Abstract

The action potential (AP) is a transient cell membrane depolarization emerging from the dynamic behavior of a diverse population of membrane ion channels. A prototypical ventricular myocyte AP, simulated with our human ventricular cell model (Grandi et al. 2010), is shown in Figure 39.1a and exhibits a steep upstroke, followed by a sustained slowly decaying plateau phase, which eventually gives way to rapid repolarization. Below the AP are shown the associated depolarizing currents, which are carried by inward Na⁺ and Ca²⁺ currents. Under physiological conditions, the Na⁺ current (I_Na) activates rapidly, producing the AP upstroke, and then inactivates nearly completely (Figure 39.1b). The L-type Ca²⁺ current (I_CaL) inactivates more slowly (Figure 39.1b), and less completely, allowing for the inward Ca²⁺ current to maintain the AP plateau phase.