How does excess potassium outside of the cardiac cell affect the resting potential of the plasma membrane?

Excess potassium outside of cardiac cells influences the resting membrane potential by decreasing it. Under normal circumstances, the inside of a cardiac cell has a high concentration of potassium ions compared to the outside. This difference in concentration creates a negative resting membrane potential, which is primarily driven by the movement of potassium ions through ion channels in the membrane.

When there is an excess of potassium in the extracellular fluid, the concentration gradient for potassium decreases. As a result, the driving force for potassium to leave the cell diminishes. Since the resting potential becomes less negative when potassium accumulates outside the cell, the overall effect is a decrease in the membrane potential. This can lead to a condition known as depolarization, which can affect the excitability of cardiac cells and disrupt normal heart rhythms.