What happens to potassium ions during phase 3 of action potential?

During phase 3 of the action potential, the primary event occurring is the repolarization of the cardiac cell membrane, which is largely mediated by the movement of potassium ions (K+) out of the cell. This phase’s main characteristic is a significant increase in the permeability of the cell membrane to potassium ions, primarily through the opening of voltage-gated potassium channels.

As potassium ions exit the cell, it leads to a decrease in the positive charge inside the cell, helping to restore the resting membrane potential. The efflux of K+ thus has the effect of driving the membrane potential back towards the negative resting level. This process is crucial for the heart's electrical cycle and ensures that the cells are prepared for the next action potential.

This increased movement of potassium ions therefore results in a higher concentration of potassium outside the cell relative to inside, reflecting the dynamic changes that occur during the repolarization phase of the action potential. Understanding this phase is critical for grasping the overall mechanics of cardiac action potentials and their impact on cardiac function.