Barium-induced automaticity in right ventricular muscle in the dog.

Pacemaker activity was induced in trabecular muscle fibers of canine hearts using oxygenated Tyrode solution with added barium chloride. Following exposure to barium (0.2 to 5 HIM) the resting potential decreased toward zero from 10 to 60%, depending on the concentration. Simultaneously, the duration of the action potential increased and early diastolic hyperpolarization appeared with diastolic depolarization characteristic of latent pacemaker activity. In concentrations above 0.75 mM, spontaneous activity appeared with presystolic upsweep at the threshold potential. The changes were reversible when normal Tyrode solution was readministered. Suppression of the induced pacemaker activity occurred on cooling or following imposed rapid stimulation. The changes produced by barium are consistent with a decrease in the conductance of the membrane for potassium. ADDITIONAL