Objective: To study the effect of phenolic alkaloids of Menispermum dauricum (PAMD) on the action potential in papillary muscles of guinea pig and dominant pacemaker cells of rabbit sinoatrial nodes. Method: Capillary grass microelectrode was used to record the paction potential in papillary muscles of guinea pigs

study the effect of different concentrations (1

3

10 μmol·L-1) of PAMD on action potential duration (APD)

effective refractory period (ERP)

maximum upstroke velocity (Vmax)

amplitude (APA) and overshoot (OS). Capillary grass microelectrode was also used to record the paction potential in dominant pacemaker cells of rabbit sinoatrial nodes and study the effect of different concentrations (1

3

10 μmol·L-1) of PAMD on APD

maximal diastolic potential (MDP)

APA

Vmax

rate of pacemaker firing (RPF)

and velocity of diastolic (phase 4) depolarization (VDD). Result: According to the study for papillary muscle cells of right ventricular myocardia

PAMD can significantly prolong APD and ERP and delay Vmax in a concentration-dependent manner. PAMD also had a mild effect on the automatic rhythmicity of sinus nodes at concentration of 10 μmol·L-1

with a significant difference with the control group. Conclusion: PAMD have a stronger effect on ventricular muscles than sinoatrial nodes

suggesting that it has the potential to be prepared into an ideal drug for ventricular arrhythmia.