Fig. 3.
Schematic representation of action potential of a ventricular myocyte. Rapid depolarization (phase 0) is caused by opening of the fast sodium channels resulting a transient increase inward sodium current (INa). Phase 1 characterizes an initial repolarization is a result of a short-lived, hyperpolarizing outward K+ current (IKto) caused by the opening of a special type of transient outward K+ channel (Kto). Phase 2 or the plateau phase/slow repolarization represents delay in the repolarization which caused by the inward calcium movement through long-lasting calcium channels (ICa L) that open up when the membrane potential depolarizes to about −40 mV. Phase 3 or fast repolarization occurs when rectifier potassium channels (IKr and IKs) open with simultaneous inactivation of the calcium channels. Phase 4 represents resting membrane potential.