Active transport of iron by intestine: features of the two-step mechanism

Abstract

Everted gut sacs prepared from the proximal duodenum of the rat, mouse, and golden hamster can transfer iron actively, i.e. against concentration and potential gradients, from the mucosa to the serosa. The active transfer involves two steps: mucosal uptake and net transfer to the serosal surface. Oxidative metabolism is apparently required for each of the steps. Net transfer to the serosal surface is slower, more readily rate-limited, and more sharply localized to the proximal duodenum than is mucosal uptake. Both divalent and trivalent iron are taken up at the mucosal surface, but net transfer to the serosal surface is relatively specific for divalent iron. Calcium inhibits the net serosal transfer of iron at concentrations which do not inhibit the mucosal uptake. Parallel studies with loops of duodenum in living rats indicate that the active, two-step mechanism for iron absorption also functions in vivo, where the steps in the transfer are mucosal uptake followed by transport from the tissue to the blood stream.