentially eliminated VIC with little change in Ih. Thus, VIC appears to be produced by a distinct population of HCN channels. This voltage-independent current could contribute significantly to the role of HCN channels in neurons and myocytes; VIC flowing through the channels at physiological potentials would tend to promote excitability by accelerating both depolarization and repolarization.
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Affiliation(s)
- Catherine Proenza
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
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92
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Arinsburg SS, Cohen IS, Yu HG. Constitutively active Src tyrosine kinase changes gating of HCN4 channels through direct binding to the channel proteins. J Cardiovasc Pharmacol 2006; 47:578-86. [PMID: 16680072 PMCID: PMC1693968 DOI: 10.1097/01.fjc.0000211740.47960.8b] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Cardiac pacemaker current, if, is generated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. Our previous studies demonstrated that altered tyrosine phosphorylation can modulate the properties of both if and HCN channels. To assess a hypothesis that the intracellular tyrosine kinase Src may play a role in modulation by tyrosine phosphorylation of if, we cotransfected HEK293 cells with HCN4 and Src proteins. When HCN4 was cotransfected with a constitutively activated Src protein (Src529), the resultant voltage-dependent HCN4 activation was positively shifted (HCN4: V1/2 = -93 mV; Src529: V1/2 = -80 mV). The activation kinetics were accelerated at some potentials but not over the entire voltage range tested (eg, at -95 mV, tau_act(HCN4) = 3,243 ms; tau_act(Src529) = 1,113 ms). When HCN4 was cotransfected with a dominant negative Src protein (Src296), the HCN4 activation was shifted more negative to a smaller degree (HCN4: V1/2 = -93 mV; Src296: V1/2 = -98 mV; statistically insignificant) and the activation kinetics were slowed at most test potentials (eg, at -95 mV, tau_act(Src296) = 7,396 ms). Neither Src529 nor Src296 significantly altered HCN4 current density. Coimmunoprecipitation experiments revealed that Src forms a complex with HCN4 in HEK293 cells and in rat ventricular myocytes. Our data provide a novel mechanism of if regulation by Src tyrosine phosphorylation.
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Affiliation(s)
- Suzanne S. Arinsburg
- From the New York College of Osteopathic Medicine of the New York Institute of Technology, NY
| | - Ira S. Cohen
- From the Institute of Molecular Cardiology and Department of Physiology & Biophysics, State University of New York at Stony Brook, Stony Brook, NY
| | - Han-Gang Yu
- From the New York College of Osteopathic Medicine of the New York Institute of Technology, NY
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93
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Milligan CJ, Edwards IJ, Deuchars J. HCN1 ion channel immunoreactivity in spinal cord and medulla oblongata. Brain Res 2006; 1081:79-91. [PMID: 16503331 DOI: 10.1016/j.brainres.2006.01.019] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2005] [Revised: 01/05/2006] [Accepted: 01/09/2006] [Indexed: 11/27/2022]
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) non-selective cation channels in neurons carry currents proposed to perform diverse functions, including the hyperpolarization activated Ih current. The 4 HCN subunits have unique but overlapping patterns of expression in the CNS. Here, we examined the distribution of HCN1 channel subunits in the brainstem and spinal cord using immunohistochemistry. At all levels of the spinal cord dorsal horn, HCN1 immunoreactivity (HCN1-IR) was predominantly absent from laminae I and II, while a dense band of punctate labeling was visible in lamina III. Labeled neurons were identified in close vicinity to the central canal, in the lateral spinal nucleus, in the ventral horn and occasionally in lamina II and III. Those in the ventral horn were identified as alpha motor neurons using retrograde tracing and/or double or triple immunostaining with neuronal markers neurofilament 200 (NF200) and choline acetyltransferase. HCN1-IR neurons in the brainstem included neurons in sensory pathways such as the dorsal column nuclei, the area postrema, the spinal trigeminal nucleus as well as identified motor neurons in motor nuclei. In the nucleus ambiguus, a mixed visceral/motor nucleus, HCN1-IR was present only in NF200-IR cells, suggesting that it is expressed in motor but not autonomic preganglionic neurons. HCN1-IR motor neurons in the nucleus ambiguus also expressed the neurokinin 1 receptor and were labeled retrogradely from the larnyx. At the light microscopic level, the NTS and inferior olive contained punctate labeling, which ultrastructural examination revealed to be present in predominantly synaptic terminals or dendrites respectively. These data therefore described the first localization of the HCN1 subunit in the spinal cord and extend previous reports from the brainstem.
