Figure 4.

Voltage dependence of the selectivity filter effective K⁺ equilibrium, K _eq, and the inner vestibule K⁺ site affinity, K _K. The K _eq (▪) and K _K (○) data were obtained as described in text. The lines are fits of Eq. 2 to the data. The electrical distance parameter, δ, for the selectivity filter equilibrium is 0.37, measured from the external side. The electrical distance for the vestibule site is 0.13 into the membrane electric field from the inner side, indicated by the minus sign. Other parameters from the fit are described in the text.