1.     Functions of Na-K pump

The sodium-potassium pump, also known as the Na+ -K+ ATPase, is a vital primary active transport carrier found in the plasma membrane of almost all cells in the human body. It utilizes the energy derived from the hydrolysis of adenosine triphosphate (ATP) to move ions against their respective electrochemical gradients.

The primary functions of the Na+-K+ pump include:

1. Maintenance of Ionic Gradients

The pump is directly responsible for creating and maintaining the steep concentration gradients for sodium and potassium across the cell membrane. It works by pumping three sodium (Na+) ions out of the cell and two potassium (K+) ions into the cell for every molecule of ATP hydrolyzed. This ensures that the intracellular environment remains high in K+ and low in Na+ relative to the extracellular fluid.

2. Regulation of Cell Volume

The Na+-K+ pump plays a critical role in controlling cell volume. Because cells contain fixed, negatively charged organic molecules that attract cations, they are prone to osmotic swelling. By constantly extruding Na+ ions, the pump effectively makes the membrane "functionally impermeable" to sodium, which opposes the osmotic forces and prevents the cell from swelling and bursting.

3. Electrogenic Contribution to Membrane Potential

Because the pump moves three positive charges out for every two it brings in, it creates a net outward current of positive charge. This makes the pump electrogenic, as it directly contributes to the negativity of the cell interior. While the majority of the resting membrane potential (RMP) is caused by ion diffusion, this electrogenic action typically adds about 3 to 10 mV to the total negative charge inside the cell.

4. Establishing the Resting Membrane Potential (RMP)

The pump provides the indirect energy source for the RMP by maintaining the high internal K+ concentration. This high concentration allows K+ to leak out of the cell through "leakage channels," which is the primary mechanism that generates the inside-negative RMP of approximately −70 to −90 mV.

5. Powering Secondary Active Transport

The steep Na+ gradient established by the pump serves as a "storage battery" of potential energy. This energy is used by various secondary active transporters to move other substances "uphill" against their own gradients. Examples include the cotransport of glucose and amino acids in the kidneys and intestines, and the counter-transport (exchange) of calcium (Ca2+) or hydrogen (H+) ions out of cells.

6. Supporting Excitability in Nerve and Muscle

By maintaining the necessary concentration gradients, the pump ensures that excitable cells are ready to produce electrical signals. Without the Na+-K+ pump, these gradients would eventually dissipate, and the cells would lose their ability to fire action potentials.

Clinical Significance

The function of this pump is so essential that in organs like the kidneys and brain, it accounts for 75% to 85% of total ATP consumption. Certain drugs, such as digitalis or ouabain (cardiac glycosides), specifically inhibit this pump to increase cardiac contractility by indirectly altering intracellular calcium levels