Amiloride-insensitive Na+ and fluid absorption in the mammalian distal lung

The ability of the distal lung epithelia to actively transport Na+, with Cl- and water following, from the alveolar spaces inversely correlates with morbidity and mortality of infants, children, and adults with alveolar pulmonary edema. It is now recognized, in contrast to many other Na+ transporting epithelia, that at least half of this active transport is not sensitive to amiloride, which inhibits the epithelial Na+ channel. This paper reviews amiloride-insensitive Na+ and fluid transport in the mammalian distal lung unit under basal conditions and speculates on potential explanations for this amiloride-insensitive transport. It also provides new information, using primary cultures of rat fetal distal lung epithelia and alveolar type II cells grown under submersion and air-liquid interface culture conditions, regarding putative blockers of this transport.