What is the equilibrium potential of a cell?

The equilibrium potential, also known as the reversal potential, is the electrical potential difference across a cell membrane that exactly balances the concentration gradient for a particular ion, preventing net movement of that ion across the membrane. For many cells, particularly neurons, the equilibrium potential for potassium ions (K+) is approximately -90 mV. This value is derived from the Nernst equation, which calculates the equilibrium potential based on the concentration gradient of the ion inside and outside the cell.

In the case of potassium, the concentration is typically higher inside the cell than outside. As a result, when the membrane is permeable to potassium, K+ ions will move out of the cell, causing the interior to become more negatively charged. At around -90 mV, the flow of potassium into the cell due to its concentration gradient is balanced by the flow out of the cell due to the electrical gradient, achieving equilibrium for potassium ions.

This value is significant in understanding neuronal action potentials and how neurons maintain resting membrane potential, thus highlighting the role potassium plays in excitability and signaling in the nervous system.

The other options do not represent the typical equilibrium potential for potassium or any standard ion involved in cellular physiology, making them less relevant in this context.