MOLECULAR MECHANISMS OF INTESTINAL COPPER TRANSPORT DURING IRON‐DEFICIENCY

We previously described novel changes in the expression of genes related to intestinal copper ion homeostasis (e.g. Atp7a, Dmt1, Dcytb and metallothionein) in the doudenal epithelium of iron‐deprived rats across several stages of post‐natal development (suckling through adulthood). We also noted increased intestinal copper levels. We thus hypothesize that increased intestinal copper transport occurs during iron deficiency. Additional studies demonstrate strong induction of ATP7A protein on the brush‐border (BB) and basolateral membranes of enterocytes and DMT1 protein expression on the BBM. We surmise that ATP7A is responsible for increased intestinal copper ion efflux, but the identity of the copper uptake protein is not known. We have thus developed a fluorescent uptake assay, utilizing the metal‐binding fluorophore calcein, to perform functional transport studies to define the kinetic properties of the copper ion transporter in BBM vesicles isolated from iron‐deficient rats. These analyses will allow us to predict the molecular identity of the apical transporter, as ATP7A, DMT1 and CTR1 (another known intestinal copper transporter) have distinct functional properties. Our preliminary data show robust copper transport across BBM vesicles during iron‐deficiency when copper is in the reduced state (e.g. Cu1+) and that transport is minimal in vesicles purified from rats with normal iron status.