CaM (WT) can recover SK channel activity. (A) Representative current traces with a patch from a CaM (E2Q)–coinjected oocyte at the following time points: (1) immediately after patch excision; (2) after rundown stabilized; (3) 50 min after the application of 20 µM CaM (WT); (4) the application of solution containing 16 µM Ba²⁺; and (5) finally in Ca²⁺-free solution. (B) Average current level at −80 mV measured every 3 s with the patch shown in A during the course of rundown and recovery. Legends in this and later figures show the different solutions that the patch is subjected to. Solid line represents fit with a single-exponential time course (τ = 39.7 min). (C) With the same patch shown in A and B, after recovery of SK channel activity with CaM (WT), solutions containing different free Ca²⁺ concentrations were applied to the patch. Average current level at −80 mV was measured at each concentration, normalized to the maximal value, and plotted as a function of Ca²⁺ concentration. The dose–response relationship is fitted with the Hill equation: I/I_max = 1/(1+(EC₅₀/[ Ca²⁺])^h), yielding EC₅₀ = 0.94 µM and h = 2.6. (D) A representative time course of the average current level at −80 mV with a patch excised from an oocyte coinjected with RNA for SK channels and CaM (WT).