5-(N-Ethyl-N-isopropyl)amiloride sensitive Na+ currents in intact fetal distal lung epithelial cells

To determine whether primary cultures of rat fetal distal lung epithelium (FDLE) possessed L-type Na+ channels on their plasma membrane we performed experiments with 5-(N-ethyl-N-isopropyl)amiloride (EIPA) and other amiloride analogs. Short-circuit current (Isc) was decreased by the apical application of amiloride and benzamil, but was unaffected by 10 μM dimethylamiloride (DMA). EIPA decreased Isc when added to either the apical or basal sides. Greatest effects were seen with bilateral EIPA, where half-maximal effects occurred in the micromolar range. Measurements of intracellular pH with the fluorescent dye BCECF demonstrated that DMA impaired (IC50 = 71 nM) the ability of FDLE to recover from intracellular acidification. Nystatin perforated patch clamp techniques snowed that FDLE had nonrectifying Na+ currents but no detectable Cl− currents. The whole-cell currents were reversibly decreased by 20 μM concentrations of EIPA, benzamil, and amiloride but were unaffected by 20 μM DMA. These studies indicate...