Figure 5.

(A) Effect of piceatannol on potassium channels of rat ventricular cells. Co²⁺ (1 mmol·L⁻¹) was always present in the bath to block I_Ca,L. The left top shows the typical current traces of transient outward currents (I_to) followed by a sustained outward currents and the inwardly rectifying potassium current (I_K1) in the absence and presence of piceatannol at 100 µmol·L⁻¹. The membrane potential was held at −80 mV, and was either depolarized to +60 mV to activate the transient outward currents or hyperpolarized to −140 mV to elicit I_K1 for 300 ms. The lower panael of (A) shows the I-V curves of the current density at peak (I_peak) and at the end of 300 ms (I_ss) in the absence and presence of piceatannol at the concentrations of 10, 30 and 100 µmol·L⁻¹. The outward currents were elicited by a family of depolarization steps from −60 mV to +60 mV increased by 10 mV every step, and a 20 ms depolarization pre-pulse was preceded to eliminate the contamination of sodium current. Data are shown in mean ± SEM (n= 6), and the asterisks indicate the statistical significance between the currents of control and drug-treated groups elicited at the same voltage level by one-way anova with Duncan's new multiple range test. The right top shows the dose-dependent inhibition of I_peak and I_ss by piceatannol. The curves are fitted by the Hill equation (1). (B) Effect of piceatannol on I_Kr in HEK293T cells transfected with hERG encoding the alpha-subunit of I_Kr. I_Kr was elicited by a family of depolarization steps increased every 20 mV for 300 ms from holding potential at −80 mV, and followed by the repolarization at −40 mV to record the tail currents. The right top of (B) plots the I-V curves constructed by the peak amplitude of the tail currents elicited at the respective depolarization steps. Data are shown in mean ± SEM (n= 6), and the asterisks indicate the statistical significance between the currents of control and drug-treated groups elicited at the same voltage level by one-way anova with Duncan's new multiple range test. The right bottom of (B) shows the dose-dependent inhibition of I_Kr,tail elicited at +60 mV by piceatannol. The curve is fitted with the Hill equation (1).