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Hennis K, Piantoni C, Biel M, Fenske S, Wahl-Schott C. Pacemaker Channels and the Chronotropic Response in Health and Disease. Circ Res 2024; 134:1348-1378. [PMID: 38723033 PMCID: PMC11081487 DOI: 10.1161/circresaha.123.323250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 05/13/2024]
Abstract
Loss or dysregulation of the normally precise control of heart rate via the autonomic nervous system plays a critical role during the development and progression of cardiovascular disease-including ischemic heart disease, heart failure, and arrhythmias. While the clinical significance of regulating changes in heart rate, known as the chronotropic effect, is undeniable, the mechanisms controlling these changes remain not fully understood. Heart rate acceleration and deceleration are mediated by increasing or decreasing the spontaneous firing rate of pacemaker cells in the sinoatrial node. During the transition from rest to activity, sympathetic neurons stimulate these cells by activating β-adrenergic receptors and increasing intracellular cyclic adenosine monophosphate. The same signal transduction pathway is targeted by positive chronotropic drugs such as norepinephrine and dobutamine, which are used in the treatment of cardiogenic shock and severe heart failure. The cyclic adenosine monophosphate-sensitive hyperpolarization-activated current (If) in pacemaker cells is passed by hyperpolarization-activated cyclic nucleotide-gated cation channels and is critical for generating the autonomous heartbeat. In addition, this current has been suggested to play a central role in the chronotropic effect. Recent studies demonstrate that cyclic adenosine monophosphate-dependent regulation of HCN4 (hyperpolarization-activated cyclic nucleotide-gated cation channel isoform 4) acts to stabilize the heart rate, particularly during rapid rate transitions induced by the autonomic nervous system. The mechanism is based on creating a balance between firing and recently discovered nonfiring pacemaker cells in the sinoatrial node. In this way, hyperpolarization-activated cyclic nucleotide-gated cation channels may protect the heart from sinoatrial node dysfunction, secondary arrhythmia of the atria, and potentially fatal tachyarrhythmia of the ventricles. Here, we review the latest findings on sinoatrial node automaticity and discuss the physiological and pathophysiological role of HCN pacemaker channels in the chronotropic response and beyond.
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Affiliation(s)
- Konstantin Hennis
- Institute of Cardiovascular Physiology and Pathophysiology, Biomedical Center Munich, Walter Brendel Centre of Experimental Medicine, Faculty of Medicine (K.H., C.P., C.W.-S.), Ludwig-Maximilians-Universität München, Germany
| | - Chiara Piantoni
- Institute of Cardiovascular Physiology and Pathophysiology, Biomedical Center Munich, Walter Brendel Centre of Experimental Medicine, Faculty of Medicine (K.H., C.P., C.W.-S.), Ludwig-Maximilians-Universität München, Germany
| | - Martin Biel
- Department of Pharmacy, Center for Drug Research (M.B., S.F.), Ludwig-Maximilians-Universität München, Germany
- German Centre for Cardiovascular Research (DZHK), Partner Site Munich Heart Alliance, Germany (M.B., S.F.)
| | - Stefanie Fenske
- Department of Pharmacy, Center for Drug Research (M.B., S.F.), Ludwig-Maximilians-Universität München, Germany
- German Centre for Cardiovascular Research (DZHK), Partner Site Munich Heart Alliance, Germany (M.B., S.F.)
