Schematic representation of the various chimeras. (A–C) Cartoon of hERG mutants. Details of these mutants can be found in Tristani-Firouzi et al. (2002). (D–I) Cartoon of HHHE-X chimeras adapted from Cowgill et al. (2019); Lin et al. (2024), where the VSD is from Mus musculus HCN1 (shown in red) and pore is from Homo sapiens EAG (shown in black), while the CTD is different in each chimera. (D) CTD from Mus musculus HCN1. (E) CTD from Mus musculus HCN2. (F) CTD from Strongylocentrotus purpuratus HCN. (G) CTD from Homo sapiens ERG. (H) CTD from Arabidopsis thaliana KAT1. (I) CTD from Arabidopsis thaliana AKT1.