Overexpression of HCN-encoded pacemaker current silences bioartificial pacemakers

Deborah Lieu, Yau Chi Chan, Chu Pak Lau, Hung Fat Tse, Chung Wah Siu, Ronald A. Li

Research output: Contribution to journalArticle

27 Citations (Scopus)

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 If or on minimizing its presumptive opponent, the inwardly rectifying potassium current IK1. Objective: The purpose of this study was to determine quantitatively the relative current densities of If and IK1 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-ΔΔΔ with the S3-S4 linker residues EVY235-7 deleted to favor channel opening. Results: Whereas control atrial cardiomyocytes remained electrically quiescent and had no If, 18% of Ad-CMV-GFP-IRES-HCN1-ΔΔΔ (Ad-CGI-HCN1-ΔΔΔ)-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 If at -140 mV (If,-140 mV = -9.32 ± 1.84 pA/pF). In the remaining quiescent Ad-CGI-HCN1-ΔΔΔ-transduced atrial cardiomyocytes, two distinct immediate phenotypes were observed: (1) 13% had a hyperpolarized resting membrane potential (-56.7 ± 1.3 mV) with If,-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 If,-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 IK1 and If is necessary for induction of atrial automaticity. Conclusion: Optimized pacing induction and modulation can be better achieved by engineering the If/IK1 ratio rather than the individual currents.

Original languageEnglish (US)
Pages (from-to)1310-1317
Number of pages8
JournalHeart Rhythm
Volume5
Issue number9
DOIs
StatePublished - Sep 2008

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Cardiac Myocytes
Adenoviridae
Membrane Potentials
Specific Gravity
Electric Stimulation
Action Potentials
Potassium
Guinea Pigs
Phenotype

Keywords

  • Gene transfer
  • HCN channel
  • Pacemaker

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine

Cite this

Overexpression of HCN-encoded pacemaker current silences bioartificial pacemakers. / Lieu, Deborah; Chan, Yau Chi; Lau, Chu Pak; Tse, Hung Fat; Siu, Chung Wah; Li, Ronald A.

In: Heart Rhythm, Vol. 5, No. 9, 09.2008, p. 1310-1317.

Research output: Contribution to journalArticle

Lieu, Deborah ; Chan, Yau Chi ; Lau, Chu Pak ; Tse, Hung Fat ; Siu, Chung Wah ; Li, Ronald A. / Overexpression of HCN-encoded pacemaker current silences bioartificial pacemakers. In: Heart Rhythm. 2008 ; Vol. 5, No. 9. pp. 1310-1317.
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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 If or on minimizing its presumptive opponent, the inwardly rectifying potassium current IK1. Objective: The purpose of this study was to determine quantitatively the relative current densities of If and IK1 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-ΔΔΔ with the S3-S4 linker residues EVY235-7 deleted to favor channel opening. Results: Whereas control atrial cardiomyocytes remained electrically quiescent and had no If, 18{\%} of Ad-CMV-GFP-IRES-HCN1-ΔΔΔ (Ad-CGI-HCN1-ΔΔΔ)-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 If at -140 mV (If,-140 mV = -9.32 ± 1.84 pA/pF). In the remaining quiescent Ad-CGI-HCN1-ΔΔΔ-transduced atrial cardiomyocytes, two distinct immediate phenotypes were observed: (1) 13{\%} had a hyperpolarized resting membrane potential (-56.7 ± 1.3 mV) with If,-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 If,-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 IK1 and If is necessary for induction of atrial automaticity. Conclusion: Optimized pacing induction and modulation can be better achieved by engineering the If/IK1 ratio rather than the individual currents.",
keywords = "Gene transfer, HCN channel, Pacemaker",
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T1 - Overexpression of HCN-encoded pacemaker current silences bioartificial pacemakers

AU - Lieu, Deborah

AU - Chan, Yau Chi

AU - Lau, Chu Pak

AU - Tse, Hung Fat

AU - Siu, Chung Wah

AU - Li, Ronald A.

PY - 2008/9

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N2 - 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 If or on minimizing its presumptive opponent, the inwardly rectifying potassium current IK1. Objective: The purpose of this study was to determine quantitatively the relative current densities of If and IK1 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-ΔΔΔ with the S3-S4 linker residues EVY235-7 deleted to favor channel opening. Results: Whereas control atrial cardiomyocytes remained electrically quiescent and had no If, 18% of Ad-CMV-GFP-IRES-HCN1-ΔΔΔ (Ad-CGI-HCN1-ΔΔΔ)-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 If at -140 mV (If,-140 mV = -9.32 ± 1.84 pA/pF). In the remaining quiescent Ad-CGI-HCN1-ΔΔΔ-transduced atrial cardiomyocytes, two distinct immediate phenotypes were observed: (1) 13% had a hyperpolarized resting membrane potential (-56.7 ± 1.3 mV) with If,-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 If,-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 IK1 and If is necessary for induction of atrial automaticity. Conclusion: Optimized pacing induction and modulation can be better achieved by engineering the If/IK1 ratio rather than the individual currents.

AB - 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 If or on minimizing its presumptive opponent, the inwardly rectifying potassium current IK1. Objective: The purpose of this study was to determine quantitatively the relative current densities of If and IK1 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-ΔΔΔ with the S3-S4 linker residues EVY235-7 deleted to favor channel opening. Results: Whereas control atrial cardiomyocytes remained electrically quiescent and had no If, 18% of Ad-CMV-GFP-IRES-HCN1-ΔΔΔ (Ad-CGI-HCN1-ΔΔΔ)-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 If at -140 mV (If,-140 mV = -9.32 ± 1.84 pA/pF). In the remaining quiescent Ad-CGI-HCN1-ΔΔΔ-transduced atrial cardiomyocytes, two distinct immediate phenotypes were observed: (1) 13% had a hyperpolarized resting membrane potential (-56.7 ± 1.3 mV) with If,-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 If,-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 IK1 and If is necessary for induction of atrial automaticity. Conclusion: Optimized pacing induction and modulation can be better achieved by engineering the If/IK1 ratio rather than the individual currents.

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