| | - Christian Wahl-Schott
- Institute of Cardiovascular Physiology and Pathophysiology, Biomedical Center Munich, Walter Brendel Centre of Experimental Medicine, Faculty of Medicine (K.H., C.P., C.W.-S.), Ludwig-Maximilians-Universität München, Germany
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The Effect of the Tongyang Huoxue Recipe (TYHX) on the I to/ I Kur in Ischemia/Reperfusion Sinoatrial Node Cells. Cardiovasc Ther 2022; 2022:4114817. [PMID: 36605374 PMCID: PMC9794430 DOI: 10.1155/2022/4114817] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Revised: 09/26/2022] [Accepted: 11/23/2022] [Indexed: 12/24/2022] Open
Abstract
Background The transient outward potassium current (I to) and the ultrarapid delayed rectifier potassium current (I Kur) are major potassium currents involved in the repolarization process of sinoatrial node cells (SNCs). Methods and Results The SNCs of neonatal rats were divided into control, ischemia/reperfusion (I/R), I/R+blank serum, and Tongyang Huoxue recipe (TYHX) serum groups. I to and I Kur were recorded using the whole cell patch-clamp technique, and the current-voltage (I-V), steady-state activation (SSA), steady-state inactivation (SSI), and recovery from inactivation (RFI) curves were plotted, respectively. Compared to the control group, both the peak current density and the current density at the voltage of I to and I Kur decreased obviously in SNCs after simulated I/R, the SSA curves moved right, and the SSI curves moved left. After TYHX was added to the extracellular solution of SNCs, both the peak current density and the current density at the voltage of I to and I Kur increased significantly, the SSA curves moved left, and the SSI curves moved right with a significant difference of V 1/2. The recovery from the I Kur RFI curves was slightly restored, and the I to curves did not change. Conclusions TYHX increases the peak current density, accelerates the activation, and decreases the inactivation of the I to and I Kur. This may be the mechanism of TYHX in shortening the action potential duration of repolarization, which accelerates spontaneous pulsation.
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Kodirov SA, Brachmann J, Safonova TA, Zhuravlev VL. Inactivation of Native K Channels. J Membr Biol 2021; 255:13-31. [PMID: 34383081 DOI: 10.1007/s00232-021-00195-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2021] [Accepted: 06/30/2021] [Indexed: 01/12/2023]
Abstract
We have experimented with isolated cardiomyocytes of mollusks Helix. During the whole-cell patch-clamp recordings of K+ currents a considerable decrease in amplitude was observed upon repeated voltage steps at 0.96 Hz. For these experiments, ventricular cells were depolarized to identical + 20 mV from a holding potential of - 50 mV. The observed spontaneous inhibition of outward currents persisted in the presence of 4-aminopyridine, tetraethylammonium chloride or E-4031, the selective class III antiarrhythmic agent that blocks HERG channels. Similar tendency was retained when components of currents sensitive to either 4-AP or TEA were mathematically subtracted. Waveforms of currents sensitive to 1 and 10 micromolar concentration of E-4031 were distinct comprising prevailingly those activated during up to 200 ms pulses. The outward current activated by a voltage ramp at 60 mV x s-1 rate revealed an inward rectification around + 20 mV. This feature closely resembles those of the mammalian cardiac delayed rectifier IKr.
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Affiliation(s)
- Sodikdjon A Kodirov
- Department of Cardiology, Medical University Hospital Heidelberg, 69120, Heidelberg, Germany. .,Department of General Physiology, Saint Petersburg University, 199034, Saint Petersburg, Russia. .,Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, 02115, USA. .,Department of Biophysics, Saint Petersburg University, 199034, Saint Petersburg, Russia. .,Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Avenida Professor Egas Moniz, 1649-028, Lisboa, Portugal.
