Figure 1.

Action potential (AP) genes and ion channels. The figure shows the summary of basic ion currents, genes and their targets in the AP. Various types of Ca²⁺ currents are shown, including L-type and T-type Ca²⁺ currents (CACNA1C, CACNA1H). KCND2-D3 genes (Kv4.2, Kv4.3), as voltage-gated fast transient outward potassium (I_to,f) and slow transient K⁺ outward (I_to,s) channels are also shown. Additionally, Na⁺ and K⁺ channels and their pore-regulated proteins and voltage regulations are also depicted. The Na⁺ current (SCN5A) is about 50 times lager as any other current during the depolarization phase (phase 1) of the AP, although its portion persists in the plateau phase. Several types of Ca^{2 +} currents e.g., CACNA1C (L-type) and CACNA1H (T-type), are activated during the phases 0, 1, and 2 of the AP. Fast transient outward potassium currents (KCND2-D3, encoding Kv4.2-Kv4.3) are functioning in the phases of 0, 1, and 2 of the AP. The activation of KCDN2 is rapidly terminated in the “notch” phase, phase 1, of the AP. Rectifier potassium channels include I_Ks (KCNQ1, KCNE1), I_Kr (KCNH2, hERG), and I_Kur (KCNA5), which are also activated in the phases of 0, 1, and 2 of the AP. Inward rectifier current (KCNJ2), pacemaker current (HCN4, I_f), and Na⁺–K⁺-ATPase (ATP1A/B) are activated in the phase 4 of the AP. Na⁺–Ca²⁺ exchange mechanism (NCX) is functioning in the phases of 1, 2, and 3 of the AP.