A new set of vesicles in Giardia lamblia

In the present study it was demonstrated the existence of a new set of membrane-bounded vesicles in Giardia lamblia. They were found in dividing and non-dividing trophozoites studied by routine transmission electron microscopy, freeze-fracture and Thiéry's technique. Encysting cells were not studied. These vesicles appear different to the previously reported components of the Giardia endomembranous system, such as the endoplasmic reticulum (ER), lysosome-like peripheral vesicles (PV), and the encystation-specific vesicles (ESV) that appear during trophozoite differentiation into cysts. They measure 100-150 nm in diameter, and thus are smaller than the peripheral vesicles, and the encystation-specific vesicles (ESV). They were found in clusters, scattered throughout the cytoplasm, but preferentially located close to the nuclei, axonemes, median bodies, and ER profiles. These internal vesicles are roughly spherical, and their contents present different electron densities and are more electrondense than those of the peripheral vesicles. They appeared to be budding from the outer nuclear membrane envelope. These cytoplasmic vesicles were found only in cells with very good fixation. Only few cells in the same preparation exhibited these vesicles.