| | - Johannes Brachmann
- Department of Cardiology, Medical University Hospital Heidelberg, 69120, Heidelberg, Germany
| | - Tatiana A Safonova
- Department of General Physiology, Saint Petersburg University, 199034, Saint Petersburg, Russia
| | - Vladimir L Zhuravlev
- Department of Cardiology, Medical University Hospital Heidelberg, 69120, Heidelberg, Germany.,Department of General Physiology, Saint Petersburg University, 199034, Saint Petersburg, Russia
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Golovko V, Gonotkov M, Lebedeva E. Effects of 4-aminopyridine on action potentials generation in mouse sinoauricular node strips. Physiol Rep 2015; 3:3/7/e12447. [PMID: 26156968 PMCID: PMC4552527 DOI: 10.14814/phy2.12447] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The physiological role of Ito has yet to be clarified. The goal of this study is to investigate the possible contribution of the transient outward current (Ito) on the generation of transmembrane action potentials (APs) and the sensitivity of mouse sinoauricular node (SAN) cells to a 4-aminopyridine (4AP) as Ito blocker. The electrophysiological identification of cells was performed in the sinoauricular node artery area (nstrips = 38) of the subendocardial surface using microelectrode technique. In this study, for the first time, it was observed that dependence duration of action potential at the level of 20% repolarization (APD20) level under a 4AP concentration in the pacemaker SAN and auricular cells corresponds to a curve predicted by Hill's equation. APD20 raised by 70% and spike duration of AP increased by 15-25%, when 4AP concentration was increased from 0.1 to 5.0 mmol/L. Auricular cells were found to be more sensitive to 4AP than true pacemaker cells. This was accompanied by a decrease in the upstroke velocity as compared to the control. Our data and previous findings in the literature lead us to hypothesize that the 4AP-sensitive current participates in the repolarization formation of pacemaker and auricular type cells. Thus, study concerning the inhibitory effects of lidocaine and TTX on APD20 can explain the phenomenon of the decrease in upstroke velocity, which, for the first time, was observed after exposure to 4AP. Duration of AP at the level of 20% repolarization (APD20) under a 4-AP concentration 0.5 mmol/L in the true pacemaker cells lengthen by 60-70% with a control.
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Affiliation(s)
- Vladimir Golovko
- Laboratory of Heart Physiology, Institute of Physiology, Komi Science Center, The Urals Branch of the Russian Academy of Sciences, Syktyvkar, Russia
| | - Mikhail Gonotkov
- Laboratory of Heart Physiology, Institute of Physiology, Komi Science Center, The Urals Branch of the Russian Academy of Sciences, Syktyvkar, Russia
| | - Elena Lebedeva
- Laboratory of Heart Physiology, Institute of Physiology, Komi Science Center, The Urals Branch of the Russian Academy of Sciences, Syktyvkar, Russia
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Aminopyridine lengthened the plateau phase of action potentials in mouse sinoatrial node cells. Bull Exp Biol Med 2013; 156:4-6. [PMID: 24319724 DOI: 10.1007/s10517-013-2263-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Duration of the plateau phase (phase 2) of action potentials in pacemaker cells in mouse sinoatrial node characterized by low upstroke rate during the rapid depolarization (dV/dt max <7 V/sec, phase 0) and in atrial-like cells with dV/dt max <100 V/sec were prolonged by 50% with 4-aminopyridine in concentrations of 0.7 and 0.1 mM, respectively. This blocker did not lengthen the terminal repolarization (phase 3). The above changes were accompanied by a 20-80% decrease in dV/dt max in comparison to the control. It is hypothesized that the short-term (transient) outward current Ito takes a part in the plateau formation and modulates the duration of the rapid depolarization phase of action potentials in mouse sinoatrial node cells.
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7
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SEM, TEM, and IHC Analysis of the Sinus Node and Its Implications for the Cardiac Conduction System. ANATOMY RESEARCH INTERNATIONAL 2013; 2013:961459. [PMID: 24282640 PMCID: PMC3825050 DOI: 10.1155/2013/961459] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/09/2013] [Revised: 09/12/2013] [Accepted: 09/17/2013] [Indexed: 11/17/2022]
Abstract
More than 100 years after the discovery of the sinus node (SN) by Keith and Flack, the function and structure of the SN have not been completely established yet. The anatomic architecture of the SN has often been described as devoid of an organized structure; the origin of the sinus impulse is still a matter of debate, and a definite description of the long postulated internodal specialized tract conducting the impulse from the SN to the atrioventricular node (AVN) is still missing. In our previously published study, we proposed a morphologically ordered structure for the SN. As a confirmation of what was presented then, we have added the results of additional observations regarding the structural particularities of the SN. We investigated the morphology of the sinus node in the human hearts of healthy individuals using histochemical, immunohistochemical, optical, and electron microscopy (SEM, TEM). Our results confirmed that the SN presents a previously unseen highly organized architecture.
