<P> Another important task of the Na - K pump is to provide a Na gradient that is used by certain carrier processes . In the gut, for example, sodium is transported out of the reabsorbing cell on the blood (interstitial fluid) side via the Na - K pump, whereas, on the reabsorbing (lumenal) side, the Na - glucose symporter uses the created Na gradient as a source of energy to import both Na and glucose, which is far more efficient than simple diffusion . Similar processes are located in the renal tubular system . </P> <P> Failure of the Na - K pumps can result in swelling of the cell . A cell's osmolarity is the sum of the concentrations of the various ion species and many proteins and other organic compounds inside the cell . When this is higher than the osmolarity outside of the cell, water flows into the cell through osmosis . This can cause the cell to swell up and lyse . The Na - K pump helps to maintain the right concentrations of ions . Furthermore, when the cell begins to swell, this automatically activates the Na - K pump . </P> <P> Within the last decade, many independent labs have demonstrated that, in addition to the classical ion transporting, this membrane protein can also relay extracellular ouabain - binding signalling into the cell through regulation of protein tyrosine phosphorylation . The downstream signals through ouabain - triggered protein phosphorylation events include activation of the mitogen - activated protein kinase (MAPK) signal cascades, mitochondrial reactive oxygen species (ROS) production, as well as activation of phospholipase C (PLC) and inositol triphosphate (IP3) receptor (IP3R) in different intracellular compartments . </P> <P> Protein - protein interactions play a very important role in Na - K pump - mediated signal transduction . For example, Na - K pump interacts directly with Src, a non-receptor tyrosine kinase, to form a signaling receptor complex . Src kinase is inhibited by Na - K pump, while, upon ouabain binding, the Src kinase domain will be released and then activated . Based on this scenario, NaKtide, a peptide Src inhibitor derived from Na - K pump, was developed as a functional ouabain - Na - K pump - mediated signal transduction . Na - K pump also interacts with ankyrin, IP3R, PI3K, PLC - gamma and cofilin . </P>

Sodium potassium pump is an example of antiport