Plasma membranes are semipermeable, allowing only selective molecules to pass through. The process of transporting potassium from inside to outside of plasmamembrane and sodium in the opposite direction is known as sodium potassium pump. This video describes structure and function of sodium potassium pump. Edited by Ashraf The sodium-potassium pump uses active transport, with energy supplied by ATP (adenosine triphosphate) molecules, to move 3 sodium ions to the outside of the cell for each 2 potassium ions that it moves in. One third of the body's energy expenditure is used in this process.