HCN channels: new roles in sinoatrial node function

• HCN channels in the sinoatrial node are key regulators of the heart beat.
• HCN channels are also required for sinoatrial impulse propagation.
• HCN channels are involved in coordination and maintenance of sinoatrial network activity.
• HCN channels are crucial for stabilizing cardiac rhythmicity.

Hyperpolarization-activated cyclic nucleotide gated (HCN) channels pass a cationic current (Ih/If) that crucially contributes to the slow diastolic depolarization (SDD) of sinoatrial pacemaker cells and, hence, is a key determinant of cardiac automaticity and the generation of the heart beat. There is growing evidence, that HCN channel functions in the sinoatrial node (SAN) are not restricted to impulse formation but are also required for impulse propagation. In addition, HCN channels are involved in coordination and maintenance of sinoatrial network activity and, hence, are crucial for stabilizing cardiac rhythmicity. In the present review we will outline these new concepts.