Figure 4: Br-bTBA and bbTBA block closed MthK more slowly than TPeA.
From: Calcium ions open a selectivity filter gate during activation of the MthK potassium channel
(a) Relative Tl+ flux rates as a function of Br-bTBA and bbTBA (structures inset) incubation with closed MthK channels. Blocker equilibrations were fit to exponential functions, τBr-bTBA=9±3 s, τbbTBA=32±7 s (Equation 10, black and red solid lines, respectively). The fitted blocker time course for TPeA (from Fig. 3b) is shown for comparison (black dashed line). (b) Relative Tl+ flux rates versus incubation time with open MthK for 1 (black squares) and 3 μM (red circles) bbTBA. The results were simultaneously fit to equation (11) (lines; 
=2.1±0.2 μM, 
=17±2 μM−1 s−1). (c) Closed-state Br-bTBA dose–response curve for 45-s blocker incubations before activation of MthK by 17.2 mM Ca2+ (black squares). The results were fit to the Hill equation (red line; 
=2.5±0.2, nH=1.16±0.09). Dose response for open-state Br-bTBA block after the mixing dead time (grey circles). Grey line has no theoretical meaning. Symbols are the mean±s.d. from at least three (only two for bbTBA data in b) independent measurements.
