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Huang X, Choi S, Wu W, Shahi PK, Lee JH, Hong C, Jun JY. 5-Hydroxytryptamine Enhances the Pacemaker Activity of Interstitial Cells of Cajal in Mouse Colon. Int J Mol Sci 2024; 25:3997. [PMID: 38612808 PMCID: PMC11012597 DOI: 10.3390/ijms25073997] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2024] [Revised: 04/02/2024] [Accepted: 04/02/2024] [Indexed: 04/14/2024] Open
Abstract
We examined the localization of the 5-hydroxytryptamine (5-HT) receptor and its effects on mouse colonic interstitial cells of Cajal (ICCs) using electrophysiological techniques. Treatment with 5-HT increased the pacemaker activity in colonic ICCs with depolarization of membrane potentials in a dose-dependent manner. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channel blockers blocked pacemaker activity and 5-HT-induced effects. Moreover, an adenylate cyclase inhibitor inhibited 5-HT-induced effects, and cell-permeable 8-bromo-cAMP increased the pacemaker activity. Various agonists of the 5-HT receptor subtype were working in colonic ICCs, including the 5-HT4 receptor. In small intestinal ICCs, 5-HT depolarized the membrane potentials transiently. Adenylate cyclase inhibitors or HCN blockers did not show any influence on 5-HT-induced effects. Anoctamin-1 (ANO1) or T-type Ca2+ channel blockers inhibited the pacemaker activity of colonic ICCs and blocked 5-HT-induced effects. A tyrosine protein kinase inhibitor inhibited pacemaker activity in colonic ICCs under controlled conditions but did not show any influence on 5-HT-induced effects. Among mitogen-activated protein kinase (MAPK) inhibitors, a p38 MAPK inhibitor inhibited 5-HT-induced effects on colonic ICCs. Thus, 5-HT's effect on pacemaker activity in small intestinal and colonic ICCs has excitatory but variable patterns. ANO1, T-type Ca2+, and HCN channels are involved in 5-HT-induced effects, and MAPKs are involved in 5-HT effects in colonic ICCs.
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Affiliation(s)
- Xingyou Huang
- Department of Physiology, College of Medicine, Chosun University, Gwangju 61452, Republic of Korea; (X.H.); (S.C.); (W.W.); (P.K.S.); (C.H.)
| | - Seok Choi
- Department of Physiology, College of Medicine, Chosun University, Gwangju 61452, Republic of Korea; (X.H.); (S.C.); (W.W.); (P.K.S.); (C.H.)
| | - Wenhao Wu
- Department of Physiology, College of Medicine, Chosun University, Gwangju 61452, Republic of Korea; (X.H.); (S.C.); (W.W.); (P.K.S.); (C.H.)
| | - Pawan Kumar Shahi
- Department of Physiology, College of Medicine, Chosun University, Gwangju 61452, Republic of Korea; (X.H.); (S.C.); (W.W.); (P.K.S.); (C.H.)
| | - Jun Hyung Lee
- Department of Internal Medicine, College of Medicine, Chosun University, Gwangju 61452, Republic of Korea;
| | - Chansik Hong
- Department of Physiology, College of Medicine, Chosun University, Gwangju 61452, Republic of Korea; (X.H.); (S.C.); (W.W.); (P.K.S.); (C.H.)
| | - Jae Yeoul Jun
- Department of Physiology, College of Medicine, Chosun University, Gwangju 61452, Republic of Korea; (X.H.); (S.C.); (W.W.); (P.K.S.); (C.H.)
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Shim JV, Xiong Y, Dhanan P, Dariolli R, Azeloglu EU, Hu B, Jayaraman G, Schaniel C, Birtwistle MR, Iyengar R, Dubois NC, Sobie EA. Predicting individual-specific cardiotoxicity responses induced by tyrosine kinase inhibitors. Front Pharmacol 2023; 14:1158222. [PMID: 37101545 PMCID: PMC10123273 DOI: 10.3389/fphar.2023.1158222] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Accepted: 03/27/2023] [Indexed: 04/28/2023] Open
Abstract
Introduction: Tyrosine kinase inhibitor drugs (TKIs) are highly effective cancer drugs, yet many TKIs are associated with various forms of cardiotoxicity. The mechanisms underlying these drug-induced adverse events remain poorly understood. We studied mechanisms of TKI-induced cardiotoxicity by integrating several complementary approaches, including comprehensive transcriptomics, mechanistic mathematical modeling, and physiological assays in cultured human cardiac myocytes. Methods: Induced pluripotent stem cells (iPSCs) from two healthy donors were differentiated into cardiac myocytes (iPSC-CMs), and cells were treated with a panel of 26 FDA-approved TKIs. Drug-induced changes in gene expression were quantified using mRNA-seq, changes in gene expression were integrated into a mechanistic mathematical model of electrophysiology and contraction, and simulation results were used to predict physiological outcomes. Results: Experimental recordings of action potentials, intracellular calcium, and contraction in iPSC-CMs demonstrated that modeling predictions were accurate, with 81% of modeling predictions across the two cell lines confirmed experimentally. Surprisingly, simulations of how TKI-treated iPSC-CMs would respond to an additional arrhythmogenic insult, namely, hypokalemia, predicted dramatic differences between cell lines in how drugs affected arrhythmia susceptibility, and these predictions were confirmed experimentally. Computational analysis revealed that differences between cell lines in the upregulation or downregulation of particular ion channels could explain how TKI-treated cells responded differently to hypokalemia. Discussion: Overall, the study identifies transcriptional mechanisms underlying cardiotoxicity caused by TKIs, and illustrates a novel approach for integrating transcriptomics with mechanistic mathematical models to generate experimentally testable, individual-specific predictions of adverse event risk.
