Cytoplasmic organelles of trypanosomatids: a cytochemical and stereological study

The cytoplasmic organelles of different protozoa of the family Trypanosomatidae were characterized by ultrastructural cytochemistry and stereology. Data were obtained for mitochondria, lipid inclusions, glycosomes (peroxisome-like organelle), empty membrane-bounded vacuoles, reservosomes of Trypanosoma spp., multivesicular body of Crithidia fasciculata and dense granules of Crithidia oncopelti. The stereological analysis (D = mean diameter, Vv = volume density and Nv = numerical density) was performed in glutaraldehyde-formaldehyde and osmium tetroxide-potassium ferricyanide fixed parasites, which showed an excellent preservation of the membranes and cytoplasmic organelles. Lipid inclusions, not limited by a unit membrane, appeared electron-dense after post-fixation in an osmium-imidazole buffered solution. Catalase, a peroxisomal enzyme, was detected only in the glycosomes of the lower trypanosomatids. Empty membrane-bounded vacuoles showed positive reaction when the cells were incubated in a medium specific for the detection of the lysosomal enzyme acid phosphatase. The reservosomes of Trypanosoma spp., sub-genus Schizotrypanum, could be differentiated from the multivesicular bodies of other trypanosomatids, since they lack true vesicles. They contain lipid inclusions dispersed in an electron-dense matrix which stained positively when the cells were incubated in ethanolic phosphotungstic acid to detect basic proteins.