Fig. 6. Effect of extracellular zinc concentration on zinc content and cell viability. (A) Zinc concentrations in cells were measured by electrothermal atomic absorption spectrophotometry in either normal or zinc-supplemented medium. Values are expressed as zinc concentration normalized for protein content. *P<0.01 vs control; **P<0.05 vs non-supplemented cells. White bars, control cells; gray bars, INS-1E-ZnT8-EGFP cells. (B) After incubation with different concentrations of zinc sulphate, the cell viability was determined by MTT assay. Values are the mean ± s.e.m. of at least ten independent experiments White bars, control cells; gray bars, INS-1E-ZnT8-EGFP cells. (C) After incubation with different concentrations of the zinc chelator TPEN, the cell viability was determined by MTT assay. Values are the mean ± s.e.m. of at least ten independent experiments. *P<0.05 vs control; **P<0.005 vs control. White bars, control cells; gray bars, INS-1E-ZnT8-EGFP cells.