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Affiliation(s)
- Jaehee V. Shim
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
- Institute for Systems Biomedicine, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Yuguang Xiong
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
- Institute for Systems Biomedicine, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Priyanka Dhanan
- Department of Cell, Developmental and Regenerative Biology, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Rafael Dariolli
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
- Institute for Systems Biomedicine, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Evren U. Azeloglu
- Institute for Systems Biomedicine, Icahn School of Medicine at Mount Sinai, New York, NY, United States
- Division of Nephrology, Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Bin Hu
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
- Institute for Systems Biomedicine, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Gomathi Jayaraman
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
- Institute for Systems Biomedicine, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Christoph Schaniel
- Institute for Systems Biomedicine, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | | | - Ravi Iyengar
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
- Institute for Systems Biomedicine, Icahn School of Medicine at Mount Sinai, New York, NY, United States
- *Correspondence: Ravi Iyengar, ; Eric A. Sobie,
| | - Nicole C. Dubois
- Department of Cell, Developmental and Regenerative Biology, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Eric A. Sobie
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
- Institute for Systems Biomedicine, Icahn School of Medicine at Mount Sinai, New York, NY, United States
- *Correspondence: Ravi Iyengar, ; Eric A. Sobie,
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3
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Peters CH, Singh RK, Bankston JR, Proenza C. Regulation of HCN Channels by Protein Interactions. Front Physiol 2022; 13:928507. [PMID: 35795651 PMCID: PMC9251338 DOI: 10.3389/fphys.2022.928507] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Accepted: 06/01/2022] [Indexed: 11/30/2022] Open
Abstract
Hyperpolarization-activated, cyclic nucleotide-sensitive (HCN) channels are key regulators of subthreshold membrane potentials in excitable cells. The four mammalian HCN channel isoforms, HCN1-HCN4, are expressed throughout the body, where they contribute to diverse physiological processes including cardiac pacemaking, sleep-wakefulness cycles, memory, and somatic sensation. While all HCN channel isoforms produce currents when expressed by themselves, an emerging list of interacting proteins shape HCN channel excitability to influence the physiologically relevant output. The best studied of these regulatory proteins is the auxiliary subunit, TRIP8b, which binds to multiple sites in the C-terminus of the HCN channels to regulate expression and disrupt cAMP binding to fine-tune neuronal HCN channel excitability. Less is known about the mechanisms of action of other HCN channel interaction partners like filamin A, Src tyrosine kinase, and MinK-related peptides, which have a range of effects on HCN channel gating and expression. More recently, the inositol trisphosphate receptor-associated cGMP-kinase substrates IRAG1 and LRMP (also known as IRAG2), were discovered as specific regulators of the HCN4 isoform. This review summarizes the known protein interaction partners of HCN channels and their mechanisms of action and identifies gaps in our knowledge.
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Affiliation(s)
- Colin H. Peters
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Rohit K. Singh
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - John R. Bankston
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Catherine Proenza
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
- Department of Cardiology, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
- *Correspondence: Catherine Proenza,
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Lu Z, Wang HZ, Gordon CR, Ballou LM, Lin RZ, Cohen IS. Regulation of HCN2 Current by PI3K/Akt Signaling. Front Physiol 2020; 11:587040. [PMID: 33240105 PMCID: PMC7680966 DOI: 10.3389/fphys.2020.587040] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 10/16/2020] [Indexed: 12/19/2022] Open
Abstract
It has long been known that heart rate is regulated by the autonomic nervous system. Recently, we demonstrated that the pacemaker current, If, is regulated by phosphoinositide 3-kinase (PI3K) signaling independently of the autonomic nervous system. Inhibition of PI3K in sinus node (SN) myocytes shifts the activation of If by almost 16 mV in the negative direction. If in the SN is predominantly mediated by two members of the HCN gene family, HCN4 and HCN1. Purkinje fibers also possess If and are an important secondary pacemaker in the heart. In contrast to the SN, they express HCN2 and HCN4, while ventricular myocytes, which do not normally pace, express HCN2 alone. In the current work, we investigated PI3K regulation of HCN2 expressed in HEK293 cells. Treatment with the PI3K inhibitor PI-103 caused a negative shift in the activation voltage and a dramatic reduction in the magnitude of the HCN2 current. Similar changes were also seen in cells treated with an inhibitor of the protein kinase Akt, a downstream effector of PI3K. The effects of PI-103 were reversed by perfusion of cells with phosphatidylinositol 3,4,5-trisphosphate (the second messenger produced by PI3K) or active Akt protein. We identified serine 861 in mouse HCN2 as a putative Akt phosphorylation site. Mutation of S861 to alanine mimicked the effects of Akt inhibition on voltage dependence and current magnitude. In addition, the Akt inhibitor had no effect on the mutant channel. These results suggest that Akt phosphorylation of mHCN2 S861 accounts for virtually all of the observed actions of PI3K signaling on the HCN2 current. Unexpectedly, Akt inhibition had no effect on If in SN myocytes. This result raises the possibility that diverse PI3K signaling pathways differentially regulate HCN-induced currents in different tissues, depending on the isoforms expressed.
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Affiliation(s)
- Zhongju Lu
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, United States.,Department of Medicine, Stony Brook University, Stony Brook, NY, United States
| | - Hong Zhan Wang
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, United States
| | - Chris R Gordon
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, United States.,Department of Nephrology, Stony Brook University, Stony Brook, NY, United States
| | - Lisa M Ballou
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, United States
| | - Richard Z Lin
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, United States.,Medical Service, Northport VA Medical Center, Northport, NY, United States
| | - Ira S Cohen
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, United States
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DiFrancesco D. Comparing pathways for long-term heart rate modulation by the funny current. J Gen Physiol 2019; 151:1066-1069. [PMID: 31431492 PMCID: PMC6719408 DOI: 10.1085/jgp.201912409] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Heart rate control by the funny current (If) involves both fast, cAMP-dependent, and slow, membrane expression–based mechanisms to adapt to different needs.
