Gating kinetics manifest in rapidly perfused outside-out macropatches. (A, left) Mean I_PB responses from rapidly perfused outside-out cell-free macropatches triggered by PB applications (4 s) over a range of concentrations (μM) as indicated normalized to peak of a 500-μM response (means ± SEM; n = 3–5). Representative liquid junction potential response indicating the time of PB application (upward deflection). The application period was >30 s. (Right) Concentration–response relationships for macropatch I_PB peak, plateau, and tail amplitudes in the format used in Fig. 1 B. Smooth curve is the best fit of a logistic equation to tail current response (A = 8.1, x₀ = 1,100 μM, slope = 2.23; See Materials and methods). Whole cell tail current relationship (WC tail) reproduced from Fig. 1 B for comparison. Fraction of channels blocked at pulse end (fraction blocked) was calculated using I_PB, plateau, and tail amplitudes in the expression [(tail-plateau)/(tail)]. Fraction blocked approximates the conditional probability (P) of the block (B), given that it is either B or open (O) and is represented by the expression [ P{B | B or O} ] (see Results). The best fit of a logistic equation to fraction-blocked response (A = 0.97, x₀ = 620 μM, slope = 3.51) is not depicted. (B) Tail currents (means ± SEM) replotted from A on an expanded time scale at the indicated concentrations (μM). (Inset, left) Tail currents normalized by peak amplitude and time shifted to align current peaks to provide a comparison of deactivation time course. (Inset, right) 5,000-μM response replotted on semi-logarithmic axes showing that the time course is accounted for by a biexponential function that appears as linear phases (marked by straight lines), with associated fast and slow time constants (fast, τ_F; slow, τ_S).