Discrete-State Stochastic Models of Calcium-Regulated Calcium Influx and Subspace Dynamics Are Not Well-Approximated by ODEs That Neglect Concentration Fluctuations

Figure 2

Steady-state probability distribution of the number of calcium ions (C, left column) and subspace calcium concentration (C, right column) for subspace volume of 𝑣₀=10⁻¹⁷ liters and subspaces that are 3 and 10 times larger. Parameters: 𝛼=0.049 μM/ms, 𝛽=0.01 ms⁻¹, 𝑐_∞=0.1 μM; the steady-state expected subspace calcium concentration is E[C]=𝑐_∗=5 μM.