Figure 1.

Major ion channels underlying the action potential from different regions of the cardiac conduction system. (A) Schematic of major ion channels and representative action potentials from (A,B) sinoatrial node and (C,D) ventricular myocytes. Channels are color coded to correspond to phase of the AP where they make an important contribution. Abbreviations are as follows: Acetylcholine-activated K⁺ current (I_KAch); Inward rectifier K⁺ current (I_K1); L-type Ca²⁺ current (I_Ca); Na⁺/Ca²⁺ exchanger (I_NaCa); Na⁺/K⁺ ATPase (I_NaK); plateau K⁺ current (I_Kp); rapid (I_Kr) and slow (I_Ks) delayed rectifier K⁺ currents; sarcoplasmic reticulum (SR); SR Ca²⁺ release channel (RyR2); SR Ca²⁺ ATPase (SERCA); transient outward K⁺ current (I_to); TWIK-related K⁺ channel 1 current (I_trek); T-type Ca²⁺ current (I_Ca,T); voltage-gated Na⁺ current (I_Na).