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

Abstract

Recent studies suggested the probable involvement of an apical iron (Fe(2+)) 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 Fe(2+) uptake and its interactions with cadmium and lead in isolated enterocytes of freshwater rainbow trout (Oncorhynchus mykiss). The expressions of two DMT1 isoforms (Nramp-beta and -gamma) were recorded along the entire gastrointestinal tract of fish as well as in the enterocytes. Fe(2+) uptake in isolated enterocytes was saturable and sensitive to the proton gradient and membrane potential, suggesting DMT1-mediated transport. Both cadmium and lead inhibited Fe(2+) uptake in isolated enterocytes in a concentration-dependent manner, and lead appeared to be a stronger inhibitor than cadmium. The kinetic characterization of Fe(2+) uptake revealed that the apparent affinity of uptake was significantly decreased (increased K(m)) in the presence of either cadmium or lead, whereas the maximum uptake rate (J(max)) remained unchanged-indicating that the interaction between Fe(2+) 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.