Iron accumulation in bronchial epithelial cells is dependent on concurrent sodium transport

Abstract

Airway epithelial cells prevent damaging effects of extracellular iron by taking up the metal and sequestering it within intracellular ferritin. Epithelial iron transport is associated with transcellular movement of other cations including changes in the expression or activity of Na, K-ATPase and epithelial Na⁺ channel (ENaC). Given this relationship between iron and Na⁺, we hypothesized that iron uptake by airway epithelial cells requires concurrent Na⁺ transport. In preliminary studies, we found that Na⁺-free buffer blocked iron uptake by human airway epithelial cell. Na⁺ channels inhibitors, including furosemide, bumetanide, and ethylisopropyl amiloride (EIPA) significantly decreased epithelial cell concentrations of non-heme iron suggesting that Na⁺-dependent iron accumulation involves generalized Na⁺ flux into the cells rather than participation of one or more specific Na⁺ channels. In addition, efflux of K⁺ was detected during iron uptake, as was the influx of phosphate to balance the inward movement of cations. Together, these data demonstrate that intracellular iron accumulation by airway epithelium requires concurrent Na⁺/K⁺exchange.