[NOTE: THE CALIBRATION.IN THE UPPER LEFT OF THE FIGURE IS INCORRECT AND SHOULD BE 50 (NOT 500)mv)]
This figure illustrates the ability of a decrease in extracellular potassium to increase the rate of spontaneous diastolic depolarization in the right bundle branch of the pig heart. When extracellular potassium is 4.8 mM (upper panel), there is only a slight degree of diastolic depolarization and the fiber is driven by an externally applied electrical stimulus. Fifteen minutes after decreasing extracellular potassium to 0.8mM (middle panel), there is an increase in the rate of diastolic depolarization but the fiber is still being externally driven. After 18 minutes (lower panel), the cell has developed true pacemaker characteristics and is now spontaneously active. This illustrates one mechanism by which hypopotassemia may be arrhythmogenic.