Kinetics of block onset is more reliably estimated by step changes in equilibration conditions while in the constant presence of paxilline rather than by wash-in of paxilline. (A) Onset of paxilline is compared at −80 mV and 300 µM Ca2+ for two situations: first, simple perfusion of 100 nM paxilline over the cytosolic face of the face, and second, a change in equilibration conditions from 80 to −80 mV. Voltage protocols in each case are shown schematically. Available BK current was monitored by a 2-ms step to 160 mV applied at 0.5 Hz. Symbols over the voltage steps for a particular protocol correspond to the particular symbols showing the onset of block as a function of elapsed time, with single-exponential time constants as given. (B) Estimates of time constants from individual patches for each method of assessing paxilline block are shown along with means and STD. Each method was evaluated with the same patches. An F-test provided an assessment of whether variance for each set of estimates was significantly different.