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Affiliation(s)
- Carol J Milligan
- Institute of Membrane and Systems Biology, University of Leeds, LS2 9JT, UK
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94
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Roepke TK, Abbott GW. Pharmacogenetics and cardiac ion channels. Vascul Pharmacol 2006; 44:90-106. [PMID: 16344000 DOI: 10.1016/j.vph.2005.07.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2005] [Accepted: 07/01/2005] [Indexed: 12/19/2022]
Abstract
Ion channels control electrical excitability in living cells. In mammalian heart, the opposing actions of Na(+) and Ca(2+) ion influx, and K(+) ion efflux, through cardiac ion channels determine the morphology and duration of action potentials in cardiac myocytes, thus controlling the heartbeat. The last decade has seen a leap in our understanding of the molecular genetic origins of inherited cardiac arrhythmia, largely through identification of mutations in cardiac ion channels and the proteins that regulate them. Further, recent advances have shown that 'acquired arrhythmias', which occur more commonly than inherited arrhythmias, arise due to a variety of environmental factors including side effects of therapeutic drugs and often have a significant genetic component. Here, we review the pharmacogenetics of cardiac ion channels-the interplay between genetic and pharmacological factors that underlie human cardiac arrhythmias.
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Affiliation(s)
- Torsten K Roepke
- Greenberg Division of Cardiology, Department of Medicine, Cornell University, Weill Medical College, 520 East 70th Street, New York, NY 10021, USA
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95
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Jespersen T, Grunnet M, Rasmussen HB, Jørgensen NB, Jensen HS, Angelo K, Olesen SP, Klaerke DA. The corticosteroid hormone induced factor: a new modulator of KCNQ1 channels? Biochem Biophys Res Commun 2006; 341:979-88. [PMID: 16476578 DOI: 10.1016/j.bbrc.2006.01.046] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2006] [Accepted: 01/11/2006] [Indexed: 10/25/2022]
Abstract
The corticosteroid hormone induced factor (CHIF) is a member of the one-transmembrane segment protein family named FXYD, which also counts phospholemman and the Na,K-pump gamma-subunit. Originally it was suggested that CHIF could induce the expression of the I(Ks) current when expressed in Xenopus laevis oocytes, but recently CHIF has attracted attention as a modulatory subunit of the Na,K-pump. In renal and intestinal epithelia, the expression of CHIF is dramatically up-regulated in response to aldosterone stimulation, and regulation of epithelial ion channels by CHIF is an attractive hypothesis. To study a potential regulatory effect of the CHIF subunit on KCNQ1 channels, co-expression experiments were performed in Xenopus laevis oocytes and mammalian CHO-K1 cells. Electrophysiological characterization was obtained by two-electrode voltage-clamp and patch-clamp, respectively. In both expression systems, we find that CHIF drastically modulates the KCNQ1 current; in the presence of CHIF, the KCNQ1 channels open at all membrane potentials. Thereby, CHIF is the first accessory subunit shown to be capable of modulating both the Na,K-pump and an ion channel. To find a possible physiological function of the constitutively open KCNQ1/CHIF complex, the precise localization of KCNQ1 and CHIF in distal colon and kidney from control and salt-depleted rats was determined by confocal microscopy. However, in these tissues, we did not detect an obvious overlap in expression between KCNQ1 and CHIF. In conclusion, the hormone-regulated subunit CHIF modulates the voltage sensitivity of the KCNQ channels, but so far evidence for an actual co-localization of CHIF and KCNQ1 channels in native tissue is lacking.
