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Gross C, Saponaro A, Santoro B, Moroni A, Thiel G, Hamacher K. Mechanical transduction of cytoplasmic-to-transmembrane-domain movements in a hyperpolarization-activated cyclic nucleotide-gated cation channel. J Biol Chem 2018; 293:12908-12918. [PMID: 29936413 PMCID: PMC6102142 DOI: 10.1074/jbc.ra118.002139] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2018] [Revised: 06/05/2018] [Indexed: 01/26/2023] Open
Abstract
Hyperpolarization-activated cyclic nucleotide–gated cation (HCN) channels play a critical role in the control of pacemaking in the heart and repetitive firing in neurons. In HCN channels, the intracellular cyclic nucleotide–binding domain (CNBD) is connected to the transmembrane portion of the channel (TMPC) through a helical domain, the C-linker. Although this domain is critical for mechanical signal transduction, the conformational dynamics in the C-linker that transmit the nucleotide-binding signal to the HCN channel pore are unknown. Here, we use linear response theory to analyze conformational changes in the C-linker of the human HCN1 protein, which couple cAMP binding in the CNBD with gating in the TMPC. By applying a force to the tip of the so-called “elbow” of the C-linker, the coarse-grained calculations recapitulate the same conformational changes triggered by cAMP binding in experimental studies. Furthermore, in our simulations, a displacement of the C-linker parallel to the membrane plane (i.e. horizontally) induced a rotational movement resulting in a distinct tilting of the transmembrane helices. This movement, in turn, increased the distance between the voltage-sensing S4 domain and the surrounding transmembrane domains and led to a widening of the intracellular channel gate. In conclusion, our computational approach, combined with experimental data, thus provides a more detailed understanding of how cAMP binding is mechanically coupled over long distances to promote voltage-dependent opening of HCN channels.
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Affiliation(s)
- Christine Gross
- Computational Biology and Simulation Group, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | - Andrea Saponaro
- Department of Biosciences, University of Milan, 20133 Milan, Italy
| | - Bina Santoro
- Department of Neuroscience, Columbia University, New York, New York 10032
| | - Anna Moroni
- Department of Biosciences, University of Milan, 20133 Milan, Italy
| | - Gerhard Thiel
- Membrane Biophysics, Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany.
| | - Kay Hamacher
- Computational Biology and Simulation Group, Technische Universität Darmstadt, 64287 Darmstadt, Germany
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Abstract
Electronic pacemakers have been used in patients with heart rhythm disorders for device-supported pacing. While effective, there are such shortcomings as limited battery life, permanent implantation of catheters, the lack of autonomic neurohumoral responses, and risks of lead dislodging. Here we describe protocols for establishing porcine models of sick sinus syndrome and complete heart block, and the generation of bioartificial pacemaker by delivering a strategically engineered form of hyperpolarization-activated cyclic nucleotide-gated pacemaker channel protein via somatic gene transfer to convert atrial or ventricular muscle cardiomyocytes into nodal-like cells that rhythmically fire action potentials.
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3
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AAV-mediated conversion of human pluripotent stem cell-derived pacemaker. Biochem Biophys Res Commun 2017; 494:346-351. [DOI: 10.1016/j.bbrc.2017.10.023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Accepted: 10/04/2017] [Indexed: 12/21/2022]
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Wang Y, Cong B, Shen J, Liu S, Liu F, Wang N, Huang X. Molecular cloning and functional analysis of a voltage-gated potassium channel in lymphocytes from sea perch, Lateolabrax japonicus. FISH & SHELLFISH IMMUNOLOGY 2012; 33:605-613. [PMID: 22651989 DOI: 10.1016/j.fsi.2012.05.024] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2012] [Revised: 03/22/2012] [Accepted: 05/14/2012] [Indexed: 06/01/2023]
Abstract
Voltage-gated potassium (Kv) channels on cell plasma membrane play an important role in both excitable cells and non-excitable cells and Kv1 subfamily is most extensively studied channel in mammalian cells. Recently, this potassium channel was reported to control processes inside mammalian T lymphocytes such as cell proliferation and volume regulation. Little is known about Kv1 channels in fish. We have postulated the presence of such a channel in lymphocytes and speculated its potential role in immunoregulation in fish. Employing specific primers and RNA template, we cloned a segment of a novel gene from sea perch blood sample and subsequently obtained a full cDNA sequence using RACE approach. Bioinformatic analysis revealed structural and phylogenetic characteristics of a novel Kv channel gene, designated as spKv1.3, which exhibits homologous domains to the members of Kv1.3 family, but it differs notably from some other members of that family at the carboxyl terminus. Full-length of spKv1.3 cDNA is 2152 bp with a 1440 bp open reading frame encoding a protein of 480 amino acids. SpKv1.3 gene is expressed in all of the tested organs and tissues of sea perch. To assess the postulated immune function of spKv1.3, we stimulated lymphocytes with LPS and/or channel blocker 4-AP. Expression levels of messenger RNA (mRNA) of spKv1.3 under stimulation conditions were measured by quantitative RT-PCR. The results showed that LPS can motivate the up-regulation of spKv1.3 expression significantly. Interestingly, we found for the first time that 4-AP with LPS can also increase the spKv1.3 mRNA expression levels in time course. Although 4-AP could block potassium channels physically, we speculated that its effect on blockage of potassium channel may start up an alternative mechanism which feed back and evoke the spKv1.3 mRNA expression.
