Estimated effective time-averaged [Ca²⁺]_i determining InsP₃R channel gating activity, as sensed by cytoplasmic regulatory Ca²⁺-binding sites at various distances from the channel pore in various lum-out experiments. Pipette solution [Ca²⁺]_f ([Ca²⁺]_r→∞), perfusion solution [Ca²⁺]_f ([Ca²⁺]_ER), V_app, [InsP₃], and cytoplasmic Ca²⁺-buffering conditions used in each set of experiment are tabulated in each corresponding graph. A–F are related to experiments investigating the effect of Ca²⁺ flux mediated by the cytoplasmic inhibitory Ca²⁺-binding site(s), whereas G–K are related to experiments investigating the effect mediated by the cytoplasmic activating site(s). The effective [Ca²⁺]_i that produced the observed channel P_o are marked by dotted lines and tabulated (in red for inhibitory Ca²⁺ site and in blue for activating Ca²⁺ site). Black curves are effective [Ca²⁺]_i profiles derived from Ca²⁺ flux of magnitude = P_o i_Ca. The limits for the distances between the regulatory Ca²⁺-binding site and the channel pore derived from these [Ca²⁺]_i profiles are marked by black dotted lines and tabulated in black. Green curves in A–F are effective [Ca²⁺]_i profiles derived from Ca²⁺ flux of magnitude = i_Ca. The upper limits for the distances between the inhibitory Ca²⁺ site to the channel pore derived from these [Ca²⁺]_i profiles are marked by green dotted lines and tabulated in green.