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Affiliation(s)
- Thomas Jespersen
- Department of Medical Physiology and Danish Arrhythmia Research Centre, The Panum Institute, Blegdamsvej 3, DK-2200 Copenhagen, Denmark
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96
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Budde T, Caputi L, Kanyshkova T, Staak R, Abrahamczik C, Munsch T, Pape HC. Impaired regulation of thalamic pacemaker channels through an imbalance of subunit expression in absence epilepsy. J Neurosci 2006; 25:9871-82. [PMID: 16251434 PMCID: PMC6725576 DOI: 10.1523/jneurosci.2590-05.2005] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The role of hyperpolarization-activated, cyclic nucleotide-modulated (HCN) channel isoforms and hyperpolarization-activated cation current (Ih) for seizure-related burst firing in thalamocortical (TC) neurons was investigated in a rat genetic model of absence epilepsy [Wistar Albino Glaxo rats, bred in Rijswijk (WAG/Rij)]. Burst discharges in TC neurons locked to seizure activity in vivo were prolonged during blockade of Ih by Cs+ and ZD7288 (4-ethylphenylamino-1,2-dimethyl-6-methylaminopyrimidinium chloride). In vitro analyses revealed a hyperpolarizing shift of half-maximal Ih activation (Vh) in WAG/Rij (Vh = -93.2 mV) compared with nonepileptic controls [August x Copenhagen-Irish (ACI) (Vh = -88.0 mV)]. This effect is explained by a shift of the responsiveness of Ih to cAMP toward higher concentrations in TC neurons from WAG/Rij, as revealed by application of 8-bromo-cAMP and the phosphodiesterase inhibitor IBMX. During blockade of adenylyl cyclase activity, Ih activation was similar in the two strains, whereas the difference in cAMP responsiveness persisted, thereby voting against different ambient cAMP levels between strains. Increasing the intracellular cAMP level and shifting Ih activation led to a change from burst to tonic firing mode in WAG/Rij but not in ACI rats. Furthermore, HCN1 expression was significantly increased on mRNA and protein levels, with no changes in HCN2-4 expression. In conclusion, there is an increase in HCN1 expression in the epileptic thalamus, associated with a decrease in cAMP responsiveness of Ih in TC neurons and resulting impairment to control the shift from burst to tonic firing, which, in turn, will prolong burst activity after recruitment of Ih during absence seizures.
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MESH Headings
- 1-Methyl-3-isobutylxanthine/pharmacology
- 8-Bromo Cyclic Adenosine Monophosphate/pharmacology
- Action Potentials/drug effects
- Adenine/analogs & derivatives
- Adenine/pharmacology
- Animals
- Blotting, Northern/methods
- Cerebral Cortex/cytology
- Cesium/pharmacology
- Chlorides/pharmacology
- Cyclic Nucleotide-Gated Cation Channels
- Disease Models, Animal
- Dose-Response Relationship, Drug
- Dose-Response Relationship, Radiation
- Drug Interactions
- Electric Stimulation/methods
- Electroencephalography/methods
- Enzyme Inhibitors/pharmacology
- Epilepsy, Absence/genetics
- Epilepsy, Absence/metabolism
- Epilepsy, Absence/physiopathology
- Female
- Gene Expression Regulation/drug effects
- Gene Expression Regulation/physiology
- Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
- Immunohistochemistry/methods
- In Situ Hybridization/methods
- In Vitro Techniques
- Ion Channels/metabolism
- Male
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Membrane Potentials/radiation effects
- Microinjections
- Neurons/metabolism
- Patch-Clamp Techniques/methods
- Potassium Channels
- Protein Isoforms/metabolism
- Pyrimidines/pharmacology
- RNA, Messenger/biosynthesis
- Rats
- Rats, Mutant Strains
- Rats, Wistar
- Reverse Transcriptase Polymerase Chain Reaction/methods
- Thalamus/cytology
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Affiliation(s)
- Thomas Budde
- Institut für Experimentelle Epilepsieforschung, Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany
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97
