Simulated [Ca²⁺]_i profiles around an InsP₃R channel (cytoplasmic free [Ca²⁺] at various distances from the channel pore axis) under various Ca²⁺-buffering conditions. Buffering conditions are indicated for the profiles shown. [Ca²⁺]_ER = 300 µM. Bulk [Ca²⁺]_i (far from the channel) = 2 µM. (A) [Ca²⁺]_i profiles at different t after the channel opens, plotted in different colors as indicated. (B) The channel opened continuously for 50 ms before it closed. Profiles at different t after the channel closed are plotted in different colors as indicated. Even with the weakest buffering (0.1 mM HEDTA), [Ca²⁺]_i profiles reach steady-state level within 1 ms of the channel opening, and [Ca²⁺]_i around the channel returns within 100 µs to essentially the level that existed before the channel opened.