Fig. 8.

Two-site/three-barrier Eyring model for permeation and block by Fe²⁺. A, energy levels and electrical distances for barriers and wells for Ca²⁺ and Fe²⁺. Energy levels (outside to inside) were 9.32, −12.73, 5.26, −6.97, and 15.65 RT. The electrical distances and energy profiles for Na⁺, Mg²⁺, and Ba²⁺ are from the report by Lopin et al. (2010). B to D, fits of the model to experimental II-V data are shown for permeation (B), block of the current carried by 2 mM Ca²⁺ (C), and block with 2 mM Ba²⁺ (D). E, calculation of the rate of Fe²⁺ entry with the indicated extracellular Fe²⁺ concentrations, in the presence of 2 mM extracellular Ca²⁺, for a single open channel. F, calculation of the steady-state rate of Fe²⁺ entry by considering channel gating (activation and inactivation). The steady-state open probability-voltage relationship calculated with the model described by Serrano et al. (1999) was convolved with the curves in E.