The role of vacuolar digestive system in preventing cadmium poisoning in Acanthamoeba castellanii.

Constituents showing cadmium affinity were found in digestive residues of the vacuolar digestive system in Acanthamoeba. Cadmium was detected by means of X-ray analysis in complexes appearing both in residues included within the digestive vacuoles and in those egested outside the cell. The digestive vacuolar system in Acanthamoeba castellanii is characterized by a particularly high turnover rate (4). Confronted with this fact, results of the present study suggest that the system is able to egest rapidly the ligand-bound cadmium. In this way protects the amoeba against serious toxic effects of the Cd-polluted environment.

Replacement of calcium by cadmium ions from Ca-affinity sites localized in different cytoplasmic compartments of Acanthamoeba cells.

In Acanthamoeba cells both Ca and Cd may be precipitated in different cytoplasmic compartments forming electron-opaque deposits, as shown in cells treated with glutaraldehyde supplied with either Ca or Cd respectively. It was found by semiquantitative X-ray microanalysis that the transfer of cells containing Ca-deposits to glutaraldehyde supplied with Cd causes a considerable replacement of Ca by Cd: in deposits formed at cell membrane, in cytoplasm, and in mitochondria the total weight percentage of Cd amounted to over 90, only in deposits formed in vacuoles the value was about 80. The replacement was not prevented by the presence of Ca in the transfer medium. When cells containing Cd-deposits were transferred to Ca-supplied medium, Cd predominated as well, its total weight percentage also amounting to over 90 in all the examined deposits. The results suggest that calcium bound in different cell structures may be easily replaced by cadmium, but not conversely, which suggests that Cd is more firmly than calcium linked to many cell constituents well preserved by fixation.