The sodium-potassium pump is the transport protein that maintains the concentration gradient of these ions between the intra and the extracellular spaces. This protein is phosphorylated in each pumping cycle and then it pumps three sodium ions outside the cell and puts two potassium ions inwards. The phosphorylation is made by the binding of a phosphate donated by one ATP molecule that then is converted into ADP (adenosine diphosphate).

The job of the sodium-potassium pump, also known as sodium-potassium ATPase, is fundamental to keep the characteristic negative electric charge in the intracellular side of the membrane of the resting cell and to create adequate conditions of sodium and potassium concentrations inside and outside the cell to maintain the cellular metabolism.

Cell Membrane Review - Image Diversity: sodium-potassium pump