NaKATPase

To maintain the cell potential, cells need to keep a low intracellular (within) concentration of sodium ions, and high levels of potassium ions. Outside cells, there is high concentrations of sodium and low concentrations of potassium, so diffusion occurs through ion channels in the cell membrane. To keep the appropriate concentrations the sodium-potassium pump pumps sodium out and potassium in. The mechanism is:

• The pump, with bound ATP, binds 3 intracellular Na+ ions.
• ATP is hydrolyzed, leading to phosphorylation of a pump and release of ADP.
• A conformational change in the pump exposes the Na+ ions to the outside. The phosphorylated form of the pump has a low affinity for sodium ions and they are released.
• The pump binds 2 extracellular K+ ions, leading to the dephosphorylation of the pump.
• ATP binds and the pump reorients to release potassium ions inside the cell and the pump is ready to go again.

Oubain inhibits pump operation.

The electrical and concentration gradient established by the sodium-potasium ATPase supports not only the cell resting potential but theaction potentials of nerves and muscles. Export of sodium from the cell provides the driving force for several facilitated transporters, which import glucose, amino acids and other nutrients into the cell. Translocation of sodium from one side of an epithelium to the other side creates an osmostic gradient that drives the absorption of water.

See also: active transport