Figure 3.

State-independent block of BK channels by TBA 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 10 mM TBA at the potentials indicated. The voltage level before depolarization was −100 mV, and after the depolarization it was −80 mV (see Materials and methods). Calibration: 0.12 nA, 50 msec. Zero-current level indicated by dashed line. (Main) Steady-state current–voltage relation before (■), during (•), and after (□) the application of 10 mM TBA in Rb⁺ solutions. (B) Voltage dependence of BK channel activation (■) and fraction of channel not blocked by TBA (○) in 100 µM Ca²⁺.