Regulation of Distal Lung Fluid Absorption by Membrane Components

摘要

Near the end of gestation, the direction of ion and fluid flow across the alveolar epithelium rapidly changes from secretion to absorption. Thus, the relative cell membrane location of epithelial Na channels (ENaC) and cystic fibrosis transmembrane regulator (CFTR) Cl channels during late fetal lung development and after maternal interleukin-1beta (IL-1beta) pretreatment was the focus of our study. Western blot analysis after sucrose gradient separation of caveolin-1-(cav-1)-rich membrane regions (CRR) and non cav-1-rich membrane regions (non-CRR) revealed primary CRR ENaC localization at gestation day (GD) 61 in guinea pigs. Correlating with the natural induction of distal lung fluid absorption, ENaC appeared in the non-CRR at GD68. IL-1beta induced conversion to distal lung fluid absorption at GD61 was associated with ENaC non-CRR presence and CFTR CRR presence, suggesting that relative ENaC and CFTR locations induced distal lung fluid absorption and decreased fluid secretion. Instilling fetal lungs with the CRR disrupting agent methyl-beta-cyclodextrin resulted in the conversion from fluid secretion to absorption and ENaC non-CRR presence at GD61. Co-immunoprecipitation (co-IP) of cav-1 with alpha- and beta-ENaC demonstrated a reduced co-IP with increased GD and after IL-1beta pretreatment. On the other hand, a co-IP of cav-1 with CFTR demonstrated an increased co-IP with increasing GD and after IL-1beta pretreatment. In addition, treatment with phosphatidylinositol-4,5-bisphosphate (PIP2) induced the conversion of the lungs early in development from fluid secretion to absorption. This concept may provide novel molecular mechanisms for the rapid transition from fetal distal lung fluid secretion to absorption in near-term lungs.