Measurement of stretch-induced loss of alveolar epithelial barrier integrity with a novel in vitro method

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Abstract
Mechanical ventilation with high tidal volumes has been shown to contribute to the formation or worsening of interstitial and alveolar edema. Previously we showed that application of large biaxial deformations in vitro perturbs the concentration and distribution of functional tight junction proteins in alveolar epithelial cells. Using a novel method, we determined that applied epithelial strain increases paracellular permeability in a dose- and rate-dependent manner. Primary rat alveolar epithelial cells were subjected to 12%, 25%, or 37% change in surface area (ΔSA) cyclic equibiaxial stretch for 1 h. Cells were also stretched noncyclically at 25% ΔSA for 1 h. During the experimental period, a fluorescently tagged ouabain derivative was added to the apical fluid. Evidence of binding indicated functional failure of the paracellular transport barrier. The percentage of field area stained was quantified from microscopic images. There was no significant evidence of basolateral fluorescent staining at 12% ΔSA or at 25% ΔSA applied cyclically or statically. However, cyclic stretch at 37% ΔSA resulted in significantly more staining than in unstretched cells ( P < 0.0001) or those stretched at either 12% ( P < 0.0001) or 25% cyclic ( P < 0.0005) or static ( P < 0.05) ΔSA. These results suggest that large cyclic tidal volumes may increase paracellular permeability, potentially resulting in alveolar flooding.

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