Figure 3. Pyramidal cell HCN channel activation.

(a) Steady-state HCN channel activation as a function of Ca²⁺ and V_memb. Vertical lines are levels by color in (b). (b) Ih_m voltage-dependence shifts right- and upward with increasing Ca²⁺. red: baseline at 100 nM; green: 2 μM; blue: 12 μM. Maximum steady-state activation is 2 because the second open state has twice the conductance of the first open state. At resting Ca²⁺ maximum steady state activation is 1.