COMPARATIVE ASPECTS OF ACTIONS OF A SHORT-CHAIN PHOSPHOLIPID ON EPITHELIAL NA+ CHANNELS AND TIGHT JUNCTION CONDUCTANCE

Ion transport in both the frog skin (a high resistance epithelium) and the rabbit nasal airway epithelium (a low-resistance epithelium) are dominated by electrogenic Na+ absorption via apical membrane amiloride -sensitive Na+ channels, and short-circuit current (I-SC) is essential ly a measure of Nai absorption in both epithelia. In both epithelia, m ucosal application of the short-chain phospholipid didecanoyl-L-alpha- phosphatidylcholine (DDPC) dose-dependently inhibited the amiloride-se nsitive I-SC and caused an initial decrease in epithelial conductance (G(t)) followed by an increase in G(t) to steady-state values above co ntrol level. The effects were reversible. It is concluded that DDPC (a ) inhibits epithelial amiloride-sensitive Na+ channels and (b) induces an increase in paracellular tight junction conductance. These effects may involve changes in nonspecific lipid-protein interactions at the cell membrane level. (C) 1997 Elsevier Science Inc.