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Affiliation(s)
- Yongjie Wang
- Key Laboratory of Marine Bioactive Substance, State Oceanic Administration, Qingdao 266061, PR China
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5
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Li RA. Gene- and cell-based bio-artificial pacemaker: what basic and translational lessons have we learned? Gene Ther 2012; 19:588-95. [PMID: 22673497 DOI: 10.1038/gt.2012.33] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Normal rhythms originate in the sino-atrial node, a specialized cardiac tissue consisting of only a few thousands of nodal pacemaker cells. Malfunction of pacemaker cells due to diseases or aging leads to rhythm generation disorders (for example, bradycardias and sick-sinus syndrome (SSS)), which often necessitate the implantation of electronic pacemakers. Although effective, electronic devices are associated with such shortcomings as limited battery life, permanent implantation of leads, lead dislodging, the lack of autonomic responses and so on. Here, various gene- and cell-based approaches, with a particular emphasis placed on the use of pluripotent stem cells and the hyperpolarization-activated cyclic nucleotide-gated-encoded pacemaker gene family, that have been pursued in the past decade to reconstruct bio-artificial pacemakers as alternatives will be discussed in relation to the basic biological insights and translational regenerative potential.
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Affiliation(s)
- R A Li
- Center of Cardiovascular Research, Mount Sinai School of Medicine, New York, NY 10029, USA.
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Sand RM, Atherton DM, Spencer AN, Gallin WJ. jShaw1, a low-threshold, fast-activating K(v)3 from the hydrozoan jellyfish Polyorchis penicillatus. ACTA ACUST UNITED AC 2011; 214:3124-37. [PMID: 21865525 DOI: 10.1242/jeb.057000] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Voltage-gated potassium (K(v)) channels work in concert with other ion channels to determine the frequency and duration of action potentials in excitable cells. Little is known about K(v)3 channels from invertebrates, but those that have been characterized generally display slow kinetics. Here, we report the cloning and characterization of jShaw1, the first K(v)3 isolated from a cnidarian, the jellyfish Polyorchis penicillatus, in comparison with mouse K(v)3.1 and K(v)3.2. Using a two-electrode voltage clamp on Xenopus laevis oocytes expressing the channels, we compared steady-state and kinetic properties of macroscopic currents. jShaw1 is fast activating, and opens at potentials approximately 40 mV more hyperpolarized than the mouse K(v)3 channels. There is an inverse relationship between the number of positive charges on the voltage sensor and the half-activation voltage of the channel, contrary to what would be expected with the simplest model of voltage sensitivity. jShaw1 has kinetic characteristics that are substantially different from the mammalian K(v)3 channels, including a much lower sensitivity of early activation rates to incremental voltage changes, and a much faster voltage-dependent transition in the last stages of opening. jShaw1 opening kinetics were affected little by pre-depolarization voltage, in contrast to both mouse channels. Similar to the mouse channels, jShaw1 was half-blocked by 0.7 mmol l(-1) tetraethyl ammonium and 5 mmol l(-1) 4-aminopyridine. Comparison of sequence and functional properties of jShaw1 with the mouse and other reported K(v)3 channels helps to illuminate the general relationship between amino acid sequence and electrophysiological activity in this channel family.
