Block by bbTBA results in complex multicomponent relaxations. (A) Currents were activated with the indicated voltage protocol (top), with 10 µM Ca²⁺ in the presence of 75 µM bbTBA. Each trace is the average of 30 individual runs. Dotted red lines indicate the average current level at the end of each voltage step to highlight the marked undershoot that can occur after the initial rapid onset of block. (B) In a different patch, the same voltage protocol was used to activate BK currents either with 4 (top) or 300 µM Ca²⁺ (bottom), in both cases with 75 µM bbTBA. At 4 µM, dotted lines indicate steady-state current levels to highlight the undershoot after initial rapid block. With 300 µM Ca²⁺, no undershoot is observed.