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Simeone TA, Rho JM, Baram TZ. Single channel properties of hyperpolarization-activated cation currents in acutely dissociated rat hippocampal neurones. J Physiol 2005; 568:371-80. [PMID: 16123099 PMCID: PMC1474727 DOI: 10.1113/jphysiol.2005.093161] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 06/21/2005] [Accepted: 08/04/2005] [Indexed: 11/08/2022] Open
Abstract
The hyperpolarization-activated cation current (I(h)), mediated by HCN channels, contributes to intrinsic neuronal properties, synaptic integration and network rhythmicity. Recent studies have implicated HCN channels in neuropathological conditions including epilepsy. While native HCN channels have been studied at the macroscopic level, the biophysical characteristics of individual neuronal HCN channels have not been described. We characterize, for the first time, single HCN currents of excised inside-out patches from somata of acutely dissociated rat hippocampal CA1 pyramidal cells. Hyperpolarization steps elicited non-inactivating channel openings with an apparent conductance of 9.7 pS, consistent with recent reports of native and recombinant HCN channels. The voltage-dependent P(o) had a V(1/2) of -81 +/- 1.8 mV and slope -13.3 +/- 1.9 mV. Blockers of macroscopic I(h), ZD7288 (50 microM) and CsCl (1 mM), reduced the channel conductance to 8 pS and 8.4 pS, respectively. ZD7288 was slightly more effective in reducing the P(o) at depolarized potentials, whereas CsCl was more efficacious at hyperpolarized potentials. The unitary neuronal HCN channels had voltage-dependent latencies to first channel opening and two open states. As expected, ZD7288 and CsCl increased latencies and decreased the properties of both open states. The major endogenous positive modulator of macroscopic I(h) is cAMP. Application of 8Br-cAMP (10 microM) did not affect conductance (9.4 pS), but did increase P(o) and short and long open times. Thus, sensitivity to I(h) modulators supports the single h-channel identity of these unitary currents. Detailed biophysical analysis of unitary I(h) conductances is likely to help distinguish between homomeric and heteromeric expression of these channels - findings that may be relevant toward the pathophysiology of diseases such as epilepsy.
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Affiliation(s)
- T A Simeone
- Department of Anatomy and Neurobiology, University of California, Irvine, 92697, USA
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98
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Zong X, Eckert C, Yuan H, Wahl-Schott C, Abicht H, Fang L, Li R, Mistrik P, Gerstner A, Much B, Baumann L, Michalakis S, Zeng R, Chen Z, Biel M. A novel mechanism of modulation of hyperpolarization-activated cyclic nucleotide-gated channels by Src kinase. J Biol Chem 2005; 280:34224-32. [PMID: 16079136 DOI: 10.1074/jbc.m506544200] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated channels (HCN1-4) play a crucial role in the regulation of cell excitability. Importantly, they contribute to spontaneous rhythmic activity in brain and heart. HCN channels are principally activated by membrane hyperpolarization and binding of cAMP. Here, we identify tyrosine phosphorylation by Src kinase as another mechanism affecting channel gating. Inhibition of Src by specific blockers slowed down activation kinetics of native and heterologously expressed HCN channels. The same effect on HCN channel activation was observed in cells cotransfected with a dominant-negative Src mutant. Immunoprecipitation demonstrated that Src binds to and phosphorylates native and heterologously expressed HCN2. Src interacts via its SH3 domain with a sequence of HCN2 encompassing part of the C-linker and the cyclic nucleotide binding domain. We identified a highly conserved tyrosine residue in the C-linker of HCN channels (Tyr476 in HCN2) that confers modulation by Src. Replacement of this tyrosine by phenylalanine in HCN2 or HCN4 abolished sensitivity to Src inhibitors. Mass spectrometry confirmed that Tyr476 is phosphorylated by Src. Our results have functional implications for HCN channel gating. Furthermore, they indicate that tyrosine phosphorylation contributes in vivo to the fine tuning of HCN channel activity.
