title: Regulation of cardiac Na+/Ca2+ exchanger by phospholemman.
abstract: Phospholemman (PLM) is the first sequenced member of the FXYD family of regulators of ion transport. The mature protein has 72 amino acids and consists of an extracellular N terminus containing the signature FXYD motif, a single transmembrane (TM) domain, and a cytoplasmic C-terminal domain containing four potential sites for phosphorylation. PLM and other members of the FXYD family are known to regulate Na+-K+-ATPase. Using adenovirus-mediated gene transfer into adult rat cardiac myocytes, we showed that changes in contractility and intracellular Ca2+ homeostasis associated with PLM overexpression or downregulation are not consistent with the effects expected from inhibition of Na+-K+-ATPase by PLM. Additional studies with heterologous expression of PLM and cardiac Na+/Ca2+ exchanger 1 (NCX1) in HEK293 cells and cardiac myocytes isolated from PLM-deficient mice demonstrated by co-localization, co-immunoprecipitation, and electrophysiological and radioactive tracer uptake techniques that PLM associates with NCX1 in the sarcolemma and transverse tubules and that PLM inhibits NCX1, independent of its effects on Na+-K+-ATPase. Mutational analysis indicates that the cytoplasmic domain of PLM is required for its regulation of NCX1. In addition, experiments using phosphomimetic and phospho-deficient PLM mutants, as well as activators of protein kinases A and C, indicate that PLM phosphorylated at serine68 is the active form that inhibits NCX1. This is in sharp contrast to the finding that the unphosphorylated PLM form inhibits Na+-K+-ATPase. We conclude that PLM regulates cardiac contractility by modulating the activities of NCX and Na+-K+-ATPase.
authors: Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA. joseph.cheung@jefferson.edu
authors: Joseph Y
authors: JY
authors: Cheung
authors: Lawrence I
authors: LI
authors: Rothblum
authors: J Randall
authors: JR
authors: Moorman
authors: Amy L
authors: AL
authors: Tucker
authors: Jianliang
authors: J
authors: Song
authors: Belinda A
authors: BA
authors: Ahlers
authors: Lois L
authors: LL
authors: Carl
authors: JuFang
authors: J
authors: Wang
authors: Xue-Qian
authors: XQ
authors: Zhang
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000502:physiology*; D002460:Cell Line; D006706:Homeostasis; D006801:Humans; D047468:Immunoprecipitation; D009206:Myocardium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D000099211:Phospholamban
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D019831:Sodium-Calcium Exchanger; D000254:Sodium-Potassium-Exchanging ATPase; D000099211:Phospholamban