Chemistry and size of the selectivity filter of representative TRP channels and VGICs. TRP channel selectivity filters are diverse in both size and constituent residues. The diameters measured from two narrowest diagonally opposed oxygen atoms are shown at the top. The selectivity filters of Ca²⁺-selective Ca_vAb and K⁺-selective K_v2.1 are also shown for comparison. Ions in TRPV6 (Ba²⁺), Ca_vAb (Ca²⁺), and K_v2.1 (K⁺) are shown as purple spheres. PDB accession nos. are as follows: TRPV1-Apo (3J5P), TRPV1-DkTx (3J5R), TRPM4 (6BQR), TRPV4 (6BBJ), TRPV6 (5IWR), Ca_vAb (5KLB), and K_v2.1 (2R9R).