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Affiliation(s)
- Dario DiFrancesco
- Department of Biosciences, University of Milano and Istituto di Biofisica-Consiglio Nazionale delle Ricerche, Milano, Italy
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Sartiani L, Mannaioni G, Masi A, Novella Romanelli M, Cerbai E. The Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels: from Biophysics to Pharmacology of a Unique Family of Ion Channels. Pharmacol Rev 2017; 69:354-395. [PMID: 28878030 DOI: 10.1124/pr.117.014035] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Accepted: 07/07/2017] [Indexed: 12/22/2022] Open
Abstract
Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels are important members of the voltage-gated pore loop channels family. They show unique features: they open at hyperpolarizing potential, carry a mixed Na/K current, and are regulated by cyclic nucleotides. Four different isoforms have been cloned (HCN1-4) that can assemble to form homo- or heterotetramers, characterized by different biophysical properties. These proteins are widely distributed throughout the body and involved in different physiologic processes, the most important being the generation of spontaneous electrical activity in the heart and the regulation of synaptic transmission in the brain. Their role in heart rate, neuronal pacemaking, dendritic integration, learning and memory, and visual and pain perceptions has been extensively studied; these channels have been found also in some peripheral tissues, where their functions still need to be fully elucidated. Genetic defects and altered expression of HCN channels are linked to several pathologies, which makes these proteins attractive targets for translational research; at the moment only one drug (ivabradine), which specifically blocks the hyperpolarization-activated current, is clinically available. This review discusses current knowledge about HCN channels, starting from their biophysical properties, origin, and developmental features, to (patho)physiologic role in different tissues and pharmacological modulation, ending with their present and future relevance as drug targets.
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Affiliation(s)
- Laura Sartiani
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Guido Mannaioni
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Alessio Masi
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Maria Novella Romanelli
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Elisabetta Cerbai
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
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7
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Baruscotti M, Bianco E, Bucchi A, DiFrancesco D. Current understanding of the pathophysiological mechanisms responsible for inappropriate sinus tachycardia: role of the If "funny" current. J Interv Card Electrophysiol 2016; 46:19-28. [PMID: 26781742 DOI: 10.1007/s10840-015-0097-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 12/28/2015] [Indexed: 01/01/2023]
Abstract
BACKGROUND Together with the afferent branches of the autonomic nervous system, the sinoatrial node (SAN) forms a functional unit whose function is to fire rhythmic action potentials at a rate optimal for coping with the metabolic needs of the body. Dysfunctional behavior of this complex unit may thus result in SAN rhythm disorders. Among these disorders, there is the inappropriate sinus tachycardia (IST) which occurs when an unjustified fast SAN rate is present. METHODS We here present a critical review of the role of pacemaker f/HCN channels in cardiac rhythm generation and modulation and their involvement in IST. RESULTS Recent evidence demonstrates that a familial form of IST is associated with a gain-of-function mutation in the HCN4 pacemaker channel (R524Q) which confers an increased sensitivity to the second messenger cAMP, a key mediator in sympathetic modulation. CONCLUSIONS This finding is consistent with the general view that hypersympathetic tone is one of the causes of IST and introduces the novel concept of defective funny channel-dependent tachyarrhythmias.
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Affiliation(s)
- Mirko Baruscotti
- Department of Biosciences, Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata, University of Milano, via Celoria 26, 20133, Milano, Italy.
| | - Elisabetta Bianco
- Cardiovascular Department, "Ospedali Riuniti di Trieste", University Hospital, Trieste, Italy
| | - Annalisa Bucchi
- Department of Biosciences, Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata, University of Milano, via Celoria 26, 20133, Milano, Italy
| | - Dario DiFrancesco
- Department of Biosciences, Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata, University of Milano, via Celoria 26, 20133, Milano, Italy.
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He C, Chen F, Li B, Hu Z. Neurophysiology of HCN channels: From cellular functions to multiple regulations. Prog Neurobiol 2014; 112:1-23. [DOI: 10.1016/j.pneurobio.2013.10.001] [Citation(s) in RCA: 230] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2012] [Revised: 10/01/2013] [Accepted: 10/07/2013] [Indexed: 12/18/2022]
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Lewis AS, Estep CM, Chetkovich DM. The fast and slow ups and downs of HCN channel regulation. Channels (Austin) 2011; 4:215-31. [PMID: 20305382 DOI: 10.4161/chan.4.3.11630] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels (h channels) form the molecular basis for the hyperpolarization-activated current, I(h), and modulation of h channels contributes to changes in cellular properties critical for normal functions in the mammalian brain and heart. Numerous mechanisms underlie h channel modulation during both physiological and pathological conditions, leading to distinct changes in gating, kinetics, surface expression, channel conductance or subunit composition of h channels. Here we provide a focused review examining mechanisms of h channel regulation, with an emphasis on recent findings regarding interacting proteins such as TRIP8b. This review is intended to serve as a comprehensive resource for physiologists to provide potential molecular mechanisms underlying functionally important changes in I(h) in different biological models, as well as for molecular biologists to delineate the predicted h channel changes associated with complex regulatory mechanisms in both normal function and in disease states.
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Affiliation(s)
- Alan S Lewis
- Davee Department of Neurology and Clinical Neurosciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
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Biel M, Wahl-Schott C, Michalakis S, Zong X. Hyperpolarization-activated cation channels: from genes to function. Physiol Rev 2009; 89:847-85. [PMID: 19584315 DOI: 10.1152/physrev.00029.2008] [Citation(s) in RCA: 726] [Impact Index Per Article: 48.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels comprise a small subfamily of proteins within the superfamily of pore-loop cation channels. In mammals, the HCN channel family comprises four members (HCN1-4) that are expressed in heart and nervous system. The current produced by HCN channels has been known as I(h) (or I(f) or I(q)). I(h) has also been designated as pacemaker current, because it plays a key role in controlling rhythmic activity of cardiac pacemaker cells and spontaneously firing neurons. Extensive studies over the last decade have provided convincing evidence that I(h) is also involved in a number of basic physiological processes that are not directly associated with rhythmicity. Examples for these non-pacemaking functions of I(h) are the determination of the resting membrane potential, dendritic integration, synaptic transmission, and learning. In this review we summarize recent insights into the structure, function, and cellular regulation of HCN channels. We also discuss in detail the different aspects of HCN channel physiology in the heart and nervous system. To this end, evidence on the role of individual HCN channel types arising from the analysis of HCN knockout mouse models is discussed. Finally, we provide an overview of the impact of HCN channels on the pathogenesis of several diseases and discuss recent attempts to establish HCN channels as drug targets.
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Affiliation(s)
- Martin Biel
- Center for Integrated Protein Science CIPS-M and Zentrum für Pharmaforschung, Department Pharmazie, Pharmakologie für Naturwissenschaften, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, Munich D-81377, Germany.