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Allah EA, Tellez JO, Yanni J, Nelson T, Monfredi O, Boyett MR, Dobrzynski H. Changes in the expression of ion channels, connexins and Ca2+-handling proteins in the sino-atrial node during postnatal development. Exp Physiol 2011; 96:426-38. [DOI: 10.1113/expphysiol.2010.055780] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Brahmajothi MV, Morales MJ, Campbell DL, Steenbergen C, Strauss HC. Expression and distribution of voltage-gated ion channels in ferret sinoatrial node. Physiol Genomics 2010; 42A:131-40. [PMID: 20682846 DOI: 10.1152/physiolgenomics.00049.2010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Spontaneous diastolic depolarization in the sinoatrial (SA) node enables it to serve as pacemaker of the heart. The variable cell morphology within the SA node predicts that ion channel expression would be heterogeneous and different from that in the atrium. To evaluate ion channel heterogeneity within the SA node, we used fluorescent in situ hybridization to examine ion channel expression in the ferret SA node region and atrial appendage. SA nodal cells were distinguished from surrounding cardiac myocytes by expression of the slow (SA node) and cardiac (surrounding tissue) forms of troponin I. Nerve cells in the sections were identified by detection of GAP-43 and cytoskeletal middle neurofilament. Transcript expression was characterized for the 4 hyperpolarization-activated cation channels, 6 voltage-gated Na(+) channels, 3 voltage-gated Ca(2+) channels, 24 voltage-gated K(+) channel α-subunits, and 3 ancillary subunits. To ensure that transcript expression was representative of protein expression, immunofluorescence was used to verify localization patterns of voltage-dependent K(+) channels. Colocalizations were performed to observe any preferential patterns. Some overlapping and nonoverlapping binding patterns were observed. Measurement of different cation channel transcripts showed heterogeneous expression with many different patterns of expression, attesting to the complexity of electrical activity in the SA node. This study provides insight into the possible role ion channel heterogeneity plays in SA node pacemaker activity.
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Affiliation(s)
- Mulugu V Brahmajothi
- Division of Neonatology, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
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Niwa N, Nerbonne JM. Molecular determinants of cardiac transient outward potassium current (I(to)) expression and regulation. J Mol Cell Cardiol 2009; 48:12-25. [PMID: 19619557 DOI: 10.1016/j.yjmcc.2009.07.013] [Citation(s) in RCA: 161] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2009] [Revised: 06/25/2009] [Accepted: 07/10/2009] [Indexed: 12/21/2022]
Abstract
Rapidly activating and inactivating cardiac transient outward K(+) currents, I(to), are expressed in most mammalian cardiomyocytes, and contribute importantly to the early phase of action potential repolarization and to plateau potentials. The rapidly recovering (I(t)(o,f)) and slowly recovering (I(t)(o,s)) components are differentially expressed in the myocardium, contributing to regional heterogeneities in action potential waveforms. Consistent with the marked differences in biophysical properties, distinct pore-forming (alpha) subunits underlie the two I(t)(o) components: Kv4.3/Kv4.2 subunits encode I(t)(o,f), whereas Kv1.4 encodes I(t)(o,s), channels. It has also become increasingly clear that cardiac I(t)(o) channels function as components of macromolecular protein complexes, comprising (four) Kvalpha subunits and a variety of accessory subunits and regulatory proteins that influence channel expression, biophysical properties and interactions with the actin cytoskeleton, and contribute to the generation of normal cardiac rhythms. Derangements in the expression or the regulation of I(t)(o) channels in inherited or acquired cardiac diseases would be expected to increase the risk of potentially life-threatening cardiac arrhythmias. Indeed, a recently identified Brugada syndrome mutation in KCNE3 (MiRP2) has been suggested to result in increased I(t)(o,f) densities. Continued focus in this area seems certain to provide new and fundamentally important insights into the molecular determinants of functional I(t)(o) channels and into the molecular mechanisms involved in the dynamic regulation of I(t)(o) channel functioning in the normal and diseased myocardium.
