Two main configurations for the aromatic rings of F339 and F340 residues. (A) A snapshot from simulation at 5 mM external K⁺ conditions showing the interaction of the F340 side-chain with V310, L273, and G269 residues of the same subunit at a dihedral angle of C-Cα-Cβ-Cγ ∼160^o. (B) Side chains of T311 of the same subunit and those of V334 and I337 of the neighboring subunit stabilize the aromatic ring of F340 after its flipping (dihedral angle of ∼55^o). (C) A snapshot from simulations at 5 mM external K⁺ showing the interaction of F339 with I268, T265, and G269 residues of the same subunit and with L251′ of the neighboring subunit. These interactions stabilize the benzene ring of F339 at C-Cα-Cβ-Cγ dihedral angle of ∼158^o. (D) Molecular interactions with the aliphatic side-chains of L251′, V255, and L347 when the benzene ring of F339 flips (dihedral angle of ∼158^o). (E) Mean amplitude histogram showing the distribution of the dihedral angle of the aromatic rings of F339 and F340 residues. The results of 10 simulations at 5 mM (open circles) and 150 mM K⁺_o conditions (filled circles) are shown. Colors of lines and symbols correspond to subunit positions as shown in the inset. Error bars in the graphs represent ± SEM.