Abstract: The effects of BTHP on Ca²⁺-independent action potential and the two components of delayed rectifier potassium currents were studied in guinea pig single ventricular myocytes by using whole cell patch clamp technique. BTHP 30 μmol·L ^{- 1} significantly prolonged APD90 from 143±16 ms to 184±21 ms (P<0.01, n = 5) without affecting either the RP or APA , and the APD prolonging effects of BTHP were independent of extracellular Ca²⁺. BTHP inhibited both Ikr (IC50 = 719μmol·L ^{- 1}) and Iks (IC50 = 2214 μmol·L ^{- 1}) in a concentration-dependent fashion. The results demon-strated that BTHP had no obvious selectivity for Ikr and Iks.

Key words: Benzyltetrahydropalmatine, Patch clamp technique, Delayed rectifier potassium channel, Ventricular myocytes