Ajmaline (hydrochloride)

Ajmaline hydrochloride is a Class Ia antiarrhythmic agent. It inhibits HERG potassium channels with IC50s of 1.0 μmol/l and 42.3 μmol/l in HEK cells and moth spider oocytes respectively. The inhibitory effect of Ajmaline hydrochloride is rapid, reversible, and positive frequency dependent. It acts primarily on the open state of the HERG channel and may also be combined with the inactivated state. The inhibitory effect of ajmaline hydrochloride is dependent on aromatic residues in the S6 domain, and the sensitivity is significantly reduced in the inactivation-deficient HERG S620T channel. It can also slightly affect the activation voltage of HERG channels. Ajmaline hydrochloride's inhibitory effect on HERG channels may contribute to both its potent antiarrhythmic effects and its potential proarrhythmic risk.