Modification of the ultrastructure of Entamoeba histolytica after phagocytosis of liposomes loaded with phalloidin.

The specific actin-interacting drug phalloidin has been introduced into the cytoplasm of a highly motile amoeba, Entamoeba histolytica, by a new technique: the phagocytosis of liposomes containing phalloidin. After ingestion of these liposomes, two important modifications of the ultrastructure of the amoeba were observed. First, large nodules of densely packed fine filaments are formed, which may be due to the polymerization of actin induced by the release of phalloidin within the cell's cytoplasm. Second, phalloidin induces the proliferation of ribosome crystals known as chromatoid bodies in encysted cells. This formation could be the direct consequence of the action of phalloidin on actin, where filaments form and ribosomes detach from the original oligo or polymers. However, it could also result from an unspecific toxic effect on the amoeba which, under physiological stress, starts to encyst and show multiplication of these chromatoid bodies upon encystment.