Author:
Li Tianbo,Folkesson Hans G.
Abstract
We used siRNA against the α-ENaC (epithelial Na channel) subunit to investigate ENaC involvement in lung fluid absorption in rats by the impermeable tracer technique during baseline and after β-adrenoceptor stimulation by terbutaline. Terbutaline stimulation of lung fluid absorption increased fluid absorption by 165% in pSi-0-pretreated rat lungs (irrelevant siRNA-generating plasmid). Terbutaline failed to increase lung fluid absorption in rats given the specific α-ENaC siRNA-generating plasmid (pSi-4). pSi-4 pretreatment reduced baseline lung fluid absorption by ∼30%. α-ENaC was undetectable in pSi-4-pretreated lungs, regardless of condition but was normal in pSi-0-pretreated lungs. We carried out a dose-response analysis where rats were given 0–200 μg/kg body wt pSi-4, and α-ENaC mRNA and protein expressions were analyzed. To reach IC50for α-ENaC mRNA expression, 32 μg/kg body wt pSi-4 was needed, and to reach IC50for α-ENaC protein expression, 59 μg/kg body wt pSi-4 was needed. We tested for lung tissue specificity and found no changes in β-ENaC expression, at either mRNA or protein level, as well as no changes in α1-Na-K-ATPase protein expression. We isolated alveolar epithelial type II cells 24 h after in vivo pSi-4 pretreatment. In these cells, α-ENaC mRNA was undetectable, demonstrating that alveolar epithelial ENaC expression was attenuated after intratracheal α-ENaC siRNA-generating plasmid DNA instillation. We tested for organ specificity and found no changes in kidney α- and β-ENaC mRNA and protein expression. Thus we provide conclusive evidence that β-adrenoceptor stimulation of lung fluid absorption is critically ENaC dependent, whereas baseline lung fluid absorption seemed less ENaC dependent.
Publisher
American Physiological Society
Subject
Cell Biology,Physiology (medical),Pulmonary and Respiratory Medicine,Physiology
Cited by
66 articles.
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