Figure 4.

Proposed phylogenetic tree depicting the evolution of voltagedependent cation channels. Pore-forming unit isoforms representing each channel are shown in parentheses. (TM – Transmembrane domain; D – Domain; K_T – Two-pore domain K⁺ channel; K_IR – Inward rectifi er K⁺ channel; K_ATP – ATPsensitive K⁺ channel; HVA – High-voltage activated; LVA – Low-voltage activated; Kv – Voltage-gated K⁺ channel; K_QT – Long-QT K⁺ channel; Kca – Ca²⁺-activated K⁺ channel; SK – small-conductance Ca²⁺-activated K⁺ channel)