Figure 6.

State-independent block of BK channels by BP in Rb⁺ solutions. (A; insets) Time course of raw BK channel currents recorded in 100 µM Ca²⁺ in the absence (black) and presence (red) of 2 µM BP at the potentials indicated. Calibration: 0.1 nA, 50 msec. (Main) Steady-state current–voltage relation before (■), during (•), and after (□) application of 2 µM BP in Rb⁺ solutions. (B) Voltage dependence of BK channel activation (■) and fraction of channels not blocked by BP (○) in 100 µM Ca²⁺. (Inset) BK currents in response to repolarization to −80 mV from +40 mV in the absence (black) and presence (red; average of four records) of 2 µM BP, with the peak current in the BP scaled to match that of the control record. Calibration: 0.2 nA, 10 msec.