Molecular evidence and physiological characterization of iron absorption in isolated enterocytes of rainbow trout (Oncorhynchus mykiss): Implications for dietary cadmium and lead absorption

Recent studies suggested the probable involvement of an apical iron (Fe2+) transporter, the divalent metal transporter-1 (DMT1), in the uptake of several divalent metals in fish. The present study examined the gastrointestinal expression of the DMT1 gene, and investigated the kinetics of Fe2+ uptake and its interactions with cadmium and lead in isolated enterocytes of freshwater rainbow trout (Oncorhynchus mykiss). The expressions of two DMT1 isoforms (Nramp-β and -γ) were recorded along the entire gastrointestinal tract of fish as well as in the enterocytes. Fe2+ uptake in isolated enterocytes was saturable and sensitive to the proton gradient and membrane potential, suggesting DMT1-mediated transport. Both cadmium and lead inhibited Fe2+ uptake in isolated enterocytes in a concentration-dependent manner, and lead appeared to be a stronger inhibitor than cadmium. The kinetic characterization of Fe2+ uptake revealed that the apparent affinity of uptake was significantly decreased (increased Km) in the presence of either cadmium or lead, whereas the maximum uptake rate (Jmax) remained unchanged—indicating that the interaction between Fe2+ and cadmium or lead is competitive in nature. Overall, our study suggests that the uptake of dietary cadmium and lead may occur via the iron-transporting pathway in fish.