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B. Yektashenas, A.T. Read, C.R. Ethier, M. Johnson; Cationized Ferritin Decoration as a Marker of True Pores in the Inner Wall Endothelium of Schlemm's Canal . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1848.
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It has been argued that not all the pores in the inner wall endothelium of Schlemm’s canal are true, physiological pores, since experimental studies have shown that some pores appear to be artifacts of fixation and/or processing. (IOVS. 1997; 38:1517–1525) In the present study, cationized ferritin (CF) was used as a marker of true pores based on the decorative CF patterns deposited around and over pores before the fixation process.
5 human eyes were obtained within 24 hours of death and perfused with Dulbecco’s phosphate buffer with added glucose (DBG) at a constant pressure of 6 mmHg for about 30 minutes or until a stable baseline facility was reached. Subsequently, the eyes were exchanged with 2 ml of either 0.25 mg/ml or 0.17 mg/ml of CF, concentrations shown to have minimal effect on outflow facility. The eyes were then perfused for approximately 40 minutes with CF. Next, the eyes were exchanged with 2 ml of DBG in order to wash away any unbound CF and perfused for 5 minutes with DBG. Finally, the eyes were exchanged with 2 ml of fixative (2.5% glutaraldehyde and 2% paraformaldehyde) and perfused for 60–180 minutes with fixative. Eyes were then microdissected to expose the inner wall endothelium of Schlemm’s canal and prepared for scanning electron microscopy using standard procedures.
Pores with CF decoration patterns were seen that strongly implicated their involvement in trans–endothelial fluid transport. Three distinct types of pores were identified: flow labeled (CF decoration was seen within the lumen and on the margins of the pore); saturation labeled (a higher density of CF was seen on the pore margins versus the immediately surrounding areas); and unlabeled. The labeled pores were more often intercellular or border pores (B pores) than intracellular pores (I pores). Furthermore, flow labeled B pores were regularly the largest pores observed (≥ 1.3 µm). Finally, numerous unlabeled pores were also seen, and most often these were I pores.
Our data indicates that at least a fraction of the pores located on the inner wall endothelium of Schlemm’s canal are non–artefactual, i.e. involved in fluid transport. Since large intercellular pores tended to be more frequently labeled, it appears that a significant fraction of flow enters Schlemm’s canal via such pores.
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