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Affiliation(s)
- Rheanna M Sand
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
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Bazyan AS, Segal OL. Hyperpolarization-activated I h pacemaker channel in the mammalian brain. NEUROCHEM J+ 2010. [DOI: 10.1134/s181971241004001x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Chan YC, Wang K, Au KW, Au KW, Lau CP, Tse HF, Li RA. Probing the bradycardic drug binding receptor of HCN-encoded pacemaker channels. Pflugers Arch 2010; 459:25-38. [PMID: 19756722 PMCID: PMC2765624 DOI: 10.1007/s00424-009-0719-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Revised: 07/23/2009] [Accepted: 08/21/2009] [Indexed: 11/26/2022]
Abstract
If (or Ih), encoded by the hyperpolarization-activated, cyclic nucleotide-gated (HCN1–4) channel gene family, contributes significantly to cardiac pacing. Bradycardic agents such as ZD7288 that target HCN channels have been developed, but the molecular configuration of their receptor is poorly defined. Here, we probed the drug receptor by systematically introducing alanine scanning substitutions into the selectivity filter (C347A, I348A, G349A, Y350A, G351A in the P-loop), outer (P355A, V356A, S357A, M358A in the P-S6 linker), and inner (M377A, F378A, V379A in S6) pore vestibules of HCN1 channels. When heterologously expressed in human embryonic kidney 293 cells for patch-clamp recordings, I348A, G349A, Y350A, G351A, P355A, and V356A did not produce measurable currents. The half-blocking concentration (IC50) of wild type (WT) for ZD7288 was 25.8 ± 9.7 μM. While the IC50 of M358A was identical to WT, those of C347A, S357A, F378A, and V379A markedly increased to 137.6 ± 56.4, 113.3 ± 34.1, 587.1 ± 167.5, and 1726.3 ± 673.4 μM, respectively (p < 0.05). Despite the proximity of the S6 residues studied, M377A was hypersensitive (IC50 = 5.1 ± 0.7 μM; p < 0.05) implicating site specificity. To explore the energetic interactions among the S6 residues, double and triple substitutions (M377A/F378A, M377A/V379A, F378A/V379A, and M377A/F378A/V379A) were generated for thermodynamic cycle analysis. Specific interactions with coupling energies (ΔΔG) >1 kT for M377–F378 and F378–V379 but not M377–V379 were identified. Based on these new data and others, we proposed a refined drug-blocking model that may lead to improved antiarrhythmics and bioartificial pacemaker designs.
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Affiliation(s)
- Yau-Chi Chan
- Division of Cardiology, Department of Medicine, Queen Mary Hospital, Li Ka Shing Faculty of Medicine, University of Hong Kong, Pokfulam, Hong Kong
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Chan YC, Siu CW, Lau YM, Lau CP, Li RA, Tse HF. Synergistic effects of inward rectifier (I) and pacemaker (I) currents on the induction of bioengineered cardiac automaticity. J Cardiovasc Electrophysiol 2009; 20:1048-54. [PMID: 19460073 DOI: 10.1111/j.1540-8167.2009.01475.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
INTRODUCTION Normal heart rhythms originate in the sinoatrial node. HCN-encoded funny current (I(f)) and the Kir2-encoded inward rectifier (I(K1)) counteract each other by respectively oscillating and stabilizing the negative resting membrane potential, and controlling action potential firing. Therefore, I(K1) suppression and I(f) overexpression have been independently exploited to convert cardiomyocytes (CMs) into AP-firing bioartificial pacemakers. Although the 2 strategies have been largely assumed synergistic, their complementarity has not been investigated. METHODS AND RESULTS We explored the interrelationships of automaticity, I(f) and I(K1) by transducing single left ventricular (LV) CMs isolated from guinea pig hearts with the recombinant adenoviruses Ad-CMV-GFP-IRES-HCN1-AAA and/or Ad-CGI-Kir2.1 to mediate their current densities via a whole-cell patch clamp technique at 37 degrees C. Results showed that Ad-CGI-HCN1-AAA but not Ad-CGI-Kir2.1 transduction induced automaticity (181.1 +/- 13.1 bpm). Interestingly, Ad-CGI-HCN1-AAA/Ad-CGI-Kir2.1 cotransduction significantly promoted the induced firing frequency (320.0 +/- 15.8 bpm; P < 0.05). Correlation analysis revealed that the firing frequency, phase-4 slope and APD(90) of AP-firing LV CMs were correlated with I(f) (R(2) > 0.7) only when -2 >I(K1) >-4 pA/pF but not with I(K1) over the entire I(f) ranges examined (0.02 < R(2) < 0.4). Unlike I(f), I(K1) displayed correlation with neither the phase-4 slope (R(2)= 0.02) nor phase-4 length (R(2)= 0.04) when -2 > I(f) > -4 pA/pF. As anticipated, however, APD(90) was correlated with I(K1) (R(2)= 0.4). CONCLUSION We conclude that an optimal level of I(K1) maintains a voltage range for I(f) to operate most effectively during a dynamic cardiac cycle.
