| Sodium pump (Na, K-ATPase) is a membrane-bound protein that is present in the plasma membrane of all eukaryotic cells and belongs to a widely distributed class of P-type ATPase in cardiac myocytes. The Na+ enters and K+ leaves the cell by moving their electro-chemical gradients during each action potential. During the active transport process, the sodium pump helps restore these ion gradients by transporting three Na+ ions out of the cell and returning two K+ ions into the cell interior at the cost of one ATP molecule. Molecular studies have revealed that the pump is composed of oneα, oneβand oneγsubunits which combine to form the functional transporter. Theαsubunits carry out the ATPase activity and is responsible for binding ion transport. Four different isoforms ofαsubunit have been discovered, one of which, the alpha-1 (α1) isoform is expressed ubiquitously among tissues, whereas, the alpha-2 (α2) isoform has been identified principally in heart, muscle and brain tissue, the alpha-3 (α3) isoform has been identified primarily in neural tissues, and the alpha-4 (α4) isoform is a testis-specific isoform. Besides its tissue-specific distribution, theαsubunits possess species-specific distribution. For example,...
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