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Affiliation(s)
- Xiangang Zong
- Department Pharmazie, Pharmakologie für Naturwissenschaften, Ludwig-Maximilians Universität München, Butenandtstrasse 7, 81377 München
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99
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McPate MJ, Duncan RS, Milnes JT, Witchel HJ, Hancox JC. The N588K-HERG K+ channel mutation in the ‘short QT syndrome’: Mechanism of gain-in-function determined at 37°C. Biochem Biophys Res Commun 2005; 334:441-9. [PMID: 16011830 DOI: 10.1016/j.bbrc.2005.06.112] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2005] [Accepted: 06/21/2005] [Indexed: 11/24/2022]
Abstract
The idiopathic short QT syndrome (SQTS) is characterised by an abnormally short QT interval on the electrocardiogram and by an increased risk of arrhythmia and sudden death. One variant of the syndrome is linked to missense mutations that lead to a single amino-acid change (N588K; asparagine to lysine) in the S5-Pore linker region of the cardiac HERG K(+) channel. This study was performed in order to determine how the N588K mutation alters HERG channel current (I(HERG)) kinetics at mammalian physiological temperature. The whole-cell current-voltage (I-V) relation for wild-type (WT) I(HERG) measured from Chinese Hamster Ovary cells was maximal at approximately 0 mV and showed marked inward rectification positive to this. In contrast, N588K I(HERG) showed marked rectification only at +60 mV and at more positive voltages. The voltage dependence of activation of N588K-HERG did not differ significantly from that of WT-HERG. However, N588K I(HERG) had a significantly more positive inactivation V(0.5) (-8.14+/-0.82 mV) than did WT I(HERG) (-70.05+/-0.82 mV; P<0.001, unpaired t test; n=5 for each). Its P(Na)/P(K) ratio was also greater. The instantaneous I-V relation for N588K I(HERG) under action potential voltage clamp peaked at approximately +40 mV, compared to approximately -37 mV for WT-I(HERG). These findings underscore the importance of the S5-P linker in HERG channel function and indicate that N588K-HERG contributes increased repolarising current earlier in the ventricular action potential at physiological temperature due to a approximately +60 mV shift in voltage dependence of I(HERG) inactivation.
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Affiliation(s)
- Mark J McPate
- Department of Physiology and Cardiovascular Research Laboratories, School of Medical Sciences, University Walk, Bristol BS8 1TD, UK
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100
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Baruscotti M, Bucchi A, Difrancesco D. Physiology and pharmacology of the cardiac pacemaker (“funny”) current. Pharmacol Ther 2005; 107:59-79. [PMID: 15963351 DOI: 10.1016/j.pharmthera.2005.01.005] [Citation(s) in RCA: 245] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2005] [Accepted: 01/26/2005] [Indexed: 12/19/2022]
Abstract
First described over a quarter of a century ago, the cardiac pacemaker "funny" (I(f)) current has been extensively characterized since, and its role in cardiac pacemaking has been thoroughly demonstrated. A similar current, termed I(h), was later described in different types of neurons, where it has a variety of functions and contributes to the control of cell excitability and plasticity. I(f) is an inward current activated by both voltage hyperpolarization and intracellular cAMP. In the heart, as well as generating spontaneous activity, f-channels mediate autonomic-dependent modulation of heart rate: beta-adrenergic stimulation accelerates, and vagal stimulation slows, cardiac rate by increasing and decreasing, respectively, the intracellular cAMP concentration and, consequently, the f-channel degree of activation. Four isoforms of hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels have been cloned more recently and shown to be the molecular correlates of native f-channels in the heart and h-channels in the brain. Individual HCN isoforms have kinetic and modulatory properties which differ quantitatively. A comparison of their biophysical properties with those of native pacemaker channels provides insight into the molecular basis of the pacemaker current properties and, together with immunolabelling and other detection techniques, gives information on the pattern of HCN isoform distribution in different tissues. Because of their relevance to cardiac pacemaker activity, f-channels are a natural target of drugs aimed at the pharmacological control of heart rate. Several agents developed for their ability to selectively reduce heart rate act by a specific inhibition of f-channel function; these substances have a potential for the treatment of diseases such as angina and heart failure. In the near future, devices based on the delivery of f-channels in situ, or of a cellular source of f-channels (biological pacemakers), will likely be developed for use in therapies for diseases of heart rhythm with the aim of replacing electronic pacemakers.
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Affiliation(s)
- Mirko Baruscotti
- Laboratory of Molecular Physiology and Neurobiology, Department of Biomolecular Sciences and Biotechnology, University of Milano, via Celoria 26, 20133 Milan, Italy
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