Fig. 4.

(A) Protocol used to investigate I_hERG ‘availability’. From a − 80 mV, the membrane potential was stepped to +40 mV for 500 ms; this was then followed by 2 ms repolarization steps to potentials ranging from −140 mV to +50 mV, membrane potential was then stepped back to +40 mV for 100 ms (inset shows portion of protocol encompassing the transition to and from repolarizing steps). The amplitude of current transients elicited by the second step to +40 mV was used to assess I_hERG availability. (B) Representative traces in control. Selected traces are shown for clarity. Numbers indicate corresponding voltage of preceding 2 ms repolarization step. (C) Representative traces at 100 nM sarizotan. (D) Plots against voltage of normalized current transient amplitude in control and in 100 nM sarizotan (n = 7 cells); the inactivation V_0.5 and k values were derived from fits with standard Boltzmann function and are given in the Results text.