Depolarizing electrical current is also capable of inducing spontaneous pacemaker activity. That is illustrated in this figure, adapted from the work of Trautwein and Kassebaum (J. Gen. Physiol. 45:317,1961). The application of DC current for several seconds to a quiescent Purkinje fiber causes an action potential followed by diastolic depolarization. When the current strength is 0.4 uA (upper panel), the spontaneous diastolic depolarization that follows the action potential does not reach the threshold potential and the fiber does not generated spontaneous action potentials. When the current strength is increased to 1.0 uA (lower panel), the diastolic depolarization does reach threshold and spontaneous action potentials are generated until the current is discontinued. This suggests a possible mechanism by which currents of injury generated across ischemic boundaries might cause ectopic beats and rhythms.