Shear stress alters pleural mesothelial cell permeability in culture

The sliding motion of the lung against the chest wall creates a shear stress in the pleural space, which can be as high as 60 dyn/cm², depending on the respiration rate. Such shear stresses may affect the mesothelial cells that line the pleural space on the lung (visceral pleura) and chest wall (parietal pleura). When exposed to shear stress (17 dyn/cm²) in a parallel- plate flow chamber for 22 h, rat visceral pleura mesothelial cells were not altered morphologically and did not align in the direction of flow, in contrast to the shape changes observed for bovine aortic endothelial cells. By using mesothelial cells cultured on porous microcarrier beads, we measured the permeability of the cells at different flows in a cell-column chromatography assay. The permeabilities to sodium fluorescein and cyanocobalamin increased from 8.2 ± 1.0 and 7.8 ± 0.7 x 10^-5 cm/s to 22.5 ± 1.2 and 21.8 ± 3.0 x 10^-5 cm/s, respectively, when the flow was increased from 0.9 to 3.5 ml/min (corresponding to average shear stresses of 4.7-18.4 dyn/cm²). The permeabilities returned to baseline values when the flow was reduced. Cytochalasin D stimulated an increase in permeability that was not augmented by a subsequent increase in shear stress. These results suggest that the barrier function of mesothelial cells is responsive to changes in fluid shear stress.