Unchanged Protein Levels of SERCA II and Phospholamban but Reduced Ca 2+ Uptake and Ca 2+ -ATPase Activity of Cardiac Sarcoplasmic Reticulum From Dilated Cardiomyopathy Patients Compared With Patients With Nonfailing Hearts

Abstract

Background The aim of the present study was to investigate whether Ca 2+ uptake into the sarcoplasmic reticulum (SR) is altered in failing human myocardium resulting from dilated cardiomyopathy. Methods and Results Ca 2+ -ATPase (SERCA II) activity and Ca 2+ -dependent 45 Ca 2+ uptake (oxalate supported, steady state) in isolated vesicles from the SR (VSR) and in crude membrane preparations (CSR) (free Ca 2+ , 0.01 to 100 μmol/L) from nonfailing (donor hearts, n=13) and terminally failing (heart transplants, dilated cardiomyopathy, n=17) human myocardium were studied. In the same hearts, protein levels (Western blot analysis) and mRNA levels (Northern blot analysis) of SERCA II and phospholamban were measured. Increasing concentrations of Ca 2+ were followed by an increased Ca 2+ -ATPase activity and Ca 2+ uptake. Ca 2+ uptake activity and Ca 2+ -ATPase activity in CSR preparations from failing myocardium were significantly reduced compared with nonfailing hearts (Ca 2+ -ATPase, 163±8 and 125±7 nmol ATP/mg protein per minute for nonfailing tissue and failing tissue in New York Heart Association [NYHA] class IV, respectively; Ca 2+ uptake, 7.1±0.8 and 3.5±0.3 nmol/mg protein per minute in CSR from nonfailing and NYHA class IV hearts, respectively; P <.05). In contrast, no significant difference was measured in VSR. In the same preparations (CSR and VSR), both SERCA II and phospholamban levels (Western blot technique with monoclonal antibodies) were unchanged in failing compared with nonfailing tissue. mRNA expression relative to GAPDH mRNA for SERCA IIa and for phospholamban was significantly reduced in failing human myocardium ( P <.05). Conclusions These findings provide evidence that in failing human myocardium caused by dilated cardiomyopathy, protein levels of SERCA II and phospholamban are unchanged even though mRNA levels for SERCA II and phospholamban and the SERCA II function are reduced compared with nonfailing myocardium.