Supraventricular pacemaker activity in the canine heart: Contributions from HCN channels in control conditions and in a model of heart failure

See also article by Zicha et al.[1](the Nattel Research Group) (pages 472–481) in this issue. An interesting and clearly presented paper from the Nattel Research Group [1] in this volume of Cardiovascular Research provides new evidence for the expression of three isoforms of hyperpolarization-activated cyclic nucleotide-gated ion channels (HCN) in the sinoatrial node and atria of the adult canine heart. These measurements have been made under control conditions, and in the setting of a model of congestive heart failure–tachycardia-induced sinus node dysfunction. A major premise of this study is that although it is well-known that transmembrane ionic currents generated by HCN ion channels contribute to pacemaker activity, there appear to be significant species differences, and little information on this topic is available for the canine heart. The adult canine is a useful model for making control measurements and then studying selected pathophysiological paradigms which may be relevant to human clinical cardiac electrophysiology and to heart failure [2–5].