Table 3.

Energetic parameters for the HCN channel

Parameter	Parameter value
xm (V → −∞) (V = −160 mV)a	0.54 µM
xm (V → ∞) (V = −30 mV)a	1.72 µM
$-RT\hspace{0.17em}{N}_{\max }\hspace{0.17em}\ln \left(\frac{x_m{|}_{V\to \mathrm{\infty }}}{x_m{|}_{V\to -\mathrm{\infty }}}\right)+C_F$b	−3.0 kcal/mol
ΔGint (ligand pore)c	−2.2 kcal/mol

^aThe median ligand concentrations at very low and high voltages were approximated to the EC₅₀ values of the ligand binding curves reported in Kusch et al. (2010).

^bThe interaction energy between the ligand binding domain and the rest of the protein and C_F is the correction factor (Eq. 31). The following limiting values were used in calculating C_F: P_O(V_min, x_min) = 0.58; P_O(V_min, x_max) = 1; P_O(V_max, x_max) = P_O(V_max, x_min) = 0.

^cThe interaction between the ligand binding domains is the pore domain calculated from the HCN channel model parameters proposed in Kusch et al. (2012; equal to $-RT\hspace{0.17em}\ln (E_5/E_1)$; Fig. 4 A).