AJP - Heart Calcium Transients and Cell-Sarcomere
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Am J Physiol Heart Circ Physiol 294: H613-H621, 2008. First published December 7, 2007; doi:10.1152/ajpheart.01332.2007
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Characterization of the phospholemman knockout mouse heart: depressed left ventricular function with increased Na-K-ATPase activity

James R. Bell,1,* Erika Kennington,1,* William Fuller,1 Kushal Dighe,1 Pamela Donoghue,2 James E. Clark,1 Li-Guo Jia,3 Amy L. Tucker,3 J. Randall Moorman,3 Michael S. Marber,1 Philip Eaton,1 Michael J. Dunn,2 and Michael J. Shattock1

1Cardiovascular Division, King's College London, Rayne Institute, St Thomas' Hospital, London, United Kingdom; 2Proteome Research Centre, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin, Ireland; and 3Cardiovascular Division, Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville, Virginia

Submitted 13 November 2007 ; accepted in final form 3 December 2007

Phospholemman (PLM, FXYD1), abundantly expressed in the heart, is the primary cardiac sarcolemmal substrate for PKA and PKC. Evidence supports the hypothesis that PLM is part of the cardiac Na-K pump complex and provides the link between kinase activity and pump modulation. PLM has also been proposed to modulate Na/Ca exchanger activity and may be involved in cell volume regulation. This study characterized the phenotype of the PLM knockout (KO) mouse heart to further our understanding of PLM function in the heart. PLM KO mice were bred on a congenic C57/BL6 background. In vivo conductance catheter measurements exhibited a mildly depressed cardiac contractile function in PLM KO mice, which was exacerbated when hearts were isolated and Langendorff perfused. There were no significant differences in action potential morphology in paced Langendorff-perfused hearts. Depressed contractile function was associated with a mild cardiac hypertrophy in PLM KO mice. Biochemical analysis of crude ventricular homogenates showed a significant increase in Na-K-ATPase activity in PLM KO hearts compared with wild-type controls. SDS-PAGE and Western blot analysis of ventricular homogenates revealed small, nonsignificant changes in Na- K-ATPase subunit expression, with two-dimensional gel (isoelectric focusing, SDS-PAGE) analysis revealing minimal changes in ventricular protein expression, indicating that deletion of PLM was the primary reason for the observed PLM KO phenotype. These studies demonstrate that PLM plays an important role in the contractile function of the normoxic mouse heart. Data are consistent with the hypothesis that PLM modulates Na-K-ATPase activity, indirectly affecting intracellular Ca and hence contractile function.

FXYD1; contractile function; intracellular sodium regulation


Address for reprint requests and other correspondence: M. J. Shattock, Cardiac Physiology, King's College London, Cardiovascular Division, Rayne Institute, St Thomas' Hospital, London SE1 7EH (e-mail: michael.shattock{at}kcl.ac.uk)




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