Figure 1.

Open-state block of BK channels by the BP in K⁺ solutions. (Top inset) 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: 0.4 nA, 50 msec. Zero-current level indicated by dashed line. (Main) Voltage dependence of BK channel activation (■) and fraction of channels not blocked by the BP (○) in 100 µM Ca²⁺. (Inset) Raw current recorded at + 60 mV from a holding potential of −80 mV in the absence (black) and presence (red) of 2 µM BP. Calibration: 2 nA, 50 msec. Zero-current level indicated by dashed line. (Boxed inset) Magnified view of the currents after repolarization to −80 mV, with the peak current in the BP scaled to match that of the control record. Calibration: 1 nA, 25 msec.