Strophanthidin (Strophanthidine) can induce calcium overload in vivo.

The effect of potassium and rubidium on the electrical and mechanical activity of canine Purkinje fibers were studied in vitro in the presence and absence of strophanthidin. METHODS AND RESULTS: High (5.4mM) K or 2.7 Rb decreased the force of contraction. In the presence of these ions, strophanthidin(Strophanthidine) increased the force of contraction as usual but the onset of arrhythmias was delayed. During the toxic stage of strophanthidin, high K or Rb increased the force of contraction, abolished the arrhythias and improved markedly the action potential. In the presence of calcium overload induced by exposure to a K-poor or Na-free solution, K and Rb induced an increase in force of contraction. And in ventricular muscle these ions relaxed the contracture induced by strophanthidin. CONCLUSIONS: It is concluded that K and Rb (in addition to other mechanisms) exert an antiarrhythmic action by increasing potassium conductance and by reducing the calcium overload induced by strophanthidin.