The position of arginine in TM5 plays a role in determining the current amplitudes of O1 and O2 states. (A) A representative recording of S307R/R303C/Cysless shows a slight and barely discernible difference between the O1 and O2 states. But the all-points histogram fails to distinguish these two states. (B) Clear resolution of the O1 and O2 states in F311R/R303C/Cysless in both the single-channel trace (left) and all-points histogram (right). (C) A representative recording of F310R/R303C/Cysless on the left shows clearly resolvable two open states reflected as two distinct peaks in the all-points histogram on the right. (D) Expanded opening bursts marked in C to show detailed transitions in a gating cycle. The burst marked c shows a prototypical gating topology of C→O1→O2→C.
