Figure 4. Simulation of cytosolic Ca²⁺ oscillations in a pancreatic acinar cell during gradual store depletion when two subtypes of IP₃R are present.

The store was depleted gradually in the same way as in Figure 2. (A) [Ca²⁺]_c (lower trace) and [Ca²⁺]_ER (upper trace) in the whole-cell model with two subtypes of IP₃R. In this simulation, it was assumed that the ‘high-affinity’ IP₃R subtype had three times higher affinity to cytosolic Ca²⁺ than the subtype used for the simulation in Figure 2. (B) The rise time (•) and the decay time (○) of Ca²⁺ spikes during the simulation. (C) Bifurcation diagrams of [Ca²⁺]_c against [IP₃] in the whole-cell model. Steady-state solutions (solid line), the maxima and the minima of periodic orbits (broken line) are shown. S=200 μM in control and S=160 μM in depleted store.