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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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12
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Rozario AO, Turbendian HK, Fogle KJ, Olivier NB, Tibbs GR. Voltage-dependent opening of HCN channels: Facilitation or inhibition by the phytoestrogen, genistein, is determined by the activation status of the cyclic nucleotide gating ring. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:1939-49. [PMID: 19524546 DOI: 10.1016/j.bbamem.2009.06.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2009] [Revised: 05/29/2009] [Accepted: 06/08/2009] [Indexed: 11/27/2022]
Abstract
Investigation of the mechanistic bases and physiological importance of cAMP regulation of HCN channels has exploited an arginine to glutamate mutation in the nucleotide-binding fold, an approach critically dependent on the mutation selectively lowering the channel's nucleotide affinity. In apparent conflict with this, in intact Xenopus oocytes, HCN and HCN-RE channels exhibit qualitatively and quantitatively distinct responses to the tyrosine kinase inhibitor, genistein -- the estrogenic isoflavonoid strongly depolarizes the activation mid-point of HCN1-R538E, but not HCN1 channels (+9.8 mV + or - 0.9 versus +2.2 mV + or - 0.6) and hyperpolarizes gating of HCN2 (-4.8 mV + or - 1.0) but depolarizes gating of HCN2-R591E (+13.2 mV + or - 2.1). However, excised patch recording, X-ray crystallography and modeling reveal that this is not due to either a fundamental effect of the mutation on channel gating per se or of genistein acting as a mutation-sensitive partial agonist at the cAMP site. Rather, we find that genistein equivalently moves both HCN and HCN-RE channels closer to the open state (rendering the channels inherently easier to open but at a cost of decreasing the coupling energy of cAMP) and that the anomaly reflects a balance of these energetic effects with the isoform-specific inhibition of activation by the nucleotide gating ring and relief of this by endogenous cAMP. These findings have specific implications with regard to findings based on HCN-RE channels and kinase antagonists and general implications with respect to interpretation of drug effects in mutant channel backgrounds.
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Affiliation(s)
- Anjali O Rozario
- Department of Anesthesiology, Columbia University, New York, NY 10032, USA
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Kryukova Y, Rybin VO, Qu J, Steinberg SF, Robinson RB. Age-dependent differences in the inhibition of HCN2 current in rat ventricular myocytes by the tyrosine kinase inhibitor erbstatin. Pflugers Arch 2008; 457:821-30. [PMID: 18696104 DOI: 10.1007/s00424-008-0565-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Revised: 06/27/2008] [Accepted: 07/26/2008] [Indexed: 10/21/2022]
Abstract
Previously, we have shown that murine HCN2 channels over-expressed in newborn and adult cardiac myocytes produce currents with different biophysical characteristics. To investigate the role of tyrosine kinase modulation in these age-dependent differences, we employed the broad spectrum tyrosine kinase inhibitor erbstatin. Our results demonstrated distinct and separable effects of erbstatin on channel gating and current amplitude and a marked age dependence to these effects. In newborn myocytes, erbstatin decreased current amplitude, shifted the activation relation negative, and slowed activation kinetics. The effect on activation voltage but not that on amplitude was absent when expressing a cAMP-insensitive mutant (HCN2R/E), while a C-terminal truncated form of HCN2 (HCN2DeltaCx) exhibited only the voltage dependent but not the amplitude effect of erbstatin. Thus, the action of erbstatin on the activation relation and current amplitude are distinct and separable in newborn myocytes, and the effect on activation voltage depends on the cAMP status of HCN2 channels. In contrast to newborn myocytes, erbstatin had no effect on HCN2 under control conditions in adult myocytes but induced a negative shift with no change in amplitude when saturated cAMP was added to the pipette solution. We conclude that erbstatin's effects on HCN2 current magnitude and voltage dependence are distinct and separable, and there are fundamental developmental differences in the heart that affect channel function and its modulation by the tyrosine kinase inhibitor erbstatin.
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Affiliation(s)
- Yelena Kryukova
- Department of Pharmacology, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032, USA
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Pian P, Bucchi A, Decostanzo A, Robinson RB, Siegelbaum SA. Modulation of cyclic nucleotide-regulated HCN channels by PIP(2) and receptors coupled to phospholipase C. Pflugers Arch 2007; 455:125-45. [PMID: 17605039 DOI: 10.1007/s00424-007-0295-2] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2007] [Accepted: 05/16/2007] [Indexed: 10/24/2022]
Abstract
Recent results indicate that phosphoinositides, including phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)), directly enhance the opening of hyperpolarization-activated, cyclic nucleotide-regulated (HCN) channels by shifting their activation gating to more positive voltages. This contrasts with the action of phosphoinositides to inhibit the opening of the related cyclic nucleotide-gated (CNG) channels involved in sensory signaling. We both review previous studies and present new experiments that investigate whether HCN channels may be regulated by dynamic changes in PI(4,5)P(2) levels caused by the receptor-mediated activation of phospholipase C (PLC). We coexpressed HCN1 or HCN2 channels in Xenopus oocytes with the PLC-coupled bradykinin BK(2) receptor, the muscarinic M1 receptor, or the TrkA receptor. Activation of all three receptors produced a positive shift in HCN channel voltage gating, the opposite of the effect expected for PI(4,5)P(2) depletion. This action was not caused by alterations in cAMP as the effect was preserved in HCN mutant channels that fail to bind cAMP. The receptor effects were mediated by PLC activity, but did not depend on signaling through the downstream products of PI(4,5)P(2) hydrolysis: IP(3) or diacylglycerol (DAG). Importantly, the modulatory effects on gating were blocked by inhibitors of phosphatidylinositol (PI) kinases, suggesting a role for increased PI(4,5)P(2) synthesis. Finally, we found that bradykinin exerted a similar PI kinase-dependent effect on the gating of native HCN channels in cardiac sinoatrial node cells, suggesting that this pathway may represent a novel, physiologically relevant mechanism for enhancing HCN channel function.
