The rundown of TRPM2 currents in excised patches reflects a progressive decline in the number of active channels. (A) Macroscopic TRPM2 current (I; black trace) activated in an inside-out patch by exposure to 32 µM ADPR and 125 µM Ca²⁺ (bars). Red line is a single-exponential fit to the time course of current rundown, which was subtracted from the current trace to obtain the time course of gating noise (Î; blue trace). Vertical gray lines and colored bars identify consecutive time windows over which the mean of I and the variance of Î were calculated. (B) Plot of −σ²(Î)/i as a function of −m(I) (colored circles), calculated for the segments of time shown in A. The solid black line was obtained by linear regression through the data and corresponds to a P_o of 0.93. Gray shaded area identifies the region corresponding to P_o values >0.8. (C) Current from five TRPM2 channels recorded in the continuous presence of 398 µM Ca²⁺ plus 32 µM ADPR. Red arrows mark the time points of irreversible inactivation of the individual channels. Colored bars identify time windows with constant N (between two red arrows). (D) Stability plots of P_o, mean open time (m.o.t.), and mean closed time (m.c.t.) for the five individual time windows with constant N, identified by color coding in C. Values were obtained by the cycle-time method (see section 4 in the online supplemental material, available) and are not corrected for missed events because of the filter dead time. Pipette [Ca²⁺] was ∼4 µM in both A and C.