Effects of propafenone on slow response action potential and slow inward current of myocardium

The effects of propafenone on the slow response action potentials of guinea pig ventricular papillary muscles and the slow inward currents of canine Purkinje fibres were studied with intracellular microelectrodes and voltage clamp techniques. Propafenone 1.4 microg/mL decreased Vmax and APD to 71% and 87% of the control values, respectively. The ERP was prolonged to 115% and RP was not influenced. The inhibition of Vmax showed frequency-dependent manner. Propafenone 2.8 microg/mL decreased the excitability of the papillary muscles and decreased the slow inward currents of the Purkinje fibers from a peak value of 14+/-8 to 3.4+/-3.9 nA. It indicated that propafenone has a direct inhibitory effect on the slow inward currents.