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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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15
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Missan S, Zhabyeyev P, Linsdell P, McDonald TF. Insensitivity of cardiac delayed-rectifier I(Kr) to tyrosine phosphorylation inhibitors and stimulators. Br J Pharmacol 2006; 148:724-31. [PMID: 16715119 PMCID: PMC1751861 DOI: 10.1038/sj.bjp.0706776] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1. The rapidly activating delayed-rectifying K+ current (I(Kr)) in heart cells is an important determinant of repolarisation, and decreases in its density are implicated in acquired and inherited long QT syndromes. The objective of the present study on I(Kr) in guinea-pig ventricular myocytes was to evaluate whether the current is acutely regulated by tyrosine phosphorylation. 2. Myocytes configured for ruptured-patch or perforated-patch voltage-clamp were depolarised with 200-ms steps to 0 mV for measurement of I(Kr) tail amplitude on repolarisations to -40 mV. 3. I(Kr) in both ruptured-patch and perforated-patch myocytes was only moderately (14-20%) decreased by 100 microM concentrations of protein tyrosine kinase (PTK) inhibitors tyrphostin A23, tyrphostin A25, and genistein. However, similar-sized decreases were induced by PTK-inactive analogues tyrphostin A1 and daidzein, suggesting that they were unrelated to inhibition of PTK. 4. Ruptured-patch and perforated-patch myocytes were also treated with promoters of tyrosine phosphorylation, including phosphotyrosyl phosphatase (PTP) inhibitor orthovanadate, exogenous c-Src PTK, and four receptor PTK activators (insulin, insulin-like growth factor-1, epidermal growth factor, and basic fibroblast growth factor). None of these treatments had a significant effect on the amplitude of I(Kr). 5. We conclude that Kr channels in guinea-pig ventricular myocytes are unlikely to be regulated by PTK and PTP.
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Affiliation(s)
- Sergey Missan
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7
| | - Pavel Zhabyeyev
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7
| | - Paul Linsdell
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7
| | - Terence F McDonald
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7
- Author for correspondence:
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16
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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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17
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Missan S, Linsdell P, McDonald TF. Tyrosine kinase and phosphatase regulation of slow delayed-rectifier K+ current in guinea-pig ventricular myocytes. J Physiol 2006; 573:469-82. [PMID: 16581870 PMCID: PMC1779722 DOI: 10.1113/jphysiol.2005.104422] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The objective of this study was to investigate the involvement of tyrosine phosphorylation in the regulation of the cardiac slowly activating delayed-rectifier K(+) current (I(Ks)) that is important for action potential repolarization. Constitutive I(Ks) recorded from guinea-pig ventricular myocytes was suppressed by broad-spectrum tyrosine kinase (TK) inhibitors tyrphostin A23 (IC(50), 4.1+/-0.6 microm), tyrphostin A25 (IC(50), 12.1+/-2.1 microm) and genistein (IC(50), 64+/-4 microm), but was relatively insensitive to the inactive analogues tyrphostin A1, tyrphostin A63, daidzein and genistin. I(Ks) was unaffected by AG1478 (10 microm), an inhibitor of epidermal growth factor receptor TK, and was strongly suppressed by the Src TK inhibitor PP2 (10 microm) but not by the inactive analogue PP3 (10 microm). The results of experiments with forskolin, H89 and bisindolylmaleimide I indicate that the suppression of I(Ks) by TK inhibitors was not mediated via inhibition of (I(Ks)-stimulatory) protein kinases A and C. To evaluate whether the suppression was related to lowered tyrosine phosphorylation, myocytes were pretreated with TK inhibitors and then exposed to the phosphotyrosyl phosphatase inhibitor orthovanadate (1 mm). Orthovanadate almost completely reversed the suppression of I(Ks) induced by broad-spectrum TK inhibitors at concentrations around their IC(50) values. We conclude that basal I(Ks) is strongly dependent on tyrosine phosphorylation of Ks channel (or channel-regulatory) protein.
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Affiliation(s)
- Sergey Missan
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7
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18
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Cohen IS, Robinson RB. Pacemaker current and automatic rhythms: toward a molecular understanding. Handb Exp Pharmacol 2006:41-71. [PMID: 16610340 DOI: 10.1007/3-540-29715-4_2] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The ionic basis of automaticity in the sinoatrial node and His-Purkinje system, the primary and secondary cardiac pacemaking regions, is discussed. Consideration is given to potential targets for pharmacologic or genetic therapies of rhythm disorders. An ideal target would be an ion channel that functions only during diastole, so that action potential repolarization is not affected, and one that exhibits regional differences in expression and/or function so that the primary and secondary pacemakers can be selectively targeted. The so-called pacemaker current, If, generated by the HCN gene family, best fits these criteria. The biophysical and molecular characteristics of this current are reviewed, and progress to date in developing selective pharmacologic agents targeting If and in using gene and cell-based therapies to modulate the current are reviewed.
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Affiliation(s)
- I S Cohen
- Department of Physiology and Biophysics, Stony Brook University, Room 150 Basic Science Tower, Stony Brook, NY 11794-8661, USA
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19
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Altomare C, Tognati A, Bescond J, Ferroni A, Baruscotti M. Direct inhibition of the pacemaker (If) current in rabbit sinoatrial node cells by genistein. Br J Pharmacol 2006; 147:36-44. [PMID: 16273123 PMCID: PMC1615846 DOI: 10.1038/sj.bjp.0706433] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2005] [Revised: 09/14/2005] [Accepted: 09/14/2005] [Indexed: 11/09/2022] Open
Abstract
Genistein is a tyrosine kinase inhibitor which interferes with the activity of several ionic channels either by altering modulatory phosphorylating processes or by direct binding. In whole-cell conditions, genistein induces a partial inhibition of the pacemaker (I(f)) current recorded in cardiac sinoatrial and ventricular myocytes. We investigated the mechanism of action of genistein (50 microM) on the I(f) current in whole-cell, cell-attached, and inside-out configurations, and the measured fractional inhibitions were similar: 26.6, 27.2, and 33.6%, respectively. When ATP was removed from the whole-cell pipette solution no differences were revealed in the effect of the drug when compared to metabolically active cells. Genistein fully maintained its blocking ability even when herbimycin, a tyrosine kinase inhibitor, was added to the whole-cell ATP-free pipette solution. Genistein-induced block was independent of the gating state of the channel and did not display voltage or current dependence; this independence distinguishes genistein from all other f-channel blockers. When inside-out experiments were performed to test for a direct interaction with the channel, genistein, superfused on the intracellular side of the membrane, decreased the maximal I(f) conductance, and slightly shifted the current-activation curve to the left. Furthermore, the effect of genistein was independent of cAMP modulation. We conclude that, in addition to its tyrosine kinase-inhibitory properties, genistein also blocks I(f) by directly interacting with the channel, and thus cannot be considered a valuable pharmacological tool to investigate phosphorylation-dependent modulatory pathways of the I(f) current and of cardiac rhythm.
