LOCALIZATION OF EPITHELIAL SODIUM-CHANNEL SUBUNIT MESSENGER-RNAS IN ADULT-RAT LUNG BY IN-SITU HYBRIDIZATION

The transport of Na+ through amiloride-sensitive sodium channels (ENaC ) plays a major role in the absorption of fluid across the pulmonary e pithelium. The proteins forming the ENaC channel are encoded by three genes in the rat (alpha-, beta-, and gamma-rENaC). According to Northe rn blot, all three subunit mRNAs were expressed in adult rat lung. Eac h subunit was expressed as a single transcript of similar to 3.7, 2.2, and 3.2 kb for alpha-, beta-, and gamma-rENaC, respectively. To local ize the alpha-, beta-, and gamma-rENaC subunit mRNAs, we used in situ hybridization. Frozen and paraffin-embedded tissues were hybridized wi th sense and antisense S-35-labeled riboprobes. The alpha-rENaC mRNA w as most abundant and was expressed diffusely in epithelia of the trach ea, bronchi, bronchioles, and alveoli. At the alveolar level, alpha-rE NaC was expressed in type II cells. The beta- and gamma-rENaC mRNAs we re most abundant in the bronchial and bronchiolar epithelia. All three subunits were expressed in the renal cortical collecting duct in a pa ttern similar to that previously reported by other investigators. Thus the rENaC subunit mRNAs are expressed in regions of the lung where fu nctional Na+ absorption is found. These results are consistent with an important role for ENaC in the absorption of Na+ and fluid across the pulmonary epithelium in all regions of the lung.