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Affiliation(s)
- Yau-Chi Chan
- Cardiology Division, Department of Medicine, University of Hong Kong, Hong Kong
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Lieu DK, Chan YC, Lau CP, Tse HF, Siu CW, Li RA. Overexpression of HCN-encoded pacemaker current silences bioartificial pacemakers. Heart Rhythm 2008; 5:1310-7. [PMID: 18693074 DOI: 10.1016/j.hrthm.2008.05.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/12/2007] [Accepted: 05/10/2008] [Indexed: 11/17/2022]
Abstract
BACKGROUND Current strategies of engineering bioartificial pacemakers from otherwise silent yet excitable adult atrial and ventricular cardiomyocytes primarily rely on either maximizing the hyperpolarization-activated I(f) or on minimizing its presumptive opponent, the inwardly rectifying potassium current I(K1). OBJECTIVE The purpose of this study was to determine quantitatively the relative current densities of I(f) and I(K1) necessary to induce automaticity in adult atrial cardiomyocytes. METHODS Automaticity of adult guinea pig atrial cardiomyocytes was induced by adenovirus (Ad)-mediated overexpression of the gating-engineered HCN1 construct HCN1-DeltaDeltaDelta with the S3-S4 linker residues EVY235-7 deleted to favor channel opening. RESULTS Whereas control atrial cardiomyocytes remained electrically quiescent and had no I(f), 18% of Ad-CMV-GFP-IRES-HCN1-DeltaDeltaDelta (Ad-CGI-HCN1-DeltaDeltaDelta)-transduced cells demonstrated automaticity (240 +/- 14 bpm) with gradual phase 4 depolarization (143 +/- 28 mV/s), a depolarized maximal diastolic potential (-45.3 +/- 2.2 mV), and substantial I(f) at -140 mV (I(f,-140 mV) = -9.32 +/- 1.84 pA/pF). In the remaining quiescent Ad-CGI-HCN1-DeltaDeltaDelta-transduced atrial cardiomyocytes, two distinct immediate phenotypes were observed: (1) 13% had a hyperpolarized resting membrane potential (-56.7 +/- 1.3 mV) with I(f,-140 mV) of -4.85 +/- 0.97 pA/pF; and (2) the remaining 69% displayed a depolarized resting membrane potential (-27.6 +/- 1.3 mV) with I(f,-140 mV) of -23.0 +/- 3.71 pA/pF. Upon electrical stimulation, both quiescent groups elicited a single action potential with incomplete phase 4 depolarization that was never seen in controls. Further electrophysiologic analysis indicates that an intricate balance of I(K1) and I(f) is necessary for induction of atrial automaticity. CONCLUSION Optimized pacing induction and modulation can be better achieved by engineering the I(f)/I(K1) ratio rather than the individual currents.
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Affiliation(s)
- Deborah K Lieu
- Stem Cell Program, University of California, Davis, California, USA
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Siu CW, Lieu DK, Li RA. HCN-encoded pacemaker channels: from physiology and biophysics to bioengineering. J Membr Biol 2007; 214:115-22. [PMID: 17558529 DOI: 10.1007/s00232-006-0881-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2006] [Revised: 11/24/2006] [Indexed: 12/15/2022]
Abstract
The depolarizing membrane ionic current I(h) (also known as I(f), "f" for funny), encoded by the hyperpolarization-activated cyclic-nucleotide-modulated (HCN1-4) channel gene family, was first discovered in the heart over 25 years ago. Later, I(h) was also found in neurons, retina, and taste buds. HCN channels structurally resemble voltage-gated K(+) (Kv) channels but the molecular features underlying their opposite gating behaviors (activation by hyperpolarization rather than depolarization) and non-selective permeation profiles (> or =25 times less selective for K(+) than Kv channels) remain largely unknown. Although I(h) has been functionally linked to biological processes from the autonomous beating of the heart to pain transmission, the underlying mechanistic actions remain largely inferential and, indeed, somewhat controversial due to the slow kinetics and negative operating voltage range relative to those of the bioelectrical events involved (e.g., cardiac pacing). This article reviews the current state of our knowledge in the structure-function properties of HCN channels in the context of their physiological functions and potential HCN-based therapies via bioengineering.
