Cadmium and zinc induction of ZnT-1 mRNA in an established carp cell line

The cDNA of a zinc transporter-1 (ZnT-1) gene was cloned from an established cell line derived from common carp (Cyprinus carpio) using rapid amplification of cDNA ends (RACE). Using real-time quantitative PCR, we showed that both zinc (Zn) and cadmium (Cd) transiently upregulate ZnT-1 mRNA to comparable levels. The loosely bound cellular Zn pool, as estimated using the Zn-specific probe FluoZin-3, was increased threefold after exposure to 250 μM ZnCl2. Correspondingly, the ZnT-1 mRNA level at 24 h was induced about fivefold, reflecting the need for more zinc export capacity. Total cellular zinc levels were not different from the controls after 72 h of exposure to 10, 50, or 250 μM ZnCl2. A loss of total cellular Zn but little labile zinc changes were observed with up to 25 μM Cd. At 72 h, the total Zn was partially restored to the control levels, only 1 μM Cd allowed for a full recovery. Downregulation of ZnT-1 mRNA and partial loss of loosely bound Zn were observed with 50 μM Cd. Our results clearly show that although Zn and Cd can both regulate Zn export in EPC cells, the effects on the cellular Zn pools are quite different.