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Affiliation(s)
- Noriko Niwa
- Department of Developmental Biology, Washington University School of Medicine, 660 South Euclid Avenue, Box 8103, St. Louis, MO 63110-1093, USA
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Greener ID, Tellez JO, Dobrzynski H, Yamamoto M, Graham GM, Billeter R, Boyett MR. Ion Channel Transcript Expression at the Rabbit Atrioventricular Conduction Axis. Circ Arrhythm Electrophysiol 2009; 2:305-15. [DOI: 10.1161/circep.108.803569] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Background—
Little is known about the distribution of gap junctions and ion channels in the atrioventricular node, even though the physiology and pathology of the atrioventricular node is ultimately dependent on them.
Methods and Results—
The abundance of 30 transcripts for markers, gap junctions, ion channels, and Ca
2+
-handling proteins in different regions of the rabbit atrioventricular node (nodal extension and proximal and distal penetrating bundle of His as well as atrial and ventricular muscle) was measured using a novel quantitative polymerase chain reaction technique and in situ hybridization. The expression profile of the nodal extension (slow pathway into penetrating bundle) was similar to that of the sinoatrial node. For example, in the nodal extension, in contrast to the atrial muscle and as expected for a slowly conducting tissue with pacemaker activity, there was no or reduced expression of Cx43, Na
v
1.5, Ca
v
1.2, K
v
1.4, KChIP2, and RYR3 and high expression of Ca
v
1.3 and HCN4. The expression profile of the penetrating bundle was less specialized. In situ hybridization revealed a transitional zone with reduced expression of Cx43, Na
v
1.5, and KChIP2 that may form the fast pathway into the penetrating bundle.
Conclusions—
At the atrioventricular node, the expression of gap junctions and ion channels in the nodal extension (slow pathway) and a transitional zone (putative fast pathway) as well as the penetrating bundle (output pathway) is specialized and heterogeneous and roughly matches the electrophysiology of the different regions.
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Affiliation(s)
- Ian D. Greener
- From the Cardiovascular Research Group (I.D.G., J.O.T., H.D., M.R.B.), Faculty of Medical and Human Sciences, University of Manchester, Core Technology Facility, Manchester, United Kingdom; the Department of Circulation (M.Y.), Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan; Institute of Membrane and Systems Biology (G.M.G.), University of Leeds, Leeds, United Kingdom; and Centre for Integrated Systems Biology (R.B.), University of Nottingham, Nottingham, United Kingdom
| | - James O. Tellez
- From the Cardiovascular Research Group (I.D.G., J.O.T., H.D., M.R.B.), Faculty of Medical and Human Sciences, University of Manchester, Core Technology Facility, Manchester, United Kingdom; the Department of Circulation (M.Y.), Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan; Institute of Membrane and Systems Biology (G.M.G.), University of Leeds, Leeds, United Kingdom; and Centre for Integrated Systems Biology (R.B.), University of Nottingham, Nottingham, United Kingdom
| | - Halina Dobrzynski
- From the Cardiovascular Research Group (I.D.G., J.O.T., H.D., M.R.B.), Faculty of Medical and Human Sciences, University of Manchester, Core Technology Facility, Manchester, United Kingdom; the Department of Circulation (M.Y.), Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan; Institute of Membrane and Systems Biology (G.M.G.), University of Leeds, Leeds, United Kingdom; and Centre for Integrated Systems Biology (R.B.), University of Nottingham, Nottingham, United Kingdom
| | - Mitsuru Yamamoto
- From the Cardiovascular Research Group (I.D.G., J.O.T., H.D., M.R.B.), Faculty of Medical and Human Sciences, University of Manchester, Core Technology Facility, Manchester, United Kingdom; the Department of Circulation (M.Y.), Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan; Institute of Membrane and Systems Biology (G.M.G.), University of Leeds, Leeds, United Kingdom; and Centre for Integrated Systems Biology (R.B.), University of Nottingham, Nottingham, United Kingdom
| | - Gillian M. Graham
- From the Cardiovascular Research Group (I.D.G., J.O.T., H.D., M.R.B.), Faculty of Medical and Human Sciences, University of Manchester, Core Technology Facility, Manchester, United Kingdom; the Department of Circulation (M.Y.), Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan; Institute of Membrane and Systems Biology (G.M.G.), University of Leeds, Leeds, United Kingdom; and Centre for Integrated Systems Biology (R.B.), University of Nottingham, Nottingham, United Kingdom
