Endothelial glycocalyx in different flow regions of the trabecular outflow pathway in bovine eyes

Glycocalyx is a hair-like structure covering the endothelium of the aqueous outflow pathway. While trabecular outflow is segmental circumferentially around the eye, regional differences in glycocalyx morphology remain largely unexplored. This study investigated glycocalyx variations in the different structures along the trabecular outflow pathway in high-flow (HF) and low-flow (LF) regions of bovine eyes.

Enucleated bovine eyes (n = 8) were perfused with fluorescein to identify HF and LF regions. The glycocalyx was labeled with Alcian Blue 8GX, and radial wedges from the anterior chamber angles of both HF and LF regions were processed for transmission electron microscopy. Glycocalyx thickness and coverage were quantified using ImageJ and compared between different outflow pathway locations in HF and LF regions. Glycocalyx measurements at intracellular (I-pores) and border pores (B-pores), the percentage of glycocalyx-unfilled pores, as well as the percentage of giant vacuoles (GVs) with and without I-pores with glycocalyx lining the inner membrane were evaluated.

Glycocalyx thickness and coverage did not differ significantly between HF and LF regions. However, thickness progressively increased from the proximal (trabecular meshwork) to the distal (episcleral veins) outflow pathway. In both I-pores and B-pores, the glycocalyx was present near the basal opening, edge, and center of the pores, with thickness increasing toward the center. No significant differences in the percentage of glycocalyx-filled pores were observed between HF and LF regions. However, the percentage of GVs with I-pores exhibiting glycocalyx lining the inner cellular membrane was significantly higher (100%) than that of those without I-pores (16%).

No regional differences were found between HF and LF regions, but glycocalyx thickness progressively increased from the proximal to the distal outflow pathway, potentially reflecting varying shear stress conditions. The significantly higher percentage of GVs with I-pores containing glycocalyx lining the inner cellular membrane compared to those without I-pores suggests a relationship between aqueous outflow dynamics and glycocalyx synthesis. These findings provide a morphological basis for future research on glycocalyx alterations in glaucoma and their impact on outflow resistance.