Detection of apoptotic cells with TUNEL assay. (A and B) CECs isolated from donors with AMI or UA. (C) Control apoptotic HL60 cells. Nuclei of CECs are counterstained red with propidium iodide. A large majority of CECs including endothelial sheets are negative (A). Only rare cells show DNA breaks (B). The control apoptotic HL60 cells are positive (C).