Fig. 6.

A: the AP firing rate is broadly and smoothly modulated by P_up, yielding a unique parametric solution for the 3-Hz basal AP rate (black circle). B: interactions of Ca²⁺ and membrane clocks result in higher amplitude Ca²⁺ oscillations at higher P_up values. Since higher P_up values result in higher AP rates (A), the system clock operates following a Bowditch-like pattern: “the faster rate, the stronger release” (inset) thus overcoming a major functional limitation of the isolated SR Ca²⁺ clock (“the faster, the weaker” in Fig. 3).