sodium/potassium pump

The sodium-potassium pump, also known as the Na,K-ATPase, a member of the P-type class of ATPases, is a critical protein found in the membranes of all animal cells. It functions in the active transport of sodium and potassium ions across the cell membrane against their concentration gradients. For each ATP the pump breaks down, two potassium ions are transported into the cell and three sodium ions out of the cell.

The sodium-potassium pump creates an electrochemical gradient across cell membranes. The electrical gradient, created by the outflow of more positive sodium ions than the inflow of positive potassium ions, resulting in a relatively negatively charged cytoplasm,is used in neurons and muscles to create the action potentials responsible for nervous system function and muscular contraction. The chemical gradient, which is created by the higher concentration of sodium ions in the extracellular space as opposed to the cytoplasm, results in the tendency of sodium ions to flow down their concentration gradient and back into the cytoplasm through other transmembrane proteins. Cells use the chemical gradient to transport essential nutrients such as glucose and amino acids into the cell in a process called secondary active transport.

The purpose of the sodium-potassium pump is to create a resting membrane potential.  The resting membrane potential is the electrical potential of a cell at rest.

Active transport is the process by which substances are moved through the cell membrane, against the concentration gradient.  This mans that unlike passive transport, active transport requires chemical energy from an outside source.  The source of this energy is usually provided by a molecule called adenosine triphosphate or ATP.  Active transport processes that use ATP are known as primary active transport while those that use an electrochemical potential difference for fuel are called secondary active transport.

One example of active transport can be seen in the cells movement of sodium and potassium across the cell membrane.  This requires the use of ATP and what's known as the sodium-potassium pump.

The pump keeps sodium concentration within the cell low and outside of the cell high while the opposite applies to concentrations of potassium.  This is accomplished by the pumping of sodium and potassium ions (charged particles) in opposite directions across the membrane.

The sodium-potassium pump has many uses in cell function. The most obvious is that it helps maintain the electrochemical gradient in the cell. It allows for maintenance of the membrane potential by keeping a higher concentration of potassium inside the cell than out side, while maintaining a higher concentration of sodium outside than in (also the membrane is virtually impermeable to chloride owing to the negative charge which the membrane produces). Also in terms of a chemical gradient the sodium-potassium pump allows absorptive cells to transport nutrients into the the cell via secondary active transport. For example, glucose is co-transported (aka symported) with sodium into the cell, this process actually uses no energy, even though glucose is transported against its concentration gradient, because sodium flows down its concentration gradient allow the glucose symporter to function. Without the sodium-potassium pump the transport of glucose would eventually cease because the sodium would eventually equalize in the cell. Also the sodium potassium pump functions in restoring a muscle or neuronal cell to normal levels of sodium and potassium after synaptic activity.

The main purpose of this pump is that it maintains the membrane potential. It does this by actively moving 3 – Na+ ions extracellularly, while transporting 2 – K+ into the cell.