Cadmium Uptake and Defense Mechanism in Insect Cells

The uptake of cadmium and the defense mechanism against this heavy metal were studied in theAedes albopictusC6/36 cell line. The internalization of cadmium was a very quick process and exhibited saturation kinetics over the metal concentration gradient (1.37 to 131 μmol/L). Cd toxicity and influx were both shown to be temperature dependent. The uptake was not influenced by a 2,4-dinitrophenol pretreatment but was significantly decreased by the Ca2+antagonist verapamil. These data suggest that cadmium is readily taken up through mediated transport, not requiring metabolic energy. A considerable amount of the metal passes through the Ca2+channels, but probably (an)other transporting molecule(s) also play(s) an important role in the uptake process. The remarkable, nonsigmoid viability pattern of Cd-treated cultures suggests that CdCl2concentrations above 33 μmol/L induce a cellular defense system. This phenomenon went together with increased protein synthesis. We found a major induction of a group consisting of 71-, 75-, and 78-kDa proteins, probably belonging to the HSP70 family, as similar proteins were induced by heat shock. A slight induction of a 120-kDa protein also occurred. At the highest Cd concentrations 98-, 108-, and 110-kDa proteins were induced. These data suggest that heat shock proteins may play an important role in theAedescell protection against Cd insult.