Moving sodium and potassium ions actively transported across the cell membrane against the concentration gradient. An active transport process involves expense of energy. The energy comes by hydrolysis of ATP. It involves an enzyme called Na+/K+-ATPase. This process is responsible for maintaining the excess of Na+ outside the cell as well as the excess of K+ ions on the inside. There is transport of three Na+ to the outside of the cell and the transport of two K+ ions to the inside. This unbalanced charge transfer contributes to the separation of charge across the membrane. The sodium-potassium pump is an important for action potential.