Electron microscopy of the continuous membrane system in a large heliozoon Echinosphaerium

Fine structure of the membrane system was examined in a large heliozoon, Echinosphaerium akamae, especially by means of negative staining and thin sectioning under the electron microscope. In addition to solitary membranous organelles such as mitochondrion, Golgi apparatus and nuclear envelope, there was found a continuous membrane system within the axopodium and the peripheral region of the cell body. By applying the isolation medium containing 4 mM glycerol, 2 mM MgSO(4), 1 mM EGTA, 0.05% Triton X-100 and 5 mM MES (pH 6.8), the membranous structures could be easily isolated without giving much distortion. However, pretreatment with 0.5 mM NaN(3) and 50 mM EDTA was necessarily required for isolating them fruitfully. The membrane system isolated from the cell showed tubular and balloon-like appearances both of which were connected with each other. Finally, the system was discussed about its function.