The sodium-potassium pump is a carrier protein that actively transports sodium ions out of the cell and simultaneously transports potassium ions into the cell.The initial configuration of the carrier protein is such that binding sites on the inside of the cell are exposed and binding sites on the outside are inaccessible and there is no continuous passage from one side to another.Three sodium ions bind to receptor sites on the inside of the cell.ATP binds on the inside of the cell and is hydrolysed to release ADP. The configuration of the carrier protein changes, allowing the sodium ions to diffuse to the outside of the cell and exposing the potassium binding sites on the outside of the cell.Two potassium ions bind on the outside of the cell. The phosphate group is released changing the configuration back to the initial configuration and releasing the potassium ions inside the cell.