[
LABEL PHASES 3 AND 4 ON THE ACTION POTENTIAL WITH THE LABELS FOR PHASES 0, 1 AND 2 STILL PRESENT BUT DULLED] The accumulation of potassium ions in the extracellular space results in a rise in potassium conductance. This increase in potassium conductance, coupled with the high electrical driving force for potassium, results in the rapid efflux of potassium from the intracellular to the extracellular compartment (the rapid potassium outward current). This terminates the plateau and generates the phase of rapid repolarization (phase 3), bringing the transmembrane potential back to its resting level of approximately -85mV.