Figure 2.

Voltage dependence of amitriptyline block on HERG current. (A) Current traces from a cell depolarized to −30 (left panel) and +30 mV (right panel) from the holding potential of −70 mV, before and after exposure to 5 μM amitriptyline. Tail currents were recorded at −60 mV. Magnitude of the decrease of the tail currents indicates that the block effect is larger at +30 mV. Calibration bars are 0.2 μA in height and 2 s in length. (B) Concentration-dependence of amitriptyline block at different membrane potentials. Conductance (G) in the presence of various concentration of amitriptyline was normalized to the maximum conductance (G_max) obtained in control, and plotted against amitriptyline concentrations. Data were from Figure 1C. Symbols with error bars represent mean±s.e.mean: each data obtained from seven cells. Lines are the fits of data to the Hill equation, giving IC₅₀ values of 23.0±3.24, 4.66±0.36 μM and Hill coefficients of 1.25±0.21, 1.23±0.11 at −30 and +30 mV, respectively.