MECHANISMS INVOLVED IN INCREASED IRON UPTAKE ACROSS RAT DUODENAL BRUSH-BORDER MEMBRANE DURING HYPOXIA

1. Chronic hypoxia enhances intestinal iron transport but the cellular processes involved are poorly understood. In order to assess the effe cts of 3 days of hypoxia on iron uptake across the duodenal brush-bord er membrane, we have measured the membrane potential difference (V-m) of villus-attached enterocytes by direct microelectrode impalement and have used semiquantitative autoradiography to study changes in expres sion of iron uptake during enterocyte maturation. 2. Hypoxia increased duodenal V-m (-57.7 vs. -49.3 mV, P < 0.001). Ion substitution experi ments revealed that hyperpolarization was due, at least in part, to a reduction in brush-border Na+ permeability. 3. Autoradiography reveale d that hypoxia increased by 6-fold the rate of iron accumulation durin g enterocyte transit along the lower villus and enhanced by 3-fold the maximal accumulation of iron. Depolarization of the brush border, usi ng a high-K+-containing buffer, caused a proportionally greater reduct ion in iron uptake in control compared with hypoxic tissue suggesting that the raised iron uptake is only partly driven by brush-border hype rpolarization. 4. We conclude that hypoxia increases the expression of iron transport in duodenal brush-border membrane and an enhanced elec trical driving force may be involved in this response.