| | - Rudi Billeter
- From the Cardiovascular Research Group (I.D.G., J.O.T., H.D., M.R.B.), Faculty of Medical and Human Sciences, University of Manchester, Core Technology Facility, Manchester, United Kingdom; the Department of Circulation (M.Y.), Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan; Institute of Membrane and Systems Biology (G.M.G.), University of Leeds, Leeds, United Kingdom; and Centre for Integrated Systems Biology (R.B.), University of Nottingham, Nottingham, United Kingdom
| | - Mark R. Boyett
- From the Cardiovascular Research Group (I.D.G., J.O.T., H.D., M.R.B.), Faculty of Medical and Human Sciences, University of Manchester, Core Technology Facility, Manchester, United Kingdom; the Department of Circulation (M.Y.), Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan; Institute of Membrane and Systems Biology (G.M.G.), University of Leeds, Leeds, United Kingdom; and Centre for Integrated Systems Biology (R.B.), University of Nottingham, Nottingham, United Kingdom
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Aslanidi OV, Dewey RS, Morgan AR, Boyett MR, Zhang H. Regional differences in rabbit atrial action potential properties: mechanisms, consequences and pharmacological implications. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2009; 2008:141-4. [PMID: 19162613 DOI: 10.1109/iembs.2008.4649110] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Regional differences in electrical action potential (AP) properties can provide a substrate for atrial arrhythmias. We quantify such differences by developing detailed AP models for the left (LA) and right (RA) rabbit atrial cells in order to study the underlying electrophysiological mechanisms, as well as their impacts on vulnerable properties of the atrial tissue. The transient outward current, Ito, is identified as the major factor contributing to the AP differences between the LA and RA cells, which suggests a potential pharmacological target for reducing heterogeneity and vulnerability of the atria.
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Affiliation(s)
- Oleg V Aslanidi
- School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, United Kingdom.
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Affiliation(s)
- Halina Dobrzynski
- Cardiovascular Research Group, School of Medicine, University of Manchester, Core Technology Facility, 46 Grafton St, Manchester M13 9NT, UK
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Tellez JO, Dobrzynski H, Greener ID, Graham GM, Laing E, Honjo H, Hubbard SJ, Boyett MR, Billeter R. Differential expression of ion channel transcripts in atrial muscle and sinoatrial node in rabbit. Circ Res 2006; 99:1384-93. [PMID: 17082478 DOI: 10.1161/01.res.0000251717.98379.69] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The aim of the study was to identify ion channel transcripts expressed in the sinoatrial node (SAN), the pacemaker of the heart. Functionally, the SAN can be divided into central and peripheral regions (center is adapted for pacemaking only, whereas periphery is adapted to protect center and drive atrial muscle as well as pacemaking) and the aim was to study expression in both regions. In rabbit tissue, the abundance of 30 transcripts (including transcripts for connexin, Na(+), Ca(2+), hyperpolarization-activated cation and K(+) channels, and related Ca(2+) handling proteins) was measured using quantitative PCR and the distribution of selected transcripts was visualized using in situ hybridization. Quantification of individual transcripts (quantitative PCR) showed that there are significant differences in the abundance of 63% of the transcripts studied between the SAN and atrial muscle, and cluster analysis showed that the transcript profile of the SAN is significantly different from that of atrial muscle. There are apparent isoform switches on moving from atrial muscle to the SAN center: RYR2 to RYR3, Na(v)1.5 to Na(v)1.1, Ca(v)1.2 to Ca(v)1.3 and K(v)1.4 to K(v)4.2. The transcript profile of the SAN periphery is intermediate between that of the SAN center and atrial muscle. For example, Na(v)1.5 messenger RNA is expressed in the SAN periphery (as it is in atrial muscle), but not in the SAN center, and this is probably related to the need of the SAN periphery to drive the surrounding atrial muscle.
