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Fig. 3. Simulations of the effect of localized Ins(1,4,5)P₃ injections. Results have been obtained by integration of equations (1) to (5) with the ER density represented in Fig. 2 and the following parameter values: D_cyto=40 µm² second^-1, D_ER=4 µm² second^-1, D_IP=280 µm² second^-1, K_act=0.54 µM, K_inh (=(k_-/k₊)^1/ni) 0.28 µM, k_-=4 10^-3 second^-1, k₁=1.285 second^-1, b=2.5 10^-4 second^-1, K=1 µM, v_MP=1.2 µM second^-1, K_P=0.35 µM, V_PLC=0.015 µM second^-1, V_5P=0.67 µM second^-1, K_5P=8 µM, V_3K=3.35 10^-2 µM second^-1, K_3K=0.5 µM, K_A3K=0.3 µM, n_a=2, n_i=3. Most of these values come from previous modelling studies, where they were either taken from the literature or fitted to get agreement with the observations (Dupont and Erneux, 1997; Dupont et al., 2000). In the three simulations, during the flash time I_IP=7 µM second^-1 in the mesh points (46 to 54) along the X axis, and (89 to 97) along the Y axis (this region is indicated as a black square in the first panel). The resulting Ins(1,4,5)P₃ increase taken as an average on the whole egg ranges between 0.05 and 2.5 µM depending on the flash duration. Initial conditions are C_cyto=0.1 µM, C_lum=875 µM and the corresponding steady-state values of the other variables. To perform the simulations, mesh points are labelled 1 to 100 from left to right, and from top to bottom. To account for the circular shape of the egg (in two dimensions), the appropriate mesh points are excluded from the system. In this and all subsequent figures, the level of cytosolic Ca²⁺ is represented by the amount of Ca²⁺ bound to an indicator whose K_1/2 for Ca²⁺ is 0.7 µM. When representing the Ca²⁺ waves, the scale is different for each image, with red and blue representing the highest and the lowest instantaneous levels of cytosolic Ca²⁺, respectively.

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