Cardiac Pacemaker (If) Current: Physiological and Pharmacological Properties

Mammalian sinoatrial node (SAN) cells, the natural pacemaker cells of the heart, have an action potential characterized by the presence of a special phase, the slow diastolic (pacemaker) depolarization (phase 4), which drives pacemaker activity and has therefore attracted the interest of generations of cardiac physiologists. What is the basis of the pacemaker depolarization? Here the features of the “funny” (If) current of pacemaker cells and its involvement in the generation and autonomic regulation of heart rate are briefly addressed. There is also addressed the involvement of If in the pharmacological control of cardiac chronotropism, and how defective “funny” channels can be responsible for inherited heart rhythm disturbances.