Is the rapid Cu accumulation component fast uptake into the cells or surface adsorption of Cu?
Some of the `time zero’ control experiments in this study (Fig. 3, Table 2) revealed a rapid component of Cu accumulation that occurred in less than 1 min. This component was probably very rapid Cu uptake into the cells, rather than just surface binding (adsorption) of Cu on to the outside of the cells (Handy et al., 2002). The characteristics of the rapid component include sensitivity to ENaC inhibitors, DIDS and ice-cold chilling (Table 2), and are best explained by rapid changes in the rate of Cu transport rather than adsorption chemistry. Cells were also washed several times in 0.1 µmol l 1 EDTA, and this would chelate/wash off some of the surface-bound Cu2+. Furthermore, the Cu content of cells in Cu-free conditions (no added Cu + 1 µmol l 1 EDTA) were the same as in conditions of no added Cu (saline without EDTA) in all experiments (Figs 4, 5, 6), suggesting that surface-bound Cu was a small component relative to the total background Cu content of the cells (albeit after washing
