IN-VIVO ANALYSIS OF FLUID TRANSPORT IN CYSTIC-FIBROSIS AIRWAY EPITHELIA OF BRONCHIAL XENOGRAFTS

An in vivo human bronchial xenograft model system was used to simultan eously analyze electrolyte and fluid transport defects in fully differ entiated human cystic fibrosis (CF) and non-CF proximal airways. CF ai rways demonstrated three discernible defects when compared with non-CF , including 1) a lack of adenosine 3',5'-cylic monophosphate (cAMP)-in ducible Cl- secretion, 2) a fourfold higher basal fluid absorption rat e, and 3) an altered regulation of fluid absorption in response to ami loride-stimulated changes in Na+ transport. A unique finding in this s tudy demonstrated that treatment of epithelia with amiloride led to a greater than threefold decrease in the rate of fluid absorption in CF tissues as contrasted to a greater than threefold increase in the rate of fluid absorption in non-CF tissues. The removal of apical Na+ from amiloride-treated non-CF xenografts was capable of ablating this amil oride-induced increase in fluid absorption. In light of the recent int eractions demonstrated between CF transmembrane conductance regulator (CFTR) and the rat epithelial, amiloride-sensitive Na+ channel, these findings implicate additional complexities between the Na+ conductance pathways and fluid transport in normal and CF proximal airways. Such findings suggest that CFTR may also regulate amiloride-insensitive Na channels.