5-(N-ETHYL-N-ISOPROPYL)AMILORIDE SENSITIVE NA-CELLS( CURRENTS IN INTACT FETAL DISTAL LUNG EPITHELIAL)

To determine whether primary cultures of rat fetal distal lung epithel ium (FDLE) possessed L-type Na+ channels on their plasma membrane we p erformed experiments with 5-(N-ethyl-N-isopropyl)amiloride (EIPA) and other amiloride analogs. Short-circuit current (I(sc)) was decreased b y the apical application of amiloride and benzamil, but was unaffected by 10 muM dimethylamiloride (DMA). EIPA decreased I(sc) when added to either the apical or basal sides. Greatest effects were seen with bil ateral EIPA, where half-maximal effects occurred in the micromolar ran ge. Measurements of intracellular pH with the fluorescent dye BCECF de monstrated that DMA impaired (IC50 = 71 nM) the ability of FDLE to rec over from intracellular acidification. Nystatin perforated patch clamp techniques showed that FDLE had nonrectifying Na+ currents but no det ectable Cl- currents. The whole-cell currents were reversibly decrease d by 20 muM concentrations of EIPA, benzamil. and amiloride but were u naffected by 20 muM DMA. These studies indicate that there are EIPA-se nsitive Na+ conductances in intact FDLE and suggest the presence of L- type Na+ conductances on their apical membrane and EIPA-sensitive K+ c hannels on the basolateral membrane.