Representative I-V_app plots for single InsP₃R-3 channels in excised lum-out nuclear membrane patches under asymmetric ionic conditions used to determine channel permeability ratios for various ions. Compositions of pipette and perfusion solutions are described in Materials and methods. Selected data points for I_open and I_closed are plotted in green and pink, respectively. Red lines are linear fits to I_closed-V_app data points, and green ones are polynomial fits to I_open-V_app data points (linear for B; quadratic for A, E, and F; cubic for C and D). V_rev at the intersection of the I_open-V_app and I_closed-V_app fits are marked by dashed lines and tabulated. (A) Eight V_app ramps in one of four experiments to determine P_K:P_Cl. Junction potential corrected (V_junction) = −9.3 ± 0.4 mV. (B) 15 V_app ramps in one of three experiments to determine P_Na:P_K. V_junction = −1.5 ± 0.2 mV. (C) 10 V_app ramps in one of three experiments to determine P_Mg:P_K. V_junction = −0.7 ± 0.4 mV. (D) 43 V_app ramps in one of three experiments to determine P_Ca:P_K. V_junction = −1.4 ± 0.2 mV. (E) 35 V_app ramps in one of three experiments to determine P_Ba:P_K. V_junction = −2.6 ± 0.3 mV. (F) 16 V_app ramps in one of three experiments to determine P_Sr:P_K. V_junction = −2.2 ± 0.8 mV.