Fig. 11.

The average fractional activation of open BK channels after short depolarizations is higher than the average fractional activation of open BK channels after long depolarizations. A, BK current was elicited in a perforated patch-clamped cell with a step to −9 mV for 5 msec to produce Ca²⁺ influx and immediately followed by a step to +81 mV. The voltage protocol was repeated every 1.5 sec, and, immediately after the second episode, 50 μmmuscarine was applied. Shown here are the current traces immediately before and after the muscarine application. Instantaneous and peak current before muscarine application were 4355 and 5097 pA. Instantaneous and peak current after muscarine application were 4121 and 13232 pA. B, The Ca²⁺ influx step was increased to 50 msec in the same cell. As before, 50 μm muscarine was applied after the second episode. Shown here are the current traces immediately before and after muscarine application. Instantaneous and peak currents before muscarine application were 4414 and 7900 pA. Instantaneous and peak currents after muscarine application were 7119 and 12138 pA. Closedand open arrows indicate peak and instantaneous currents, respectively. Perforated-patch method.R_s, 14 MΩ;C_m, 6 pF; 80% compensated. Sampling period, 500 μsec.