Electrophysiological effects of propafenone on fast response action potential of papillary muscle of guinea pig

The electrophysiological effects of propafenone on the guinea pig papillary muscle were studied in vitro by intracellular microelectrode. At therapeutic doses(1.4-4.2 microg/mL) propafenone had no effect on RP,Vmax and APA of the fast response action potentials were prolonged relatively. The inhibition of propafenone on Vmax showed frequency dependent and potential dependent effects. E0.5 was shifed from -68.0±3.0 Mv to -73.6±2.9 mV by propafenone 1.4 microg/mL. Propafenone 4.2 microg/mL decreased the excitability of the papillary muscle, the strength-duration curve was shifted upward. The decreases in Vmax and excitability resulted in the anti-arrhythmic effect.