β1 alters the affinity of the RCK1 site at constant voltage. (A and B) Outward K⁺ currents recorded at 0 mV and filtered at 2 kHz from macropatches containing ΔEΔB channels (A) or ΔEΔB + β1 channels (B) exposed to the indicated [Ca²⁺]. These currents demonstrate that Popen increases in a Ca²⁺-dependent manner when voltage is constant. A comparison of the dose–response relation for the effect of Ca²⁺ on Popen at 0 mV in the absence or presence of β1 is shown in C as the ratio NPopen to NPopen_min versus [Ca²⁺] and in D as Popen versus [Ca²⁺]. Each point represents the average of between 5 and 22 patches at each [Ca²⁺] tested. Error bars represent SEM.