title: HCN4 provides a 'depolarization reserve' and is not required for heart rate acceleration in mice.
abstract: Cardiac pacemaking involves a variety of ion channels, but their relative importance is controversial and remains to be determined. Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels, which underlie the I(f) current of sinoatrial cells, are thought to be key players in cardiac automaticity. In addition, the increase in heart rate following beta-adrenergic stimulation has been attributed to the cAMP-mediated enhancement of HCN channel activity. We have now studied mice in which the predominant sinoatrial HCN channel isoform HCN4 was deleted in a temporally controlled manner. Here, we show that deletion of HCN4 in adult mice eliminates most of sinoatrial I(f) and results in a cardiac arrhythmia characterized by recurrent sinus pauses. However, the mutants show no impairment in heart rate acceleration during sympathetic stimulation. Our results reveal that unexpectedly the channel does not play a role for the increase of the heart rate; however, HCN4 is necessary for maintaining a stable cardiac rhythm, especially during the transition from stimulated to basal cardiac states.
authors.affiliation: Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Herrmann
authors.forename: Juliane
authors.initials: J
authors.lastname: Stieber
authors.forename: Georg
authors.initials: G
authors.lastname: Stöckl
authors.forename: Franz
authors.initials: F
authors.lastname: Hofmann
authors.forename: Andreas
authors.initials: A
authors.lastname: Ludwig
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000378:metabolism*; D005786:Gene Expression Regulation; D006339:Heart Rate; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D015640:Ion Channel Gating; D007473:Ion Channels / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009154:Mutation; D020033:Protein Isoforms; D012849:Sinoatrial Node / Q000378:metabolism / Q000473:pathology
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D020033:Protein Isoforms; D000242:Cyclic AMP; D007545:Isoproterenol