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Affiliation(s)
- C-W Siu
- Stem Cell Program, University of California, Davis, CA 95817, USA
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12
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Ouyang Q, Goeritz M, Harris-Warrick RM. Panulirus interruptus Ih-channel gene PIIH: modification of channel properties by alternative splicing and role in rhythmic activity. J Neurophysiol 2007; 97:3880-92. [PMID: 17409170 DOI: 10.1152/jn.00246.2007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We cloned 10 full-length variants of PIIH, the gene for I(h) from the spiny lobster, Panulirus interruptus, using reverse transcription-PCR (RT-PCR) and rapid amplification of cDNA ends (RACE). This gene shows a significant amount of alternative splicing in the S3-S4 and S4-S5 linkers, in the P-loop and the entire S6 transmembrane domain, in the cyclic nucleotide binding domain (CNBD), and near the 3' end of the gene. Functional expression of seven splice variants in Xenopus oocytes generated slowly activating hyperpolarization-activated inward currents, which were blocked by the I(h) channel blockers CsCl and ZD7288. The different splice variants had markedly varying activation kinetics and voltage dependence of activation. Bath application of 8-Br-cAMP shifted the V(1/2) to more positive potentials and accelerated the activation kinetics in an isoform-specific manner. Two variants containing a segment with an ER-retention motif in the S4-S5 loop did not produce currents in oocytes. Overexpression of one splice variant, PIIH AB(S)-I, in pyloric dilator (PD) neurons in the lobster stomatogastric ganglion produced an average threefold increase in I(h) without evoking a compensatory increase in I(A). The voltage for half-maximal activation of I(h) in PIIH AB(S)-I-expressing PDs was shifted in the depolarizing direction by 9 mV, whereas the slope factor decreased by 3.8 mV. Moreover, its activation kinetics were significantly faster than in control PDs. PIIH AB(S)-I overexpression enhanced PD neuron rhythmic firing in an amplitude-dependent manner above a minimal threshold two- to threefold increase in amplitude.
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Affiliation(s)
- Qing Ouyang
- Dept. of Neurobiology and Behavior, Cornell University, W159 Seeley G. Mudd Hall, Ithaca, NY 14853. )
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Xue T, Siu CW, Lieu DK, Lau CP, Tse HF, Li RA. Mechanistic role of I(f) revealed by induction of ventricular automaticity by somatic gene transfer of gating-engineered pacemaker (HCN) channels. Circulation 2007; 115:1839-50. [PMID: 17389267 PMCID: PMC2698014 DOI: 10.1161/circulationaha.106.659391] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Although I(f), encoded by the hyperpolarization-activated cyclic-nucleotide-modulated (HCN) channel gene family, is known to be functionally important in pacing, its mechanistic action is largely inferential and indeed somewhat controversial. To dissect in detail the role of I(f), we investigated the functional consequences of overexpressing in adult guinea pig left ventricular cardiomyocytes (LVCMs) various HCN1 constructs that have been engineered to exhibit different gating properties. METHODS AND RESULTS We created the recombinant adenoviruses Ad-CMV-GFP-IRES (CGI), Ad-CGI-HCN1, Ad-CGI-HCN1-delta delta delta, and Ad-CGI-HCN1-Ins, which mediate ectopic expression of GFP alone, WT, EVY235-7delta delta delta, and Ins HCN1 channels, respectively; EVY235-7delta delta delta and Ins encode channels in which the S3-S4 linkers have been shortened and lengthened to favor and inhibit opening, respectively. Ad-CGI-HCN1, Ad-CGI-HCN1-delta delta delta, and Ad-CGI-HCN1-Ins, but not control Ad-CGI, transduction of LVCMs led to robust expression of I(f) with comparable densities when fully open (approximately = -22 pA/pF at -140 mV; P>0.05) but distinctive activation profiles (V(1/2) = -70.8+/-0.6, -60.4+/-0.7, and -87.7+/-0.7 mV; P<0.01, respectively). Whereas control (nontransduced or Ad-CGI-transduced) LVCMs were electrically quiescent, automaticity (206+/-16 bpm) was observed exclusively in 61% of Ad-HCN1-delta delta