What are the factors causing resting membrane potential of the cell?

The resting membrane potential is the steady electrical charge difference that exists across the plasma membrane of a cell when the cell is not actively sending any signal. In this state, the inside of the cell is negatively charged compared to the outside. The resting membrane potential is very important because it keeps the cell ready to respond quickly when it needs to perform actions like muscle contraction, nerve signal transmission, or other cellular activities. This electrical potential does not happen by chance but is the result of the combined action of several specific factors that maintain ionic gradients and regulate charge separation across the membrane.

Here are the main factors responsible for creating and maintaining the resting membrane potential.

1. Unequal Distribution of Ions Across the Cell Membrane

The first important factor is the unequal distribution of ions like potassium (K⁺), sodium (Na⁺), chloride (Cl⁻) and calcium (Ca²⁺) across the membrane. Potassium ions are found in high concentration inside the cell, while sodium ions are in high concentration outside the cell. This difference in concentration of ions across the membrane forms a chemical gradient, which is necessary for creating the resting membrane potential.

2. Selective Permeability of the Plasma Membrane

The plasma membrane does not allow all ions to pass equally. It is much more permeable to potassium ions than to sodium or other ions. Because of this selective permeability, more potassium ions tend to move out of the cell than sodium ions move inside. This movement of positive charges out of the cell makes the inside of the cell relatively more negative.

3. Sodium-Potassium Pump (Na⁺/K⁺-ATPase)

Another key factor is the sodium-potassium pump. This pump uses energy from ATP to move three sodium ions out of the cell and two potassium ions into the cell. As a result, more positive charges are removed from the cell than are brought in, helping to maintain a negative charge inside the cell at rest.

4. Presence of Negatively Charged Proteins and Organic Anions Inside the Cell

Inside the cell, there are many large proteins and organic molecules that carry a negative charge. These molecules cannot cross the membrane easily and remain inside the cell. Their negative charges add to the negativity of the intracellular environment and support the formation of the resting membrane potential.

5. Potassium Leak Channels

Potassium leak channels are special protein channels that allow potassium ions to slowly move out of the cell, even when the cell is at rest. As potassium leaves the cell, it carries positive charge out, making the inside of the cell even more negative compared to the outside. This continuous potassium leakage is a very important factor for maintaining the resting membrane potential.