The key difference between membrane potential and equilibrium potential is that membrane potential is the electrical potential difference between the outside and inside the plasma membrane of a cell while equilibrium potential is the membrane potential required to produce electrochemical equilibrium.
Different substances, especially ions and nutrients, go in and out of the cell via the cell membrane. In order to take ions and nutrients inside the cell, cells generate and maintain a membrane potential across the plasma membrane. The membrane potential is the difference of voltage or electric potential between the inside and the outside of the cell. It works as a force to facilitate the movement of ions passively in one direction. However, equilibrium potential restricts the ion movement across the membrane. It is the membrane potential at which the net flow is zero across the membrane. Therefore, at the equilibrium potential, ions do not move into or out of the cell.
CONTENTS
1. Overview and Key Difference
2. What is Membrane Potential
3. What is Equilibrium Potential
4. Similarities Between Membrane Potential and Equilibrium Potential
5. Side by Side Comparison – Membrane Potential vs Equilibrium Potential in Tabular Form
6. Summary
What is Membrane Potential?
Generally, there is a charge difference or voltage difference between inside and outside the cell membrane. Specifically, there is a negative voltage inside the cell while there is a positive voltage outside the cell. So, the membrane potential is the charge difference across the cell membrane. This occurs due to the separation of positive and negative ions across the membrane. In fact, the membrane potential is the force that facilitates the passive movement of ions in one direction. Under the resting condition, this voltage difference is known as the resting membrane potential. Upon stimulation, the charges across the membrane alter and create an action potential.
Figure 01: Membrane Potential
There are several factors that determine the membrane potential. They are ion concentrations inside and outside the cell, the permeability of the cell membrane to ions and the activity of ion channels such as Na+/K+-ATPase and Ca++ transport pumps located in the cell membrane.
What is Equilibrium Potential?
Equilibrium potential of an ion is the membrane potential that exactly balances the concentration gradient of the ion across the membrane. In other words, equilibrium potential is the membrane potential that is required to produce electrochemical equilibrium. At the equilibrium potential, the net flow of that particular ion across the membrane is zero. When considering K+ ion, the equilibrium potential of K+ is the negative charge across the membrane that is required to oppose the movement of K+ down its concentration gradient.
In glial cells, the resting membrane potential is equal to the equilibrium potential for K+ ion. Moreover, in neurons, the resting membrane potential is very close to the equilibrium potential of K+.
What are the Similarities Between Membrane Potential and Equilibrium Potential?
- Net electrochemical force is the difference between the membrane potential and the equilibrium potential.
- The membrane potential that is required to produce electrochemical equilibrium is the equilibrium potential.
What is the Difference Between Membrane Potential and Equilibrium Potential?
The membrane potential is the difference in total charge between the interior and exterior of the cell. In contrast, equilibrium potential is the membrane potential that exactly balances the concentration gradient of an ion across the membrane. So, this is the key difference between membrane potential and equilibrium potential.
Moreover, membrane potential forces ion movement passively in one direction, while equilibrium potential restricts the ion movements across the membrane.
Below is a summary of the difference between membrane potential and equilibrium potential.
Summary – Membrane Potential vs Equilibrium Potential
The membrane potential is the difference in electric potential between the interior and the exterior of a biological cell. On the other hand, equilibrium potential is the membrane potential required to produce the electrochemical equilibrium. At equilibrium potential, the net ion flow becomes zero. Therefore, there is no net flow of that particular ion from one side of the membrane to the other. Thus, this summarizes the difference between membrane potential and equilibrium potential.
Reference:
1. “Membrane Potential (Resting Membrane Potential) (Article) | Khan Academy”. Khan Academy, 2020, Available here.
2. “Reversal Potential”. En.Wikipedia.Org, 2020, Available here.
Image Courtesy:
1. “Basis of Membrane Potential2” By Synaptidude (CC BY 3.0) via Commons Wikimedia