Effects of benzyltetrahydropalmatine on delayed after depolarization and triggered activity and rabbit His-bundle electrogram

Standard microelectrode techniques were used to study the effects of benzyltetrahydropalmatine (BTHP) on ouabain-induced delayed after depolarization (DAD) and triggered activity in isolated guinea pig papillary muscles. The results indicate that ouabain-induced DAD and triggered activity were abolished by BTHP 100 mumols/L. In anesthetized rabbit ECG heart rates were reduced in a dose-dependent manner from its control value of 288 +/- 14 to 261 +/- 14 (5 mg/kg) and 226 +/- 36 bpm (BTHP 10 mg/kg). P-R interval was prolonged. In His-bundle electrogram, H-V interval and V duration were not affected, but A-H interval was prolonged from 41 +/- 3 to 45 +/- 5 ms.