Short Term Exposure of Sheep Tracheal Epithelium to Cigarette Smoke Extract Reduces ENaC Current: A Pilot Study

Cigarette smoke has been shown to induce a phenotype in humans known as "acquired cystic fibrosis". This occurs because the cystic fibrosis transmembrane conductance regulator (CFTR) functions are impaired systemically due to the deleterious effects of smoke components. Elucidation of cigarette smoke effects on the tracheal epithelium is important. The aim of this study was to develop an ex vivo sheep tracheal model to investigate tracheal ion function. In this model, the epithelial sodium channel (ENaC) is inhibited after exposure to cigarette smoke extract (CSE) as a proof of principle.

Tracheas were isolated from healthy sheep and the tracheal epithelium was surgically excised. Tissues were mounted in Ussing chambers and the short circuit current (I_sc) was measured after incubation with 5% CSE in PBS or PBS alone for 30 min. The function of ENaC was investigated by the addition of amiloride (10^-5M) apically. Western blot analysis was performed to assess differences in ENaC quantity after CSE exposure. Some specimens were stained with H&E for detection of histological alterations.

The amiloride effect on normal epithelium led to a significant decrease in I_sc [ΔI=33±5.92 μA/cm²; p<0.001 versus control experiments (ΔI=1.44±0.71 μA/cm²)]. After incubation with CSE, ENaC I_sc was significantly reduced (ΔI=14.80±1.96 μA/cm²; p<0.001). No differences in αENaC expression were observed between CSE-exposed and normal tracheal epithelium. Histological images post CSE incubation revealed decreases in the height of the epithelium, with basal cell hyperplasia and loss of ciliated cells.

Reduced ENaC inhibition by amiloride after CSE incubation could be due to alterations in the tracheal epithelium.