CA2-TRANSPORTING ATPASE, PHOSPHOLAMBAN, AND CALSEQUESTRIN LEVELS IN NONFAILING AND FAILING HUMAN MYOCARDIUM()

Background Observations of abnormalities in the diastolic components o f intracellular Ca2+ transients in failing human left ventricular myoc ardium have raised the possibility that reductions in the level or fun ction of sarcoplasmic reticulum proteins involved in Ca2+ transport co ntribute to the pathophysiology of dilated cardiomyopathy in humans. F unctional assays, however, have revealed no differences in ATP-depende nt Ca2+ transport or its modulation by phospholamban in sarcoplasmic r eticulum-enriched microsomes prepared from nonfailing and failing huma n left ventricular myocardium. The purpose of the present study was to quantify protein levels of Ca2+-transporting ATPase, phospholamban, a nd calsequestrin directly in nonfailing and failing human left ventric ular myocardium. Methods and Results Total protein extracts were prepa red from nonfailing left ventricular myocardium from the hearts of unm atched organ donors with normal left ventricular contractility (n=6) a nd from failing left ventricular myocardium from the excised hearts of transplant recipients with class TV heart failure resulting from idio pathic dilated cardiomyopathy (n=6). Ca2+-transporting ATPase, phospho lamban, and calsequestrin contents were determined by quantitative imm unoblotting with monoclonal and affinity-purified polyclonal antibodie s. The levels of the three proteins were identical in nonfailing and f ailing human left ventricular myocardium. Conclusions These results in dicate that protein levels of Ca2+-transporting ATPase, phospholamban, and calsequestrin are not diminished in failing human left ventricula r myocardium and that downregulation of the Ca2+-transporting ATPase a nd phospholamban is not part of the molecular pathophysiology of dilat ed cardiomyopathy in humans.