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

During phase 3 of the action potential, potassium ions play a crucial role in repolarization, which is the process that restores the cell's membrane potential back to a resting state after depolarization. In this phase, there is a significant increase in the permeability of the cell membrane to potassium ions due to the opening of voltage-gated potassium channels. As these channels open, potassium ions flow out of the cell, which results in an increase in the concentration of potassium ions outside the cell, as the intracellular concentration of potassium decreases.

This efflux of potassium ions is a critical step in the action potential as it helps to bring the membrane potential back towards the resting level, countering the earlier influx of sodium ions that caused depolarization. The movement and concentration change of potassium ions are essential for the proper timing and propagation of electrical impulses in cardiac tissues. Overall, during phase 3, the activity of potassium ions leads to a marked overall increase in extracellular potassium concentration, which is consistent with the physiology of cardiac myocytes during this critical phase.