The sodium pump is the principal means of active ion transport at the cell surface of most cell types. The minimum functional unit of the pump consists of the catalytic alpha subunit (mainly alpha1 and alpha2 in the heart), and a beta subunit (mainly beta1 in the heart) which is required for trafficking to the cell surface. Tissue-specific regulation of pump activity is achieved by expression of a third accessory subunit termed FXYD after a conserved extracellular motif.
In the heart, FXYD1 (phospholemman, UniProtKB - O00168 (PLM_HUMAN)) regulates the pump by modifying its Na affinity and Vmax. Unphosphorylated phospholemman inhibits the pump, and phosphorylation by PKA or PKC relieves this inhibition. Phospholemman is phosphorylated by PKA at Ser68 and by PKC at Ser63, Ser68 and Thr69 (Ser69 in mouse). Ser63 and Ser68 of PLM are significantly phosphorylated 'at rest’ by PKC in ventricular myocytes. Badrilla offers antibodies to all of these phosphorylated forms.
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A recent review focusing on the regulation of the cardiac Na pump at the protein and enzyme level and regulation by its accessory protein phospholemman:
Novel regulation of cardiac Na pump via phospholemman. J Mol Cell Cardiol. 2013 | Article
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