delta-transduced cells that displayed depolarized maximum diastolic potential (-60.6+/-0.5 versus -70.6+/-0.6 mV of resting membrane potential of control cells; P<0.01) and gradual phase 4 depolarization (306+/-32 mV/s) that were typical of genuine nodal cells. Furthermore, spontaneously firing Ad-HCN1-delta delta delta-transduced LVCMs responded positively to adrenergic stimulation (P<0.05) but exhibited neither overdrive excitation nor suppression. In contrast, the remaining 39% of Ad-HCN1-delta delta delta-transduced cells exhibited no spontaneous action potentials; however, a single ventricular action potential associated with a depolarized resting membrane potential and a unique, incomplete "phase 4-like" depolarization that did not lead to subsequent firing could be elicited on simulation. Such an intermediate phenotype, similarly observed in 100% of Ad-CGI-HCN- and Ad-CGI-HCN1-Ins-transduced LVCMs, could be readily reversed by ZD7288, hinting at a direct role of I(f). Correlation analysis revealed the specific biophysical parameters required for I(f) to function as an active membrane potential oscillator. CONCLUSIONS Our results not only contribute to a better understanding of cardiac pacing but also may advance current efforts that focus primarily on automaticity induction to the next level by enabling bioengineering of central and peripheral cells that make up the native sinoatrial node.
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Affiliation(s)
- Tian Xue
- Department of Cell Biology and Human Anatomy, University of California, Davis, USA
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Tse HF, Xue T, Lau CP, Siu CW, Wang K, Zhang QY, Tomaselli GF, Akar FG, Li RA. Bioartificial sinus node constructed via in vivo gene transfer of an engineered pacemaker HCN Channel reduces the dependence on electronic pacemaker in a sick-sinus syndrome model. Circulation 2006; 114:1000-11. [PMID: 16923751 DOI: 10.1161/circulationaha.106.615385] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND The normal cardiac rhythm originates in the sinoatrial (SA) node that anatomically resides in the right atrium. Malfunction of the SA node leads to various forms of arrhythmias that necessitate the implantation of electronic pacemakers. We hypothesized that overexpression of an engineered HCN construct via somatic gene transfer offers a flexible approach for fine-tuning cardiac pacing in vivo. METHODS AND RESULTS Using various electrophysiological and mapping techniques, we examined the effects of in situ focal expression of HCN1-DeltaDeltaDelta, the S3-S4 linker of which has been shortened to favor channel opening, on impulse generation and conduction. Single left ventricular cardiomyocytes isolated from guinea pig hearts preinjected with the recombinant adenovirus Ad-CMV-GFP-IRES-HCN1-DeltaDeltaDelta in vivo uniquely exhibited automaticity with a normal firing rate (237+/-12 bpm). High-resolution ex vivo optical mapping of Ad-CGI-HCN1-DeltaDeltaDelta-injected Langendorff-perfused hearts revealed the generation of spontaneous action potentials from the transduced region in the left ventricle. To evaluate the efficacy of our approach for reliable atrial pacing, we generated a porcine model of sick-sinus syndrome by guided radiofrequency ablation of the native SA node, followed by implantation of a dual-chamber electronic pacemaker to prevent bradycardia-induced hemodynamic collapse. Interestingly, focal transduction of Ad-CGI-HCN1-DeltaDeltaDelta in the left atrium of animals with sick-sinus syndrome reproducibly induced a stable, catecholamine-responsive in vivo "bioartificial node" that exhibited a physiological heart rate and was capable of reliably pacing the myocardium, substantially reducing electronic pacing. CONCLUSIONS The results of the present study provide important functional and mechanistic insights into cardiac automaticity and have further refined an HCN gene-based therapy for correcting defects in cardiac impulse generation.
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Affiliation(s)
- Hung-Fat Tse
- Department of Medicine, Queen Mary Hospital, University of Hong Kong, Hong Kong
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