[Pharmacologic effects of mansonine on arrhythmias induced in isolated rat heart].

The effect of 3 x 10(-13) M Mansonine (MSN) was observed on arrythmias induced on isolated rat heart, perfused with either hypopotassic solution, atropine solution, or MacEwen physiological saline at 18 degrees C. Generally the reversal of induced arrythmias was complete with the hypopotassic solution, and partial with the MacEwen solution at 18 degrees C. On the other hand, when atropine and MSN were combined, their effects induced heart arrest, probably due to an intracellular calcium accumulation. In this case, the heart recovery occurred by preventing the calcium influx, either through EDTA chelation, or blockade of calcium channels. It was concluded that MSN probably acts like most cardiac glycosides, by blocking the Na(+)-K+ ATPase. This may activate a calcium influx, which causes the subsequent positive inotropic effect, as well as a negative chronotropic effect due to an increase of the membrane activation set point.