Deep bradycardia and heart block caused by inducible cardiac-specific knockout of the pacemaker channel gene Hcn4

Proc Natl Acad Sci U S A. 2011 Jan 25;108(4):1705-10. doi: 10.1073/pnas.1010122108. Epub 2011 Jan 10.


Cardiac pacemaking generation and modulation rely on the coordinated activity of several processes. Although a wealth of evidence indicates a relevant role of the I(f) ("funny," or pacemaker) current, whose molecular constituents are the hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels and particularly HCN4, work with mice where Hcn genes were knocked out, or functionally modified, has challenged this view. However, no previous studies used a cardiac-specific promoter to induce HCN4 ablation in adult mice. We report here that, in an inducible and cardiac-specific HCN4 knockout (ciHCN4-KO) mouse model, ablation of HCN4 consistently leads to progressive development of severe bradycardia (∼50% reduction of original rate) and AV block, eventually leading to heart arrest and death in about 5 d. In vitro analysis of sinoatrial node (SAN) myocytes isolated from ciHCN4-KO mice at the mean time of death revealed a strong reduction of both the I(f) current (by ∼70%) and of the spontaneous rate (by ∼60%). In agreement with functional results, immunofluorescence and Western blot analysis showed reduced expression of HCN4 protein in SAN tissue and cells. In ciHCN4-KO animals, the residual I(f) was normally sensitive to β-adrenergic receptor (β-AR) modulation, and the permanence of rate response to β-AR stimulation was observed both in vivo and in vitro. Our data show that cardiac HCN4 channels are essential for normal heart impulse generation and conduction in adult mice and support the notion that dysfunctional HCN4 channels can be a direct cause of rhythm disorders. This work contributes to identifying the molecular mechanism responsible for cardiac pacemaking.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / drug effects
  • Animals
  • Blotting, Western
  • Bone Density Conservation Agents / pharmacology
  • Bradycardia / genetics
  • Bradycardia / physiopathology*
  • Cyclic Nucleotide-Gated Cation Channels / genetics
  • Cyclic Nucleotide-Gated Cation Channels / physiology*
  • Electrocardiography
  • Female
  • Fluorescent Antibody Technique
  • Heart / drug effects
  • Heart / physiopathology*
  • Heart Block / genetics
  • Heart Block / physiopathology*
  • Heart Rate / drug effects
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Male
  • Mice
  • Mice, 129 Strain
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Mice, Transgenic
  • Myocardium / metabolism
  • Myocytes, Cardiac / drug effects
  • Myocytes, Cardiac / metabolism
  • Myocytes, Cardiac / physiology
  • Receptors, Adrenergic, beta / metabolism
  • Sinoatrial Node / drug effects
  • Sinoatrial Node / metabolism
  • Sinoatrial Node / physiology
  • Tamoxifen / pharmacology


  • Bone Density Conservation Agents
  • Cyclic Nucleotide-Gated Cation Channels
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Receptors, Adrenergic, beta
  • Tamoxifen