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Wang TM, Chiang CE, Sheu JR, Tsou CH, Chang HM, Luk HN. Homogenous distribution of fast response action potentials in canine pulmonary vein sleeves: a contradictory report. Int J Cardiol 2003; 89:187-95. [PMID: 12767542 DOI: 10.1016/s0167-5273(02)00474-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Pulmonary veins may serve as source of ectopic focus (or foci) in initiating atrial tachyarrhythmias in human beings. However, the animal model for such focal atrial fibrillation is still lacking and cellular mechanism for arrhythmias remains to be studied. Recently, a series of reports of cellular electrophysiological characterization of pulmonary vein sleeves demonstrated an extremely high incidence of automaticity (varied from 40 to 76%) and triggered activity (from 0 to 44%) in normal healthy control dogs and rabbits. The present study was therefore designed to re-investigate the cellular electrophysiological properties of canine pulmonary veins. Intracellular action potentials were characterized in pulmonary vein sleeves in 50 normal healthy dogs. Conventional glass microelectrode recording technique was used. Experiments were focused on the incidence of automaticity and triggered activity in pulmonary vein sleeve tissues. Surprisingly, our results showed that all pulmonary vein sleeves tissues in these dogs displayed fast-response action potentials under the well-controlled experimental condition (100%, n=50). No spontaneous pacemaking activities, early or delayed afterdepolarisations were observed (0%, n=50). No high-frequency spikes or irregular rhythm could be recorded in all experiments (0%, n=50). Both the frequency response and membrane responsiveness of the pulmonary vein action potentials were characterized. No electrophysiological inhomogeneity between the distal and the proximal part of the sleeves was observed. In conclusion, canine pulmonary vein sleeves do not display arrhythmogenic activities under normal physiological conditions. The possible explanations for the controversy in pulmonary veins electrophysiology were discussed.
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Affiliation(s)
- Tsui-min Wang
- Graduate Institute of Medical Science, Taipei Medical University, Taipei, Taiwan
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Kurata Y, Hisatome I, Imanishi S, Shibamoto T. Dynamical description of sinoatrial node pacemaking: improved mathematical model for primary pacemaker cell. Am J Physiol Heart Circ Physiol 2002; 283:H2074-101. [PMID: 12384487 DOI: 10.1152/ajpheart.00900.2001] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We developed an improved mathematical model for a single primary pacemaker cell of the rabbit sinoatrial node. Original features of our model include 1) incorporation of the sustained inward current (I(st)) recently identified in primary pacemaker cells, 2) reformulation of voltage- and Ca(2+)-dependent inactivation of the L-type Ca(2+) channel current (I(Ca,L)), 3) new expressions for activation kinetics of the rapidly activating delayed rectifier K(+) channel current (I(Kr)), and 4) incorporation of the subsarcolemmal space as a diffusion barrier for Ca(2+). We compared the simulated dynamics of our model with those of previous models, as well as with experimental data, and examined whether the models could accurately simulate the effects of modulating sarcolemmal ionic currents or intracellular Ca(2+) dynamics on pacemaker activity. Our model represents significant improvements over the previous models, because it can 1) simulate whole cell voltage-clamp data for I(Ca,L), I(Kr), and I(st); 2) reproduce the waveshapes of spontaneous action potentials and ionic currents during action potential clamp recordings; and 3) mimic the effects of channel blockers or Ca(2+) buffers on pacemaker activity more accurately than the previous models.
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Affiliation(s)
- Yasutaka Kurata
- Department of Physiology, Kanazawa Medical University, 1-1 Daigaku, Uchinada-machi, Kahoku-gun, Ishikawa 920-0293, Japan.
