Transient Depolarizations Induced by Acetylstrophanthidin in Specialized Tissue

Isolated preparations of atrial specialized conduction fibers ("plateau" fibers) qualitatively resembled ventricular Purkinje fibers (false tendons) in their response to acetylstrophanthidin. Acetylstrophanthidin in concentrations of 1-3 X 10~ g/ml caused coupled, frequency-dependent transient depolarizations (TDs) in both types of fiber. In free-running strands of plateau fibers the TDs could reach threshold and generate coupled action potentials, but TDs and automatic responses did not occur in ordinary atrial muscle fibers. TDs were suppressed by elevation of the external potassium concentration. Automatic activity and TDs in atrial plateau fibers were abolished by acetylcholine. Automatic activity was also sometimes suppressed in false tendons by acetylcholine, but TDs and related coupled responses were not influenced.