Effects of butoprozine on ionic currents in frog atrial and ferret ventricular fibres. Comparison with amiodarone and verapamil.

The effects of butoprozine on cardiac membrane currents of frog atrial and ferret ventricular fibres were investigated in voltage clamp conditions by means of the double sucrose gap technique. Comparison was made with amiodarone and verapamil. Butoprozine was found to decrease the fast sodium and slow calcium inward currents and the delayed outward current in a dose-dependent manner. The reactivation kinetics of both inward currents were reduced by butoprozine. Amiodarone principally decreased the delayed outward current but high concentrations also depressed the inward currents. In the same way, small concentrations of verapamil inhibited the slow inward calcium current while high concentrations also affected the delayed outward and the fast inward sodium currents. The reactivation kinetics of both inward currents were reduced by amiodarone. These of the fast inward current remained unaffected by verapamil while these of the slow inward current were reduced or sometimes not appreciably changed. The effects of butoprozine on the ionic currents accounted for the modifications observed on the action potential and automaticity and this study allowed the understanding of the mechanisms by which the drug can exert its antiarrhythmic action. Some of them are common to amiodarone and verapamil.