Fig. 5.
V404M does not alter apparent kinetics of pore opening. The kinetics of the pore-opening transition were estimated by a two-pulse protocol, in which the membrane was stepped twice from −100 to +60 mV separated by an interpulse interval of variable duration (Δt) (45). (A and B) Representative current traces recorded during the second pulse to +60 mV (black) are shown for (A) wild-type Kv4.2 and (B) V404M. Currents recorded after interpulse intervals of various durations have been superimposed. Note that V404M currents are shown on a compressed time base. Traces were fitted with a single exponential function (red) to estimate the time constant of activation (τact). (C) Values of τact for the wild type (■) and V404M (red ●) during the second pulse have been plotted vs. interpulse interval (Δt). Note the break in the timescale. Symbols at Δt = 0 ms indicate values of τact obtained during the first pulse (E). (D) Box plot shows the minimum values of τact (τact,min) from C obtained after the shortest interpulse interval for the wild type (black) and V404M (red). Mean values of τact,min ± SEM were the wild type (n = 11), 0.72 ± 0.06 ms and V404M (n = 20), 0.76 ± 0.09 ms. These values did not differ significantly. (E) The kinetics of opening in the wild type (■) and V404M (red ●) during the first pulse to +60 mV are compared. The discontinuous current traces reflect the experimental sampling rates. Data have been scaled to the same amplitude and overlaid. Single exponential fits to the data (solid curves) are superimposed (the wild type, black; V404M, red). WT, wild type.