Ca(2+)-transporting ATPase, phospholamban, and calsequestrin levels in nonfailing and failing human myocardium.

BACKGROUND: Observations of abnormalities in the diastolic components of intracellular Ca2+ transients in failing human left ventricular myocardium have raised the possibility that reductions in the level or function of sarcoplasmic reticulum proteins involved in Ca2+ transport contribute to the pathophysiology of dilated cardiomyopathy in humans. Functional assays, however, have revealed no differences in ATP-dependent Ca2+ transport or its modulation by phospholamban in sarcoplasmic reticulum-enriched microsomes prepared from nonfailing and failing human left ventricular myocardium. The purpose of the present study was to quantify protein levels of Ca(2+)-transporting ATPase, phospholamban, and calsequestrin directly in nonfailing and failing human left ventricular myocardium. METHOD AND RESULTS: Total protein extracts were prepared from nonfailing left ventricular myocardium from the hearts of unmatched organ donors with normal left ventricular contractility (n = 6) and from failing left ventricular myocardium from the excised hearts of transplant recipients with class IV heart failure resulting from idiopathic dilated cardiomyopathy (n = 6). Ca(2+)-transporting ATPase, phospholamban, and calsequestrin contents were determined by quantitative immunoblotting with monoclonal and affinity-purified polyclonal antibodies. The levels of the three proteins were identical in nonfailing and failing human left ventricular myocardium. CONCLUSIONS: These results indicate that protein levels of Ca(2+)-transporting ATPase, phospholamban, and calsequestrin are not diminished in failing human left ventricular myocardium and that downregulation of the Ca(2+)-transporting ATPase and phospholamban is not part of the molecular pathophysiology of dilated cardiomyopathy in humans.