action potential upstroke

Propafenone (Propafenonum) is only found in individuals that have used or taken this drug. It is an antiarrhythmia agent that is particularly effective in ventricular arrhythmias. It also has weak beta-blocking activity. The drug is generally well tolerated. The electrophysiological effect of propafenone manifests itself in a reduction of upstroke velocity (Phase 0) of the monophasic action potential. In Purkinje fibers, and to a lesser extent myocardial fibers, propafenone reduces the fast inward current carried by sodium ions, which is responsible for the drugs antiarrhythmic actions. Diastolic excitability threshold is increased and effective refractory period prolonged. Propafenone reduces spontaneous automaticity and depresses triggered activity. At very high concentrations in vitro, propafenone can inhibit the slow inward current carried by calcium but this calcium antagonist effect probably does not contribute to antiarrhythmic efficacy.

Ro 22-9194 is a class I antiarrhythmic agent. Ro 22-9194 (>=10 μM) caused a concentration-dependent decrease in the maximum upstroke velocity and shortening of action potential duration in guinea-pig ventricular cells.