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C.R. Ethier, A.T. Read, D.W. H. Chan; Shear Stress Effects on Schlemm’s Canal Endothelial Cells . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5025.
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Purpose: Schlemm’s canal endothelial cells are derived from vascular endothelium. Vascular endothelial cells sense and respond to shear stress, the tangential force due to fluid flowing over their apical surface, in numerous ways. These include aligning themselves in the direction of flow, altering their cytoskeletal architecture, and secreting MMPs to remodel the vessel wall and alter vessel calibre. We investigated whether physiologically relevant levels of shear stress might occur in Schlemm’s canal. Methods: Ostensibly normal human eyes were fixed at pressure and Schlemm’s canal was microdissected open so that inner and outer walls could be simultaneously visualized and registered with each other. The relative alignment of opposing (inner wall vs. outer wall) Schlemm’s canal endothelial (SCE) cells was measured as a function of distance from collector channel ostia. The distribution of relative angles between opposing cells was tested using the chi–squared goodness of fit test, with null hypothesis of completely random orientation. A theoretical model of flow in a canal with elliptical cross–section was developed to estimate shear stresses applied to endothelial cells by flowing aqueous humor. Results: Six of nine montages showed alignment between inner and outer wall SCE cells. When the data was pooled for all montages, there was a clear trend towards more aligned cells than non–aligned cells (p < 10–6). This trend became slightly stronger when cells closer to collector channel ostia were considered. The theoretical model indicated that average shear stresses on SCE cells ranged from 2 to 25 dynes/cm2 (comparable to those experienced by vascular endothelial cells) for inner–outer wall spacings of 8 to 2.5 µm, respectively. Conclusions: Inner and outer wall Schlemm’s canal endothelial cells tend to align with one another. The most likely explanation is a direct shear stress effect on these cells, which is consistent with values of shear stress calculated from our model. Shear stress due to aqueous humor flowing within Schlemm’s canal is therefore expected to influence cellular function and may play a role in controlling Schlemm’s canal calibre.
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