Hypertonic challenge to porcine vocal folds: effects on epithelial barrier function

Abstract

Objective: Dehydration challenges can increase the chemical composition of surface fluid overlying vocal fold epithelia (hypertonic surface fluid). The vocal fold epithelium is posited to act as a barrier, shielding the lamina propria from perturbations in the airway lumen. However, the effects of hypertonic surface fluid on the barrier functions of vocal fold epithelia have not been quantified. We, therefore, sought to investigate whether hypertonic surface fluid compromises epithelial barrier function. We examined the effects of hypertonic surface fluid on vocal fold epithelial resistance, paracellular pathway morphology, and tight junction protein integrity.

Study design: Ex vivo, between group design.

Setting: Laboratory.

Methods: Porcine vocal folds (n = 24) were exposed to hypertonic or isotonic challenge and examined by electrophysiology, transmission electron microscopy, and Western blot analyses.

Results: Hypertonic, but not isotonic, challenge significantly reduced transepithelial resistance. This decrease in resistance was observed immediately after the challenge and was consistent with the appearance of dilated paracellular pathway morphology. However, hypertonic challenge did not alter protein levels of occludin, zona occludens-1, E-cadherin, or beta-catenin.

Conclusion: Hypertonic surface fluid alters epithelial barrier function in the vocal folds. Specifically, exposure to hypertonic challenges increases epithelial permeability. Given the important role of the vocal fold epithelium in shielding the underlying mucosa from inhaled pathogens and pollutants, our data provide the impetus for future studies on pharmacological treatments aimed at restoring the hydration level and chemical composition of vocal fold surface fluid.

Figure 1

Transepithelial resistance (R_T) in response to both sham challenge and hypertonic challenge over time. Negative ΔR_T values suggest a decrease in resistance from baseline. Error bars represent standard error of the mean.

Figure 2

Representative transmission electron microscopic images (original magnification: ×37,000) of the paracellular pathway following sham (A) and hypertonic (B) challenge. Arrows represent the dilated paracellular pathway.

Figure 3

Length of the paracellular pathway in vocal fold epithelia following sham and hypertonic challenge (*P = 0.02). Shaded area represents the middle 50th quartile; error bars represent the range.

Figure 4

Representative blots of tight junction proteins in vocal fold epithelia following sham and hypertonic challenge.