Figure 6.

Computational simulations of IP₃ diffusion and Ca²⁺ puff occurrence in response to the localized photorelease of a non-metabolizable IP₃ analogue in an ellipsoidal 3D geometry, assuming an effective diffusion coefficient of IP₃ (D_I) of 100 μm²s⁻¹. The upper panel shows IP₃ distribution 2 s after the flash. Lower panels show time series of local Ca²⁺ concentrations at cluster sites (in a 1 fL volume) located at increasing distances from the flash. Simulation procedures are the same as for Fig. 4. The rate of localized IP₃ photorelease, θ, is taken equal to 2500 μMs⁻¹, which allows to obtain the same spatiotemporal profile of IP₃ increase as the 250 μMs⁻¹ value for the 2D case, because of changes in volume.