<P> This was investigated by following the passage of radioactively labeled ions across the plasma membrane of certain cells . It was found that the concentrations of sodium and potassium ions on the two sides of the membrane are interdependent, suggesting that the same carrier transports both ions . It is now known that the carrier is an ATP - ase and that it pumps three sodium ions out of the cell for every two potassium ions pumped in . </P> <P> The sodium - potassium pump was discovered in the 1950s by a Danish scientist, Jens Christian Skou, who was awarded a Nobel Prize in 1997 . It marked an important step forward in the understanding of how ions get into and out of cells, and it has a particular significance for excitable cells such as nervous cells, which depend on this pump for responding to stimuli and transmitting impulses . </P> <P> The Na + / K + - ATPase helps maintain resting potential, effect transport, and regulate cellular volume . It also functions as a signal transducer / integrator to regulate MAPK pathway, ROS, as well as intracellular calcium . In most animal cells, the Na + / K + - ATPase is responsible for about 1 / 5 of the cell's energy expenditure . For neurons, the Na + / K + - ATPase can be responsible for up to 2 / 3 of the cell's energy expenditure . </P> <P> In order to maintain the cell membrane potential, cells keep a low concentration of sodium ions and high levels of potassium ions within the cell (intracellular). The sodium - potassium pump mechanism moves 3 sodium ions out and moves 2 potassium ions in, thus, in total, removing one positive charge carrier from the intracellular space . (Please see Mechanism for details). </P>

The na/k pump helps a muscle cell maintain a state of