The influence of zinc on apical uptake of cadmium in the gills and cadmium influx to the circulatory system in zebrafish (Danio rerio)

Zn (0-16 muM) effects on apical Cd uptake from the water into the branchial epithelium and influx of Cd from the water to the circulatory system in zebrafish (Danio rerio) were studied in three experiments. Apical Cd uptake was decreased by Zn in all three experiments. In fish exposed to 1-600 nM Cd (experiment 1), apical Cd uptake showed saturation kinetics at 2 and 4 muM Zn, and a competitive interaction was indicated. At 16 muM Zn, Cd uptake increased linearly. Cadmium influx did not show saturation kinetics, but was inhibited by 16 muM Zn at low Cd exposure concentrations. In fish exposed to 0.1-600 nM Cd (experiment 2), Cd uptake was inhibited by 16 muM Zn, whereas at 30 nM Cd uptake was inhibited by 2 muM Zn. Similarly, 2 muM Zn did not influence Cd uptake in fish exposed to 0.1-2 nM Cd (experiment 3), whereas 2 muM Zn inhibited uptake at 8-30 nM Cd. Zinc also inhibited Cd influx at higher Cd concentrations. However, at lower Cd exposures, a Zn-induced increased influx was indicated. Zinc influences the Cd uptake and influx processes at several sites in the branchial epithelial cells, indicating that influx of Zn2+ and Cd2+ occurs through common pathways. (C) 2001 Elsevier Science Inc. All rights reserved.