The ultrastructural effect and subcellular localization of mercuric chloride and methylmercuric chloride in insect cells (Aedes albopictusC6/36)

Abstract.The ultrastructural effects of mercuric chloride (Hg) and methylmercuric chloride (MeHg) were studied in theAedes albopictusC6/36 cell line. Both metal salts caused nuclear indentations, chromatin clumping and proliferation of the nucleolus. The mitochondria became pleomorphous. An increase of both free and membrane-bound ribosomes, swelling of the rough endoplasmic reticulum caused by accumulated protein and the appearance of well developed Golgi stacks all indicated the activation of protein synthesis. The activation was probably a cellular response to general stress, and the synthesized proteins may be members of the heat shock protein family. Apart from these common ultrastructural features, Hg-treated cells showed typical clusters of small electron-lucent vacuoles near the Golgi stacks. In cells exposed to MeHg, cytoplasmic tube-like structures were often observed and the disorganization of the organelles together with the appearance of blebs suggested disruption of the microtubules. Mercury accumulation was localized by an autometallographical silver staining technique both at the light and electron microscopic level; silver deposits were quantified by image analysis. For both Hg- and MeHg-treated cells, the degree of silver staining increased rapidly with increasing exposure time, but a considerable heterogeneity within the cell population was found. Lysosomes proved to be the major mercury storage sites in theAedescells and silver deposits could already be found after 30 min of Hg treatment. At sublethal concentrations, Hg inhibited the lysosomal marker enzyme acid phosphatase to some extent. For MeHg, no effect on this enzyme was found.