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

1 Program in Physiology and Experimental Medicine of the Hospital for Sick Children Research Institute and the Departments of 2 Pediatrics and 3 Physiology, University of Toronto, Toronto, Ontario, Canada 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. sodium Address for reprint requests and other correspondence: H. O'Brodovich, Univ. of Toronto, Hospital for Sick Children, 555 Univ. Ave., Toronto, Ontario, Canada M5G-1X8 (e-mail: hugh.obrodovich{at}sickkids.ca )