title: 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.
authors.affiliation: Toxicology Centre, University of Saskatchewan, Saskatoon, SK, Canada S7N 5B3.
authors.forename: Raymond W M
authors.initials: RW
authors.lastname: Kwong
authors.forename: Jose A
authors.initials: JA
authors.lastname: Andrés
authors.forename: Som
authors.initials: S
authors.lastname: Niyogi
mesh_terms: D000042:Absorption; D000818:Animals; D002104:Cadmium / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020895:Enterocytes / Q000187:drug effects / Q000378:metabolism*; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D007854:Lead / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D000099236:Solute Carrier Family 11, Member 2
chemical_list: D002104:Cadmium; D027682:Cation Transport Proteins; D007501:Iron; D007854:Lead; D012333:RNA, Messenger; D014874:Water Pollutants, Chemical; D000099236:Solute Carrier Family 11, Member 2