Figure 2.

Schematic of the calcium model. Ca²⁺ fluxes are shown with solid black arrows. IP₃ and Ca²⁺ feedback on the IP₃R and IP₃ degradation are shown with dashed arrows. Agonist concentration stimulates IP₃ production via PLC. IP₃ then degrades by dephosphorylation at rate k_5p and phosphorylation at a Ca²⁺-dependent rate k_3K (grey arrows). Increases in Ca²⁺ and IP₃ concentration raise the open probability of the IP₃R, releasing Ca²⁺ from the ER.