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 α-, β-, and γ-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 superficial nasal respiratory epithelium and glands. These results are consistent with basal amiloride-sensitive Na+ absorption and cAMP-dependent Cl- secretion in murine nasal epithelia. Expression of all three ENaC subunits increased progressively from trachea to terminal bronchioles. Intermediate levels 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. α-ENaC as the only mRNA found in all regions of airway epithelia is consistent with the α-subunit as requisite for Na+ absorption, and the increased expression of α-, β-, and γ-ENaC in distal airways suggests a greater absorptive capability in this region.