SK channels recovered with CaM (T80D) have reduced apparent Ca²⁺ affinity. (A) Representative dose–response relationships for SK channels recovered with CaM (WT) (filled circles), CaM (T80A) (open squares), and CaM (T80D) (filled triangles). In all cases, patches were excised from oocytes coinjected with RNA for SK channels and CaM (E/Q). Currents were allowed to run down before the application of 20 µM of individual types of CaM. Dose–response relationships were measured in CaM-free solutions. Solid lines are fits with the Hill equation (WT, EC₅₀ = 0.97 µM and h = 3.8; T80A, EC₅₀ = 1.03 µM and h = 3.0; T80D, EC₅₀ = 1.82 µM and h = 3.4). (B) Representative dose–response relationships for SK channels coexpressed with CaM (WT) (filled circles), CaM (T80A) (open squares), or CaM (T80D) (filled triangles). Solid lines are fits with the Hill equation (WT, EC₅₀ = 1.03 µM and h = 3.7; T80A, EC₅₀ = 1.14 µM and h = 3.1; T80D, EC₅₀ = 1.93 µM and h = 3.3). (C) Average values for EC₅₀ from experiments as shown in A and B. Dose–response relationships were individually fitted for each experiment. Error bars represent standard deviation. Trial numbers are shown in the brackets on the top. Labeling is interpreted as the following: SK only-inj, oocytes were injected with SK RNA alone; WT-coinj, CaM (WT) RNA was coinjected with SK RNA; WT-rec, SK channels recovered by CaM (WT) in patches from oocytes coinjected with RNA for the SK channel and CaM (E/Q). The same applies for CaM (T80A) and (T80D). EC₅₀ values for T80D-rec and T80D-coinj are not significantly different from each other (P > 0.05; Student's t test), but significantly different from all other columns (P < 0.01), and are therefore labeled with stars. All other columns are not significantly different from each other (P > 0.05).