Pore-lining residues dehydrate permeating Na ⁺ . (A) Frequency of pore-lining residues, which assist in Na⁺ dehydration as it permeates the channel. (B) Snapshot of neighboring residues D55 and N61 and partially dehydrated Na⁺ with five coordinating water molecules. (C) Snapshot of residue D55 on one monomer and T40 from the ECS1 of an adjacent monomer stabilizing a dehydrated Na⁺ with three coordinating water molecules.