Quinidine

Quinidine is a class I antiarrhythmic agent. Like all other class I antiarrhythmic agents, quinidine primarily works by blocking the fast inward sodium current (INa) which causes the phase 0 depolarization of the cardiac action potential to decrease (decreased Vmax). Quinidine also blocks the slowly inactivating, tetrodotoxin-sensitive Na current, the slow inward calcium current (ICa), the rapid (IKr) and slow (IKs) components of the delayed potassium rectifier current, the inward potassium rectifier current (IKI), the ATP-sensitive potassium channel (IKATP) and Ito. At micromolar concentrations, quinidine inhibits Na /K -ATPase by binding to the same receptor sites as the digitalis glycosides such as ouabain.