Hyperpolarization-activated cation currents: from molecules to physiological function

Annu Rev Physiol. 2003:65:453-80. doi: 10.1146/annurev.physiol.65.092101.142734. Epub 2002 Nov 19.


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.

Publication types

  • Review

MeSH terms

  • Animals
  • Biological Clocks / physiology
  • Cations / metabolism
  • Cyclic Nucleotide-Gated Cation Channels
  • Humans
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Ion Channels / chemistry*
  • Ion Channels / physiology*
  • Myocardium / metabolism
  • Nerve Tissue Proteins*
  • Neurons / metabolism
  • Potassium Channels


  • Cations
  • Cyclic Nucleotide-Gated Cation Channels
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Ion Channels
  • Nerve Tissue Proteins
  • Potassium Channels