The response to percutaneous transluminal coronary angioplasty: An ultrastructural study of smooth muscle cells and endothelial cells

We investigated the ultrastructure of the repair tissue formed after percutaneous transluminal coronary angioplasty (PTCA). Four hearts (6 coronary arteries) were investigated; 5 arteries after single PTCA and 1 after repeated PTCA. In the earliest lesion (5 days after PTCA), all smooth muscle cells were of a synthetic phenotype, with abundant rough endoplasmic reticulum and few myofilaments, whereas the oldest lesion (259 days after PTCA) was composed of contractile smooth muscle cells, characterized by abundant myofilaments and small amounts of rough endoplasmic reticulum. In lesions taken at intermediate times (74 and 77 days), the smooth muscle cells were of an intermediate phenotype, with rough endoplasmic reticulum and myofilaments present in approximately equal portions. Regenerating endothelial cells observed at 74 days after PTCA were characterized by a rounded shape and a paucity of intercellular connections in the form of simple junctions, which suggested an immature state. At 259 days after PTCA, the endothelial cells were more mature, as indicated by a flat shape and the presence of many tight junctions and a complete basement membrane. The findings suggest a relation between the stage of endothelial cell regeneration and the phenotype of the smooth muscle cells.