Paxilline inhibition is faster at higher closed-channel probabilities. (A) All traces were obtained from the same patch with the indicated voltage protocol while in the continuous presence of 100 nM paxilline and 300 µM Ca²⁺. Black traces correspond to currents activated after a re-equilibration period at 80 mV (with 300 µM Ca²⁺), whereas red traces are the final trace after a change to a new equilibration voltage (as indicated). (B) The onset of current inhibition from the examples in A is plotted as a function of time at the new equilibration potentials. Red lines are single-exponential fits to the onset of inhibition. (C) Onset of inhibition at intermediate Pc is better fit with two (blue) exponential components than one (red). (D) The rate of block (means, SEMs, and individual estimates) from experiments as in B is plotted as a function of Pc, with Pc calculated from the G-V curves at 300 µM Ca²⁺. Closed red symbols correspond to the faster rate resulting from the fit of either one or two exponential components to the onset time course in B and C. (E and F) Onset of inhibition at −80 mV (E) and −100 mV (F) is shown for different paxilline concentrations along with single-exponential fits. (G) Blocking rate is plotted as a function of [paxilline]. The fitted red line has a slope of 2.1 × 10⁶ M⁻¹s⁻¹. Each dotted line connects determinations at different [paxilline] for single patches.