Zn Ž016 M. 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 ŽDanio rerio. were studied in three experiments. Apical Cd uptake was
decreased by Zn in all three experiments. In fish exposed to 1600 nM Cd Žexperiment 1., apical Cd uptake showed
saturation kinetics at 2 and 4 M Zn, and a competitive interaction was indicated. At 16 M Zn, Cd uptake increased
linearly. Cadmium influx did not show saturation kinetics, but was inhibited by 16 M Zn at low Cd exposure
concentrations. In fish exposed to 0.1600 nM Cd Žexperiment 2., Cd uptake was inhibited by 16 M Zn, whereas at 30
nM Cd uptake was inhibited by 2 M Zn. Similarly, 2 M Zn did not influence Cd uptake in fish exposed to 0.12 nM
Cd Žexperiment 3., whereas 2 M Zn inhibited uptake at 830 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. 2001 Elsevier Science Inc. All rights reserved.