Elemental composition of acidocalcisomes of Trypanosoma cruzi bloodstream trypomastigote forms

The elemental composition of acidocalcisomes present in Trypanosoma cruzi bloodstream trypomastigotes was analyzed by X-ray microanalysis. Acidocalcisomes appear as electron-dense vesicles dispersed throughout the cytoplasm. X-ray microanalysis of whole cells adhered to Formvar-coated grids showed that they contained C, O, Na, Mg, P, S, Ca and Zn, although in some acidocalcisomes iron was also detected. However, in ultra-thin sections of parasites processed according to routine procedures, most elements were lost. Living parasites were incubated with gold-labeled holo-transferrin to test if the iron was taken up by receptor-mediated endocytosis. After incubation at 4 degrees C, labeling was observed only in the flagellar pocket membrane, showing that receptors to this protein are already present in bloodstream trypomastigotes. In parasites incubated at 28 degrees C no intracellular tracer was observed, despite the labeling in the flagellar pocket membrane. Our data show that some acidocalcisomes of T. cruzi bloodstream trypomastigotes contain iron and that this element was not taken up by receptor-mediated endocytosis.