Bored by anatomy?
Try this.

• Learn faster
  and with more fun
• Ace your next exam
  with ease
• Get expert support
  from anatomy nerds

Trusted by 2,000,000+
students & professionals

Start Now

Sodium potassium pump (Na+/K+ ATPase)

Author: Kevin Kuschel MD

Last update: May 27th, 2023

Learn anatomy faster and
remember everything you learn

Start Now

The sodium-potassium pump (Na+/K+ pump) is a transmembrane protein that actively transports three ions of sodium (Na+) out of the cell and two ions of potassium (K+) into the cell, with the usage of cellular energy (ATP). The result of this is the net loss of sodium ions from the cell.

The function of sodium-potassium ATPase is to maintain the sodium and potassium concentration differences between the intracellular and extracellular spaces, pumping each of them against their concentration gradients. This ensures maintenance of negative membrane potential, making this pump essential for the proper functioning of the nerve cells and their ability to generate and transmit action potentials.

As the Na+/K+ pumps use ATP (adenosine triphosphate), their mechanism of transport is active transport.

Structure and mechanism

The sodium potassium pump consists of two subunits, a large alpha unit and a smaller beta unit. The alpha unit is responsible for the ions transport, as it features:

• Three binding sites for sodium ions (Na+) on the surface that faces the intracellular space
• Two binding sites for potassium ions (K+) on its extracellular surface
• A region near the sodium sites with the ability to dephosphorylate ATP molecules (i.e. ATP-ase).

Remember, dephosphorylation is the removal of a phosphate group from an organic compound. Hence, the result of the ATPase will be the removal of one phosphate group, which transforms the ATP molecule with three phosphate groups, into the ADP molecule (adenosine diphosphate) with two phosphate groups.

The mechanism of sodium-potassium pump is summarized in the following steps:

1. When three ions of sodium bind to their respective binding sites, the ATPase portion of the pump gets activated

Three ions of sodium bind to sodium potassium pump.

2. The ATPase then decomposes the ATP molecule (adenosine triphosphate) into ADP molecule (adenosine diphosphate), resulting in phosphorylation of the pump.

Phosphorylation of the pump.

3. Phosphorylation releases a significant amount of energy, which induces conformational change of the pump, which then releases three sodium ions into the extracellular space.

Already mastered the basic anatomy of the nervous system? Try your hand at these interactive quizzes and worksheets to see how your knowledge fares.

Sodium ions released into the extracellular space.

4. When the pump is phosphorylated, it has low affinity for sodium (hence, releases it), but it also has high affinity for potassium. Thus, two K+ ions from the ECF bind to their binding sites on the pump.

Potassium binds to its sites on the pump.

5. The attached K+ ions trigger dephosphorylation of the pump, which then reverts to its previous conformational state, releasing potassium into the cell.

As a result, the electrical and chemical gradients of these ions are created and maintained.

Functions

The most important function of the Na/K pump is to maintain the volume of cells. Without sodium potassium pumps, the cells would swell until they burst. The explanation for this lies in a simple physiological principle: “The water goes where the sodium goes”. The human cells contain a lot of proteins that cannot exit it. These proteins have an overall negative charge, attracting positive ions such as sodium and potassium into the cell. The movement of these ions, including sodium, into the cells results with water following them and entering the cells as well. If there weren’t for Na+/K+ pump, this process would run until the cell would burst. In human cells, whenever the cellular volume is increased, the sodium potassium pump is immediately activated, removing sodium, which is then followed by water proportionally leaving the cell as well.

If the cell is at such a loss of sodium that it needs more of it, it then opens the sodium channels in the membrane. Due to the existing concentration gradient of sodium (higher concentration outside of the cell), this ion then freely can enter the cell via this process of facilitated diffusion.

References

• Betts, J. G., Young, K. A., Wise, J. A., Johnson, E., Poe, B., & Kruse, D. H. (2022). Anatomy and Physiology (2nd ed.). OpenStax. https://openstax.org/details/books/anatomy-and-physiology-2e
• Hall, J. E., & Guyton, A. C. (2016). Guyton and Hall Textbook of Medical Physiology (13th ed.). Elsevier, Philadelphia PA