Heavy metal cytotoxicity studied by electron probe X-ray microanalysis of cultured rat hepatocytes

Cytotoxicity of the heavy metals gold, mercury, thallium and lead was studi ed by measuring the intracellular clement distribution of cultured rat hepa tocytes by energy dispersive electron probe X-ray microanalysis of freeze-d ried cryosections in a scanning transmission electron microscope. Exposure of the cells to aqueous solutions containing heavy metal ions in concentrat ions reaching a critical concentration caused increase of intracellular sod ium and chloride content accompanied or followed by decrease of intracellul ar potassium content. Thus, the intracellular potassium/sodium ratio drasti cally decreased from control values of approximately 10 to values below 1 b efore changes of cell morphology became visible. In experiments with gold o r mercury the decrease of the potassium/sodium ratio was preceded by transi ent cytoplasmic increase of sulfur and phosphorus. Heavy metal concentratio ns exceeding the critical concentration also caused an increase of cytoplas mic calcium concentration and finally decay of the cell structure. Cytotoxi city of heavy metals was found to increase in the order Pb, Au, Tl, Hg, Cyt otoxic effects by Au, Tl or Hg in moderate concentrations were reduced by s imultaneous addition of Zn or Pb to the culture medium. The results obtaine d prove electron probe X-ray microanalysis of cryosections as a sensitive p robe of cell viability. (C) 2000 Elsevier Science Ltd. All rights reserved.