Fig. 3. Effects of protopanaxatriol (PPT) on IHERG, Itail, and Ideactivating-tail. (A) Representative current traces on human ether-a-go-go-related gene (HERG) K+ channel inhibitions by various concentrations of PPT. Currents were in response to 4-s voltage steps to 0 mV from a holding potential of –90 mV, followed by repolarization to –60 mV. IHERG was obtained at the end of depolarization; Itail was obtained at beginning of repolarization; slow Ideactivating-tail was obtained at the end of repolarization as indicated by the arrow. (B) Concentration-response curves for the inhibition of HERG K+ currents by PPT on IHERG, Itail, and Ideactivating-tail. Solid lines were fitted to the Hill equation. PPT was potent for the inhibition of Ideactivating-tail. Bars represent the means±SEM (n=5-7). (C) The representative control (upper traces) and 100 μM PPT-mediated currents (down traces) in I-V relationship. Currents were recorded at test potential from –60 to +50 mV. Itail and Ideactivating-tail were recorded after repolarization to –60 mV. (D) I-V relationships for HERG K+ currents measurement at the end of the 4-s test pulse before and after application of 3, 10, and 30 μM PPT (n=5). Currents were normalized to the control current at 0 mV for each oocyte. Data are represented by the means±SEM (n=7). (E) Effects of PPT on the steady-state activation curve for HERG K+ channel. Itail were normalized to the peak current under each condition, and the data were fitted with a Boltzmann function. Treatment of PPT (3, 10, and 30 μM) did not cause a leftward shift. Con, control.
