Effects of [Ca²⁺]_ER on InsP₃R-3 channel activity in various [InsP₃]. (A–C) Typical single-channel current traces from excised lum-out nuclear membrane patches recorded during a rapid switch of [Ca²⁺]_ER by perfusion solution exchange. For clarity, compositions of pipette solutions ([Ca²⁺]_i, concentration and nature of Ca²⁺ chelator used, [InsP₃]) common to all experiments presented in this figure (current traces and bar graphs) are tabulated at the top of the figure. Pipette solution composition(s) specific to each current trace is tabulated at the top of the corresponding current trace. In each current trace, V_app used is tabulated at left, color bars at the top indicate [Ca²⁺]_ER in the perfusion solutions, and blue bars at the bottom indicate segments used for evaluating the channel P_o tabulated below. In these figures, short current segments were plotted to show the InsP₃R channel gating more clearly. The mean P_o, t_o, and t_c ratios (discussed in Results and Discussion, and shown in bar graphs) were derived from current segments that are significantly longer to ensure that only single-channel nuclear patch current traces were used (see Materials and methods). (D–F) Bar graphs of mean ratios of channel P_o, t_o, and t_c, respectively, observed before and after [Ca²⁺]_ER switching between 70 nM and 300 µM for different [InsP₃]. Numbers beside the bars are the number of experiments (top) and perfusion solution switches (bottom) analyzed. ***, **, and * mark significant deviation of a ratio from unity (P < 0.005, 0.01, and 0.05, respectively; paired t test). These symbols and conventions are also used for Figs. 3–6, and 8 and 9. For clarity, bars of the same color in these figures correspond to the same set of data obtained under the same experimental conditions.