Contribution of the funny current to the fight-or-flight heart rate increase

Sinoatrial node myocytes are cardiac pacemaker cells that fire spontaneous action potentials (APs) to set heart rate. Sympathetic stimulation accelerates the AP firing rate to match heart rate to changing metabolic demands. The role of the funny current (If) in the generation of spontaneous sinoatrial APs and in their sympathetic response has been debated for decades. We used the AP-clamp technique to directly measure If during sinoatrial APs in the absence and presence of β-adrenergic receptor- (βAR-) stimulation.