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Affiliation(s)
- Claudia Altomare
- Department of Biomolecular Sciences and Biotechnology, Laboratory of Molecular Physiology and Neurobiology, University of Milan, via Celoria 26, 20133 Milano, Italy
| | - Agnese Tognati
- Department of Biomolecular Sciences and Biotechnology, Laboratory of Molecular Physiology and Neurobiology, University of Milan, via Celoria 26, 20133 Milano, Italy
| | - Jocelyn Bescond
- Institut de Biologie et Physiologie Cellulaire UMR 6187 CNRS, Université de Poitiers Pôle Biologie Santé, 40 avenue du Recteur Pineau, 86022 Poitiers cedex, France
| | - Arnaldo Ferroni
- Department of Biomolecular Sciences and Biotechnology, Laboratory of Molecular Physiology and Neurobiology, University of Milan, via Celoria 26, 20133 Milano, Italy
| | - Mirko Baruscotti
- Department of Biomolecular Sciences and Biotechnology, Laboratory of Molecular Physiology and Neurobiology, University of Milan, via Celoria 26, 20133 Milano, Italy
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20
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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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21
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Cao XJ, Oertel D. Temperature Affects Voltage-Sensitive Conductances Differentially in Octopus Cells of the Mammalian Cochlear Nucleus. J Neurophysiol 2005; 94:821-32. [PMID: 15800074 DOI: 10.1152/jn.01049.2004] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Temperature is an important physiological variable the influence of which on macroscopic electrophysiological measurements in slices is not well documented. We show that each of three voltage-sensitive conductances of octopus cells of the mammalian ventral cochlear nucleus (VCN) is affected differently by changes in temperature. As expected, the kinetics of the currents were faster at higher than at lower temperature. Where they could be measured, time constants of activation, deactivation, and inactivation had Q10 values between 1.8 and 4.6. The magnitude of the peak conductances was differentially affected by temperature. While the peak magnitude of the high-voltage-activated K+ conductance, gKH, was unaffected by changes in temperature, the peak of the low-voltage-activated K+ conductance, gKL, was reduced by half when the temperature was lowered from 33 to 23°C ( Q10 = 2). Changing the temperature changed the kinetics and the magnitude of the hyperpolarization-activated mixed cation conductance, gh, but the changes in magnitude were transient. The voltage sensitivity of the three conductances was unaffected by temperature. The action of temperature on these conductances is reflected in the resting potentials and in the shapes of action potentials.
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Affiliation(s)
- Xiao-Jie Cao
- Department of Physiology, University of Wisconsin, Madison, Wisconsin 53706, USA
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22
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Frère SGA, Kuisle M, Lüthi A. Regulation of recombinant and native hyperpolarization-activated cation channels. Mol Neurobiol 2005; 30:279-305. [PMID: 15655253 DOI: 10.1385/mn:30:3:279] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2004] [Accepted: 03/22/2004] [Indexed: 11/11/2022]
Abstract
Ionic currents generated by hyperpolarization-activated cation-nonselective (HCN) channels have been principally known as pacemaker h-currents (Ih), because they allow cardiac and neuronal cells to be rhythmically active over precise intervals of time. Presently, these currents are implicated in numerous additional cellular functions, including neuronal integration, synaptic transmission, and sensory reception. These roles are accomplished by virtue of the regulation of Ih by both voltage and ligands. The article summarizes recent developments on the properties and allosteric interactions of these two regulatory pathways in cloned and native channels. Additionally, it discusses how the expression and properties of native channels may be controlled via regulation of the transcription of the HCN channel gene family and the assembly of channel subunits. Recently, several cardiac and neurological diseases were found to be intimately associated with a dysregulation of HCN gene transcription, suggesting that HCN-mediated currents may be involved in the pathophysiology of excitable systems. As a starting point, we briefly review the general characteristics of Ih and the regulatory mechanisms identified in heterologously expressed HCN channels.
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Affiliation(s)
- Samuel G A Frère
- Section of Pharmacology and Neurobiology, Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland
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23
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Wahl-Schott C, Baumann L, Zong X, Biel M. An arginine residue in the pore region is a key determinant of chloride dependence in cardiac pacemaker channels. J Biol Chem 2005; 280:13694-700. [PMID: 15644313 DOI: 10.1074/jbc.m413197200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The modulation of ion channel activity by extracellular ions plays a central role in the control of heart function. Here, we show that the sinoatrial pacemaker current I(f) is strongly affected by the extracellular Cl- concentration. We investigated the molecular basis of the Cl- dependence in heterologously expressed hyperpolarization-activated cyclic nucleotide-gated (HCN) channels that represent the molecular correlate of I(f). Currents carried by the two cardiac HCN channel isoforms (HCN2 and HCN4) showed the same strong Cl- dependence as the sinoatrial I(f) and decreased to about 10% in the absence of external Cl-. In contrast, the neuronal HCN1 current was reduced to only 50% under the same conditions. Depletion of Cl- did not affect the voltage dependence of activation or the ion selectivity of the channels, indicating that the reduction of I(f) was caused by a decrease of channel conductance. A series of chimeras between HCN1 and HCN2 was constructed to identify the structural determinants underlying the different Cl- dependence of HCN1 and HCN2. Exchange of the ion-conducting pore region was sufficient to switch the Cl- dependence from HCN1- to HCN2-type and vice versa. Replacement of a single alanine residue in the pore of HCN1 (Ala-352) by an arginine residue present in HCN2 at equivalent position (Arg-405) induced HCN2-type chloride sensitivity in HCN1. Our data indicate that Arg-405 is a key component of a domain that allosterically couples Cl- binding with channel activation.
