Identification and characterization of proteins in sarcoplasmic reticulum from normal and failing human left ventricles

Abstract

Monoclonal and polyclonal antibodies to the major sarcoplasmic reticulum proteins of rabbit skeletal and canine cardiac muscle have been used to identify and characterize the corresponding components of human cardiac sarcoplasmic reticulum. The Ca 2+-transporting ATPase of human cardiac sarcoplasmic reticulum was identified as a 105000-Da protein antigenically distinct from its rabbit skeletal muscle counterpart. Human cardiac sarcoplasmic reticulum also contained 53000- 155000- and 165000-Da glycoproteins antigenically related to the low and high molecular weight glycoproteins of canine cardiac and rabbit skeletal muscle sarcoplasmic reticulum. The ryanodine-sensitive Ca 2+ channel of human cardiac sarcoplasmic reticulum was identified as a 400000-Da protein antigenically related to its counterparts in canine cardiac and rabbit skeletal muscle. Human cardiac calsequestrin was identified as a 52000-Da protein. Human phospholamban was identified as a 29000-Da substrate for phosphorylation by cAMP-dependent protein kinase. Immunoblots of sarcoplasmic reticulum from the normal left ventricles of four unmatched organ donors and the excised failing left ventricles of nine patients with idiopathic dilated cardiomyopathy were compared in search of qualitative differences in the protein patterns of the failing hearts. No such differences were found with respect to the Ca 2+ ATPase, the 53000-Da glycoprotein, the ryanodine-sensitive Ca 2+ channel, calsequestrin or phospholamban. In contrast, the 165000-Da glycoprotein band, present in all four preparations from non-failing hearts, was absent from three of nine preparations from failing hearts, and staining of the 155000-Da glycoprotein in these three preparations appeared to be relatively increased. The absence of the 165000-Da glycoprotein band may identify or reflect a pathogenetic mechanism in a subset of patients with idiopathic dilated cardiomyopathy.