EFFECTS OF BENZYLTETRAHYDROPALMATINE ON THE RAPIDLYACTIVATING COMPONENT OF DELAYED RECTIFIER POTASSIUM CURRENT IN GUINEA PIG VENTRICULAR MYOCYTES

AIMTo investigate the effect of benzyltetrahydropalmatine (BTHP) on the rapidly activating component of delayed rectifier K⁺current (I_kr) in single guinea pig ventricular myocytes. METHODSWhole-cell patch clamp technique was used to record I_kr. RESULTS I_kr was blocked by 1～100 μmol·L^-1 BTHP in concentration-, voltage-, and specifically frequency-dependent fashion, with IC₅₀ of 13.5 μmol·L^-1 (95% confidence range: 11.2～15.8 μmol·L^-1). 30 μmol·L^-1 BTHP reduced I_kr and I_kr,tail by (31±4)% and (36±5)% (N=6, P<0.01), respectively. The time constant for deactivation (τ′) of the tail current was decreased by 30 μmol·L^-1 BTHP from (238±16) ms to (196±14) ms, while drug had no any effect on the time constant for activation (τ) of I_kr,tail. CONCLUSIONBTHP inhibited I_kr in a frequency-dependent fashion.