Characterization of the phospholemman knockout mouse heart: depressed left ventricular function with increased Na-K-ATPase activity.
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.
Bell
James R
JR
Cardiovascular Division, King's College London, Rayne Institute, St Thomas' Hospital, London , UK.
Kennington
Erika
E
Fuller
William
W
Dighe
Kushal
K
Donoghue
Pamela
P
Clark
James E
JE
Jia
Li-Guo
LG
Tucker
Amy L
AL
Moorman
J Randall
JR
Marber
Michael S
MS
Eaton
Philip
P
Dunn
Michael J
MJ
Shattock
Michael J
MJ
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002118:Calcium / Q000494:pharmacology; D015180:Electrophoresis, Gel, Two-Dimensional; D006321:Heart / Q000502:physiology*; D006329:Heart Conduction System / Q000502:physiology; D066298:In Vitro Techniques; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009206:Myocardium / Q000201:enzymology*; D009929:Organ Size / Q000502:physiology; D010641:Phenotype; D010750:Phosphoproteins / Q000235:genetics / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D016277:Ventricular Function, Left / Q000502:physiology
D008565:Membrane Proteins; D010750:Phosphoproteins; C069141:phospholemman; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium