Moricizine (Ethmozine) Can Break Electrical Coupling between Rat Right Atrial Working Cardiomyocytes In Vitro.

A previously popular antiarrhythmic drug moricizine (ethmozine) is known for its blocking action on the fast sodium channels in cardiomyocytes. Its effects were examined only in isolated cardiomyocytes or in vivo. Here, the effect of moricizine (10 μM) was examined in vitro on perfused right atrial preparation, where it completely reproduced all the previously observed phenomena and disturbed electrical coupling between the working cardiomyocytes in 35.3±3.4 min, which arrested generation of action potentials. During washing, the cardiomyocytes restored rhythmic firing in 34.1±3.7 min. Inhibition of firing in the working atrial cardiomyocytes was not accompanied by suppression of rhythmic activity in the pacemaker cells of sinoatrial node as attested by rhythmic miniature spikes in the records of resting (diastolic) potential of these cardiomyocytes. Thus, moricizine disturbed conduction between the working atrial cardiomyocytes without affecting the pacemaker activity.