Overexpression of HCN-encoded pacemaker current silences bioartificial pacemakers

Heart Rhythm. 2008 Sep;5(9):1310-7. doi: 10.1016/j.hrthm.2008.05.010. Epub 2008 May 15.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / drug effects
  • Animals
  • Atrial Function / physiology*
  • Cardiac Pacing, Artificial*
  • Cyclic Nucleotide-Gated Cation Channels / drug effects*
  • Gene Transfer Techniques
  • Guinea Pigs
  • Heart Atria / cytology
  • Heart Atria / innervation*
  • Heart Ventricles / cytology
  • Heart Ventricles / innervation*
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Membrane Potentials
  • Myocytes, Cardiac / physiology*
  • Pacemaker, Artificial
  • Potassium Channels / drug effects*
  • Tissue Engineering
  • Up-Regulation
  • Ventricular Function / physiology*

Substances

  • Cyclic Nucleotide-Gated Cation Channels
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Potassium Channels