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Affiliation(s)
- Christian Wahl-Schott
- Department Pharmazie - Pharmakologie für Naturwissenschaften, Ludwig-Maximilians-Universität München, Butenandtstr. 7-13, 81377 München, Germany
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24
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Wang Y, Wagner MB, Kumar R, Cheng J, Joyner RW. Inhibition of fast sodium current in rabbit ventricular myocytes by protein tyrosine kinase inhibitors. Pflugers Arch 2003; 446:485-91. [PMID: 12719980 DOI: 10.1007/s00424-003-1061-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2003] [Accepted: 03/31/2003] [Indexed: 10/26/2022]
Abstract
The present study investigated the effects of protein tyrosine kinase inhibitors on the fast sodium current ( I(Na)) in rabbit ventricular myocytes. Single rabbit ventricular myocytes were isolated enzymatically using Langendorff perfusion. I(Na) was recorded using the whole-cell patch-clamp technique at room temperature. The protein tyrosine kinase inhibitors genistein, AG957, ST638, and PP2 reversibly inhibited I(Na) in a concentration-dependent manner. At a test pulse potential of -30 mV, genistein (n=7) inhibited I(Na) by 37.7+/-3.2%, 53.4+/-2.5%, and 71.8+/-2.7% at concentrations of 15, 50, and 100 microM, respectively, without changing the voltage dependence of activation, while 100 microM AG957, 100 microM ST638, and 30 microM PP2 inhibited I(Na) by 38.7+/-2.4, 35.8+/-3.4, and 21.1+/-3.9%, respectively. Genistein (100 microM) and AG957 (100 microM) shifted the voltage for half-maximal inactivation of I(Na) from -76.7+/-2.0 mV (n=10) in control to -88.37+/-2.6 mV (n=6, P<0.05), and -82.9+/-1.7 (n=4, P<0.05), respectively, without changing the slope factor. Genistein and AG957 also significantly prolonged the time course of I(Na) recovery from inactivation. Daidzein and PP3, inactive analogs of genistein and PP2, respectively, did not inhibit I(Na) significantly. We conclude that protein tyrosine kinase signaling pathways may play an important role in regulation of I(Na) in cardiac myocytes.
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Affiliation(s)
- Yanggan Wang
- Todd Franklin Cardiac Research Laboratory, The Sibley Heart Center, Department of Pediatrics, Emory University, 2040 Ridgewood Dr. NE, Atlanta, GA 30322, USA
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25
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Robinson RB, Siegelbaum SA. Hyperpolarization-activated cation currents: from molecules to physiological function. Annu Rev Physiol 2003; 65:453-80. [PMID: 12471170 DOI: 10.1146/annurev.physiol.65.092101.142734] [Citation(s) in RCA: 888] [Impact Index Per Article: 42.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Hyperpolarization-activated cation currents, termed If, Ih, or Iq, were initially discovered in heart and nerve cells over 20 years ago. These currents contribute to a wide range of physiological functions, including cardiac and neuronal pacemaker activity, the setting of resting potentials, input conductance and length constants, and dendritic integration. The hyperpolarization-activated, cation nonselective (HCN) gene family encodes the channels that underlie Ih. Here we review the relation between the biophysical properties of recombinant HCN channels and the pattern of HCN mRNA expression with the properties of native Ih in neurons and cardiac muscle. Moreover, we consider selected examples of the expanding physiological functions of Ih with a view toward understanding how the properties of HCN channels contribute to these diverse functional roles.
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Affiliation(s)
- Richard B Robinson
- Department of Pharmacology, Center for Molecular Therapeutics, Columbia University, New York, NY 10032, USA.
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26
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Akaishi Y, Hattori Y, Yoshimoto K, Kitabatake A, Yasuda K, Kanno M. Involvement of tyrosine phosphorylation in the positive inotropic effect produced by H(1)-receptors with histamine in guinea-pig left atrium. Br J Pharmacol 2000; 130:907-15. [PMID: 10864899 PMCID: PMC1572121 DOI: 10.1038/sj.bjp.0703355] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
We investigated the effect of stimulation of H(1)-receptors with histamine on protein tyrosine phosphorylation levels in guinea-pig left atrium and evaluated the influences of tyrosine kinase inhibitors on the positive inotropic effect mediated by H(1)-receptors in this tissue. Histamine induced an increase in tyrosine phosphorylation in four main clusters of proteins with apparent molecular weights of 25, 35, 65 and 150 kDa. Tyrosine phosphorylation of these proteins attained a peak around 2 - 3 min following histamine stimulation and then declined to or below basal levels. Histamine-induced protein tyrosine phosphorylation was antagonized by the H(1)-receptor antagonists mepyramine (1 microM) and chlorpheniramine (1 microM), but not by the H(2)-receptor antagonist cimetidine (10 microM). The positive inotropic effect of histamine was depressed in a concentration-dependent manner by the tyrosine kinase inhibitors tyrphostin A25 (50 to 100 microM) and genistein (10 to 50 microM) but not by the inactive genistein analogue daidzein (50 microM). The positive inotropic effect of isoprenaline was unchanged by tyrphostin A25 and genistein. At a concentration of 1 microM histamine produced a dual-component positive inotropic response composed of an initial increasing phase and a second and late developing, greater positive inotropic phase. Treatment with tyrphostin A25 (100 microM) and genistein (50 microM), but not daidzein (50 microM), significantly attenuated the two components of the inotropic response, although genistein suppressed the initial component more markedly than the late component. We conclude that increased protein tyrosine phosphorylation may play an important role in initiating at least some part of the positive inotropic effect of H(1)-receptor stimulation in guinea-pig left atrium.
