Asymmetric distribution of charged domains on the two fronts of the endothelium of iris blood vessels.

The authors have studied the distribution of anionic and cationic sites on both luminal and abluminal endothelial aspects of iridial vessels in Macaca mulatta and Macaca fascicularis. With the animals in general anesthesia, anionic ferritin (AF) and cationic ferritin (CF) were either injected intravenam or perfused at known intraocular pressure (15-20 mmHg) through the anterior chamber. AF introduced intravenam was retained in the vessels' lumen. The tight junctions between the endothelial cells were impermeable and the plasmalemmal vesicles did not transport tracer to the iridial stroma. In contrast, when perfused through the anterior chamber, AF was present in the vessels' lumen. Here again the tight junctions between the endothelial cells were impermeable, but AF was contained within a great number of plasmalemmal vesicles. Iridial vessels were impermeable to CF perfused into the lumen, but a continuous layer of CF particles was found to adhere to the luminal plasma membrane. When perfused through the anterior chamber, CF was bound to the proteoglycans associated with collagen fibrils of the iridial stroma and basal laminae of stromal, pericytic, and endothelial cells but was never found in the vessels' lumen. These results indicate that different electrical charges are associated with the plasmalemmal vesicles on the luminal and abluminal fronts of iridial vessels. The authors suggest that in these vessels a unidirectional vesicular transport is responsible for the selective movement of anionic organic substances from the tissues of the eye to the bloodstream.