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Balla Z, Hoch B, Karczewski P, Blasig IE. Calcium/calmodulin-dependent protein kinase IIdelta 2 and gamma isoforms regulate potassium currents of rat brain capillary endothelial cells under hypoxic conditions. J Biol Chem 2002; 277:21306-14. [PMID: 11925434 DOI: 10.1074/jbc.m200553200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Endothelial K+ and Ca2+ homeostasis plays an important role in the regulation of tissue supply and metabolism under normal and pathological conditions. However, the exact molecular mechanism of how Ca2+ is involved in the regulation of K+ homeostasis in capillary endothelial cells, especially under oxidative stress, is not clear. To reveal Ca2+-triggered pathways, which modulate K+ homeostasis, Ca2+/calmodulin-dependent protein kinase II and voltage-gated outward K+ currents were studied in rat brain capillary endothelial cells under hypoxia. Whole cell voltage-clamp measurements showed voltage-gated outward K+ current with transient and sustained components. mRNA and protein of Ca2+/calmodulin-dependent protein kinase II delta2 and two gamma isoenzymes were identified. Activation of the isoforms (autophosphorylation) was typically achieved by the Ca2+ ionophore ionomycin, which was prevented by the Ca2+/calmodulin-dependent protein kinase II-specific inhibitor KN-93. Hypoxia resulted in autophosphorylation of the delta2 and gammaB isoforms, augmented the current amplitude, increased the inactivation time constant, and decreased the extent of inactivation of the transient current. KN-93 prevented both the activation of the isoforms and the alterations in the K+ current characteristics. It is concluded that the activation of Ca2+/calmodulin-dependent protein kinase II decreases inactivation of the voltage-gated outward K+ current, thereby counteracting depolarization of the hypoxic endothelium.
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Affiliation(s)
- Zsolt Balla
- Forschungsinstitut für Molekulare Pharmakologie, Berlin, 13125 Germany
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Oudit GY, Kassiri Z, Sah R, Ramirez RJ, Zobel C, Backx PH. The molecular physiology of the cardiac transient outward potassium current (I(to)) in normal and diseased myocardium. J Mol Cell Cardiol 2001; 33:851-72. [PMID: 11343410 DOI: 10.1006/jmcc.2001.1376] [Citation(s) in RCA: 131] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
G. Y. Oudit, Z. Kassiri, R. Sah, R. J. Ramirez, C. Zobel and P. H. Backx. The Molecular Physiology of the Cardiac Transient Outward Potassium Current (I(to)) in Normal and Diseased Myocardium. Journal of Molecular and Cellular Cardiology (2001) 33, 851-872. The Ca(2+)-independent transient outward potassium current (I(to)) plays an important role in early repolarization of the cardiac action potential. I(to)has been clearly demonstrated in myocytes from different cardiac regions and species. Two kinetic variants of cardiac I(to)have been identified: fast I(to), called I(to,f), and slow I(to), called I(to,s). Recent findings suggest that I(to,f)is formed by assembly of K(v4.2)and/or K(v4.3)alpha pore-forming voltage-gated subunits while I(to,s)is comprised of K(v1.4)and possibly K(v1.7)subunits. In addition, several regulatory subunits and pathways modulating the level and biophysical properties of cardiac I(to)have been identified. Experimental findings and data from computer modeling of cardiac action potentials have conclusively established an important physiological role of I(to)in rodents, with its role in large mammals being less well defined due to complex interplay between a multitude of cardiac ionic currents. A central and consistent electrophysiological change in cardiac disease is the reduction in I(to)density with a loss of heterogeneity of I(to)expression and associated action potential prolongation. Alterations of I(to)in rodent cardiac disease have been linked to repolarization abnormalities and alterations in intracellular Ca(2+)homeostasis, while in larger mammals the link with functional changes is far less certain. We review the current literature on the molecular basis for cardiac I(to)and the functional consequences of changes in I(to)that occur in cardiovascular disease.
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Affiliation(s)
- G Y Oudit
- Department of Medicine and Physiology, Toronto General Hospital, 101 College Street, Toronto, M5G 2C4, Canada
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