Nifekalant

Nifekalant (MS-551), a class III antiarrhythmic agent, is a IKr potassium channel blocker with an IC₅₀ of 10 μM. Nifekalant can be used for refractory ventricular tachyarrhythmias research^[1][2]. In Vitro:Nifekalant interacts with the cardiac M2 and the peripheral M3 receptors with a K_i value of 27 and 74 mM, respectively. Nifekalant dose dependently blocks HERG channels with an IC₅₀ value of 7.9 mM, but Nifekalant does not block minK currents in the Xenopus oocyte expression system. Nifekalant blocks HERG channels mainly in their open state in a frequency dependent manner. As a pure K⁺ channel blocker, Nifekalant does not have negative inotropic effects which amiodarone has via a β-blocking action and does not affect cardiac conduction^[2]. In Vivo:In rats (a species deficient in functional cardiac IK), before coronary ligation, 3 mg/kg and 10 mg/kg MS-551 decreased the heart rate by 6% and 12%, and increased mean arterial pressure (MAP) by 14% and 33%, respectively. MS-551 prolongs the QT interval and reduced the incidence of sustained ventricular fibrillation (VF) after reperfusion^[3].