(A) Scheme of the chemical reactions that were implemented in the model to calulate the UV-illumination-evoked increase in the free Ca2+ concentration. The model considered Ca2+ (Ca) and Mg2+ (Mg) binding to the indicator dye (OGB-5N or Fluo-5F), to DM-nitrophen (DMn), and to buffers (ATP and/or an endogenous buffer). The forward (kon) and backward (koff) rate constants differ between chemical species. Upon photolysis, a fraction α of metal bound and free DMn made a transition to different photoproducts (PP1 and PP2; Faas et al., 2005). For model parameters see Table 2. (B) The scheme in (A) was converted to a system of differential equations and the time courses of the ‘real’ free Ca2+ (magenta) and the free Ca2+ reported by Ca2+ dye were simulated for the indicated uncaging fractions α. Note that after less than 1 ms the dye reliably reflects the time course of Ca2+. (C) Traces showing the steps used in the simulation of the kinetic model of release. (D) Graphical illustration of the three models used during the simulations. For model parameters see Table 3. (E) From left to right, predictions of each model and the experimental data for the inverse of (gray symbols, solid lines) and inverse of (black symbols, dashed lines), delay, vesicle replenishment rate between 10 and 100 ms, and the increase in the χ2 ratio for the single- compared to the bi-exponential fits. Red, yellow, and blue lines correspond to simulations of models 1, 2, and 3, respectively. For the χ2 ratio (right plot), the experimental data and the simulations are shown separately for 5-kHz- and 10-kHz-capacitance data (C5 and C10; black and brown, respectively) and the deconvolution data (D; green).