A novel discovery of IK1 channel agonist: zacopride selectively enhances IK1 current and suppresses triggered arrhythmias in the rat.

Modulation of the inward rectifier K current (IK1) has profound effect on cardiac excitability and underlies new antiarrhythmic strategies. However, IK1-specific pharmacological tools, especially the selective IK1 agonists, are still lacking in the market. Zacopride, a gastrointestinal prokinetic drug, was found to be a selective IK1 channel agonist. By using the whole-cell patch clamp technique, it was found that zacopride (0.1-10 μmole/L) dose dependently enhanced the IK1 current in isolated rat cardiomyocytes, had no effects on other ion channels, transporters, or pumps. At the same dosage range, zacopride hyperpolarized the resting potential and shortened the action potential duration. When applied at the optimal dose of 1.0 μmole/L, zacopride could prevent or eliminate aconitine induced after depolarization and triggered activity in isolated cardiomyocytes. In a rat model of aconitine-induced arrhythmias both ex vivo and in vivo, zacopride (1.0 μmole/L or 25 μg/kg, respectively) treatment apparently protected the heart from ventricular tachyarrhythmias, which compares favorably with 7.5 mg/kg of lidocaine, a classical aconitine antidote. In conclusion, zacopride was found to be a selective IK1 agonist, and agonizing IK1 could prevent or eliminate aconitine-induced arrhythmias in the rat.