Figure 8. Direct inhibition by halothane and isoflurane of Potassium(Calcium2+) channel activity. Single channel activity measured in the inside-out, patch-clamp configuration. The patch pipette was filled with a 200 mM KCl + 1 micro Meter free Calcium2+solution, and the bath was superfused with a 200 mM KCl solution containing 0.8 micro Meter free Calcium2+plus halothane or isoflurane at various concentrations. Single channel activity was measured in control conditions and 40 s after perfusing with the anesthetics. The applied potential was equal to 60 mV throughout. (A)(i) Effect of 2 mM halothane. In this example, halothane caused a 94% inhibition of the channel activity. (ii) Effect of 0.4 mM halothane. A 66% reduction in channel activity was observed in this case. (B)(i) Effect of 0.5 mM isoflurane. In this example, isoflurane caused a 83% inhibition of the open probability. (ii) Effect of 1 mM isoflurane. A 52% reduction in channel activity was observed in this case. The channel open probability was estimated from current amplitude histogram taken throughout 30-s periods. Arrows (c) point to zero current level of channel.