Distribution of ion transport mRNAs throughout murine nose and lung

Evidence of absorptive or secretory ion transport in different respiratory regions of the mouse was sought by assessing the regional distribution of a lpha-, beta-, and gamma- epithelial sodium channel (ENaC; Na+ absorptive), cystic fibrosis transmembrane conductor regulator (CFTR), and Na+-K+- 2Cl(- ) cotransporter mRNAs. High levels of ENaC subunit expression were found in nasal surface epithelium and gland ducts. CFTR was expressed in both super ficial nasal respiratory epithelium and glands. These results are consisten t with basal amiloride-sensitive Na+ absorption and cAMP-dependent Cl- secr etion in murine nasal epithelia. Expression of all three ENaC subunits incr eased progressively from trachea to terminal bronchioles. Intermediate leve ls of CFTR and cotransporter expression in bronchial epithelium diminished in bronchioles. The low abundance of CFTR mRNA throughout murine pulmonary epithelium is consistent with functional data that attributes Cl- secretion predominantly to an alternative Cl- channel. alpha-ENaC as the only mRNA f ound in all regions of airway epithelia is consistent with the alpha-subuni t as requisite for Na+ absorption, and the increased expression of alpha-, beta-, and gamma-ENaC in distal airways suggests a greater absorptive capab ility in this region.