Low Voltage Transmission Electron Microscopy in Cell Biology

Abstract

Application of low voltage transmission electron microscopy in cell biology revealed new aspects in some cellular compartments. A Delong LVEM5 transmission electron microscope with 5kV electron source was used. Incident beam with electron energy in the 5kV range has the advantage of generating considerable contrast in sections of non‐osmicated, non‐counterstained with heavy metals tissues. As beam penetration is reduced at low accelerating voltages, ultrathin (30–50nm) tissue sections were prepared. Examination of such sections with low voltage transmission electron microscopy, revealed the existence of a sub‐compartmentalization in pancreatic secretory granules. This partition reflects internal segregation of the granule content as previously demonstrated by high resolution cytochemistry. In SV‐40 infected pancreatic cells, the viral particles were revealed in compartments such as the secretory granules. In mitochondria, the use of the low voltage microscopy enabled visualization of membrane granules or oxysomes (oxidative phosphorylation) on the inner‐mitochondrial membrane. Examination of the nuclear matrix revealed the existence of sequences of chains of very small granules linked to each other by single threads. Such morphological observations were not possible by conventional transmission electron microscopy. In addition, we were able to carry out high resolution immunogold on non‐stained ultrathin tissue sections and revealed the immunolabeling by low voltage electron microscopy. Indeed, 10nm gold particles were reliably visualized, mapping particular proteins and bringing additional advantage to this new approach. By enhancing contrast on non‐osmicated, non‐counterstained ultrathin tissue sections, low‐voltage transmission electron microscopy is able to reveal new substructural details in cellular compartments. Combination with the immunogold can further assign functional properties to these new substructures.