The effects of topoisomerase I inhibitors on the ultrastructure of T. cruzi epimastigotes. (a) Control parasite, showing the typical organization of the nucleus containing the condensed heterochromatin (ht) around the nucleolus (nu), the bar shape kinetoplast (k) and the mitochondrion (m). (b) When T. cruzi was treated with 300 μM topotecan for 72 h, the cells presented an unpacking of nuclear heterochromatin and mitochondrial swelling (m), especially in the kinetoplast (k) region. (c) T. cruzi treated with 300 μM of irinotecan for 72 h, showing a slight unpacking of nuclear heterochromatin (ht). gc, Golgi complex; f, flagellum. (A) and (B) Bars = 2 μm. (C) Bars = 1 μm.