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Affiliation(s)
- Y Akaishi
- Department of Pharmacology, Hokkaido University School of Medicine, Sapporo 060-8638, Japan
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27
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Wu JY, Yu H, Cohen IS. Epidermal growth factor increases i(f) in rabbit SA node cells by activating a tyrosine kinase. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1463:15-9. [PMID: 10631290 DOI: 10.1016/s0005-2736(99)00233-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Our previous results have demonstrated that tyrosine kinase inhibition reduces i(f) in rabbit SA node myocytes, suggesting that tyrosine kinases regulate i(f). One receptor tyrosine kinase the EGF receptor kinase is known to increase heart rate. To determine if this action is mediated through changes in i(f), we examined the effect of epidermal growth factor (EGF) on i(f) with the permeabilized patch-clamp technique. 0.1 microM EGF increased i(f) amplitude in response to single-step hyperpolarizations in the diastolic range of potentials. This increase was 20+/-3%, n=11 at -75 mV. This effect is caused by activating a tyrosine kinase because 50 microM genistein, a tyrosine kinase inhibitor, eliminated this EGF action. A two-step pulse protocol showed that maximal i(f) conductance was increased by EGF. We further examined this conductance change by constructing the activation curve. The maximal i(f) conductance was increased by 23% with no change in midpoint, V(1/2), control=-74+/-2 mV, V(1/2) EGF=-74+/-1 mV. Thus EGF acts via a tyrosine kinase to increase maximal i(f) conductance with no change in the voltage dependence of activation. These results suggest that EGF effects on i(f) contribute to the positive chronotropic effect of EGF on SA node.
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Affiliation(s)
- J Y Wu
- Department of Physiology and Biophysics, Health Sciences Center, SUNY at Stony Brook, Stony Brook, NY 11794-8661, USA
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28
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Shibata S, Ono K, Iijima T. Inhibition by genistein of the hyperpolarization-activated cation current in porcine sino-atrial node cells. Br J Pharmacol 1999; 128:1284-90. [PMID: 10578143 PMCID: PMC1571748 DOI: 10.1038/sj.bjp.0702903] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1 The hyperpolarization-activated cation current (If) was recorded in single pacemaker cells of the porcine sino-atrial node, and the effects of genistein, an isoflavone inhibitor of tyrosine-specific protein kinases was investigated by the whole-cell patch clamp technique. 2 Genistein (20-500 microM) decreased If in a dose-dependent manner with an IC50 value of 62.3 microM and a maximum inhibition of 45.3%. 3 The effect on If appeared without altering the half-activation potential (control, -88.3+/-2.8 mV; genistein, -87.0+/-1.8 mV) and the slope factor (control, 8.0+/-0.3 mV; genistein, 8.6+/-0.7 mV) of the steady-state activation curve. No significant voltage-dependency was detected in the fully-activated current-voltage relation measured by the double-pulse protocols. 4 The inactive form of genistein analogue, daidzein (500 microM) or genistin (200 microM), were without effect. If was not affected by another tyrosine kinase inhibitor, tryphostin-47 (100 microM), but tyrphostin-25 (100-200 microM) suppressed If in an irreversible manner. 5 Neither bath nor intracellular application of the tyrosine phosphatase inhibitor, orthovanadate, affected If, and subsequent application of genistein inhibited If significantly. 6 These data indicate that the inhibition of If by genistein is not mediated through tyrosine kinase inhibition but through nonselective block of the If channels.
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Affiliation(s)
- Shigehiro Shibata
- Department of Pharmacology, Akita University School of Medicine, Akita 010-8543, Japan
| | - Kyoichi Ono
- Department of Pharmacology, Akita University School of Medicine, Akita 010-8543, Japan
| | - Toshihiko Iijima
- Department of Pharmacology, Akita University School of Medicine, Akita 010-8543, Japan
- Author for correspondence:
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Gasparini S, DiFrancesco D. Action of serotonin on the hyperpolarization-activated cation current (Ih) in rat CA1 hippocampal neurons. Eur J Neurosci 1999; 11:3093-100. [PMID: 10510173 DOI: 10.1046/j.1460-9568.1999.00728.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
We studied the effects of serotonin (5-HT) on hippocampal CA1 pyramidal neurons. In current-clamp mode, 5-HT induced a hyperpolarization and reduction of excitability due to the opening of inward rectifier K+ channels, followed by a late depolarization and partial restoration of excitability. These two components could be dissociated, as in the presence of BaCl2 to block K+ channels, 5-HT induced a depolarization accompanied by a reduction of membrane resistance, whereas in the presence of ZD 7288 [4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyrimidinium chloride], a selective blocker of the hyperpolarization-activated cation current (Ih), 5-HT only hyperpolarized neurons. We then studied the action of 5-HT on Ih in voltage-clamp conditions. 5-HT increased Ih at -90 mV by 29.1 +/- 2.9% and decreased the time constant of activation by 20.1 +/- 1.7% (n = 16), suggesting a shift in the voltage dependence of the current towards more positive potentials; however, the fully activated current measured at -140 mV also increased (by 14.1 +/- 1.7%, n = 14); this increase was blocked by ZD 7288, implying an effect of 5-HT on the maximal conductance of Ih. Both the shift of activation curve and the increase in maximal conductance were confirmed by data obtained with ramp protocols. Perfusion with the membrane-permeable analogue of cAMP, 8-bromoadenosine 3'5'-cyclic monophosphate (8-Br-cAMP), increased Ih both at -90 and -140 mV, although the changes induced were smaller than those due to 5-HT. Our data indicate that 5-HT modulates Ih by shifting its activation curve to more positive voltages and by increasing its maximal conductance, and that this action is likely to contribute to the 5-HT modulation of excitability of CA1 cells.
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Affiliation(s)
- S Gasparini
- Università degli Studi di Milano, Dipartimento di Fisiologia e Biochimica General, Elettrofisiologia, Italy.
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Santoro B, Tibbs GR. The HCN gene family: molecular basis of the hyperpolarization-activated pacemaker channels. Ann N Y Acad Sci 1999; 868:741-64. [PMID: 10414361 DOI: 10.1111/j.1749-6632.1999.tb11353.x] [Citation(s) in RCA: 283] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The molecular basis of the hyperpolarization-activated cation channels that underlie the anomalous rectifying current variously termed Ih, Iq, or I(f) is discussed. On the basis of the expression patterns and biophysical properties of the newly cloned HCN ion channels, an initial attempt at defining the identity and subunit composition of channels underlying native Ih is undertaken. By comparing the sequences of HCN channels to other members of the K channel superfamily, we discuss how channel opening may be coupled to membrane hyperpolarization and to direct binding of cyclic nucleotide. Finally, we consider some of the questions in cardiovascular physiology and neurobiology that can be addressed as a result of the demonstration that Ih is encoded by the HCN gene family.
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Affiliation(s)
- B Santoro
- Center for Neurobiology and Behavior, Columbio University, New York, New York 10032, USA
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