Figure 6.

A conduction model for hSlo and hSlo-D292N channels. (A) State diagram for a cyclic four-state model illustrating the metastable states of pore occupancy. The selectivity filter contains five K⁺ binding sites; K⁺ ions are depicted as green spheres. (B) Schematic free energy landscape for both hSlo and hSlo-D292N channels in standard conditions (symmetric 120 mM K⁺, no surface charge, and zero potential) during one permeation cycle. The landscape illustrates the free energy of the entire system “pore + ions” in different state of occupancy. The minima (G_0–3) are to the energies of the metastable states S_0–3. The maxima (G_{01–12–23–03}) are the transition energies. Results of model fitting to experimental data are shown in C and D. (C) Experimental (symbols) and fitted (lines) single channel I–V curves for WT hSlo (red) and hSlo-D292N (blue) at indicated symmetrical [K⁺]. (D) Experimental (symbols) and fitted (lines) single channel chord conductance vs. [K⁺] for hSlo (red) and hSlo-D292N (blue). The insert shows the model parameters. α₀ is the preexponential factor; G_0–3 are the free energies of the states S_0–3; G_{01–12–23–03} are the transition state energies_; Δx _in and Δx _out, are the fractional voltage drops on internal and external ion entry, respectively; Δx _pore is fractional voltage drops between two K⁺ binding sites within the pore; σ_out and σ_in are the external and internal surface charge densities, respectively. f is the position of the transition barriers. See for detailed description of model parameters.