Interaction of Pacemaker Cells and Fibroblasts in the SAN. Another Way of Setting the “Clocks”?

A crucial point in heart physiology is to understand the ability of certain heart cells to generate action potentials (AP) independently of an extracardiac stimulus, property known as automatism. Within these automatic cells, the pacemaker cells (PCs) of the sinoauricular node (SAN) are the primary determinants of the cardiac frequency.The most conspicuous characteristic of the AP of the PCs cells is the spontaneous diastolic depolarization (DD), which determines its automaticity and pacemaker activity. In fact, changes in the slope of this spontaneous DD have a major influence on the frequency of AP generation, ultimately establishing the heart rate.