EXPRESSION OF PLASMA-MEMBRANE CA2-PUMP EPITOPES IN HUMAN PLATELETS AND MEGAKARYOBLASTS()

Human megakaryoblastic cells (platelet precursor cells) grown in cultu re were sectioned for immunohistochemistry. Incubating these cells wit h a monoclonal antibody (JA8) directed against the human erythrocyte C a2+ pump showed specific staining of the plasma membranes. PCR analysi s of RNA from these cells demonstrated specific sequences for type HPM CA1, HPMCA2 and HPMCA4 Ca2+ pump isoforms. Western blot analysis of me gakaryoblastic cells, whole platelets, and platelet membranes using mo noclonal antibodies JA8, 5F10, and 3C2, directed against plasma membra ne Ca2+ pump showed staining of a major band of M(r) 120,000. Taken to gether, these studies demonstrate the existence of plasma membrane Ca2 + pump epitopes in human platelets and megakaryoblastic cells.