Linear relationship between mean of IPIs and , the reciprocal of the number of IP3R at a puff site. is chosen to be 3 ∼ 15, 20, and 25. For each value of , means of IPIs for two different [IP3]s, 0.1 μM and 0.2 μM, are computed and expressed as mean ± SE. For each [IP3], a least-square linear fitting is performed and plotted using a solid line. We set s−1.