The Journal of Nutrition Vol. 127 No. 6 June 1997, pp. 1092-1098
Copyright ©1997 by the American Society for Nutritional Sciences

Iron Uptake by Rabbit Intestinal Brush Border Membrane Vesicles Involves Movement Through the Outer Surface, Membrane Interior, Inner Surface and Aqueous Interior

Manuscript received 7 October 1996. Initial reviews completed 2 December 1996. Revision accepted 20 February 1997.

Gloria Perewusnyk^* and Felix Funk^,

^* Institute of Medical Radiobiology, University of Zurich and Paul Scherrer Institute, CH-5234 Villigen PSI, Switzerland; and  Institute of Terrestrial Ecology, Swiss Federal Institute of Technology (ETH) Zurich, CH-8952 Schlieren, Switzerland

Iron uptake in rabbit brush border membrane vesicles was measured in the presence of nitrilotriacetate. The complexes formed ranged from stable mononuclear species to hydrolyzed polynuclear complexes and are considered as a good model for nutritional iron compounds with respect to their chemical reactivity. Uptake includes both binding to and penetration through the membrane. A strategy was developed to localize iron in the following four compartments: outer membrane surface, membrane interior, inner membrane surface and aqueous phase within the vesicles. Both surfaces as well as the membrane interior revealed a high metal binding capacity. After an incubation for 10 min with 182 µmol/L iron and 364 µmol/L nitrilotriacetate, 35% of total vesicle iron was found to be bound to the outer membrane surface, 34% to the inner membrane surface, and 23% was not accessible to EDTA. Thus, by adsorption of polynuclear iron complexes to the outer surface, the residence time of iron may be prolonged. The remaining 8% of total iron was in the aqueous phase within the vesicles. Nitrilotriacetate enters the rabbit vesicles in a concentration-dependent manner. As a consequence, iron concentration in the aqueous phase within the vesicles will be driven to the medium equilibrium concentration.