ENDOCYTOSIS BY THE CORNEAL ENDOTHELIUM - I - REGULATION OF BINDING AND TRANSPORT OF HEMEPROTEINS AND PEROXIDASE-CONJUGATED LECTINS ACROSS THE TISSUE

Binding, internalization, and movement of hemeproteins and peroxidase- conjugated lectins across organ cultured rat corneal endothelia has be en investigated. Horseradish peroxidase (HRP) type II, bound to the su rface, was minimally internalized and was easily washed off. In contra st, HRP-VI bound and was rapidly internalized. Reaction product was ob served in vesicles, endosomes, multivesicular bodies, and extended alo ng the length of the intercellular space (ICS) to Descemet's membrane. Studies at 4 degrees C indicated HRP-VI bound uni formly along the su rface in a punctate fashion. Exposure to polylysine or mannose signifi cantly decreased uptake. Other tracers such as HRP-VIII, -IX, catalase , and microperoxidase exhibited limited uptake by the tissue. However, endothelia vigorously internalized soybean agglutinin (SBA)-HRP, and reaction product was found intracellularly and within the ICS at the c ell/Descemet's membrane interface. Internalization and the appearance of SBA-HRP within the ICS was diminished following polylysine or manno se treatment. Experiments at 4 degrees C indicated that SBA-HRP bindin g and uptake were temperature sensitive. Wheat germ agglutinin (WGA)-H RP was also strongly endocytosed and reaction product was visualized w ithin vesicles, endosomes, and multivesicular bodies. Although WGA-HRP reaction product was observed within the ICS, none was detected at th e level of Descemet's membrane. The WGA competitive sugar N-acetyl-D-g lucosamine, reduced endocytosis, whereas exposure to unlabeled WGA and mannose together reduced uptake. These results indicate endothelia ex hibit differential uptake of various hemeproteins and lectins which is dependent on charge, mannose receptors, and appropriate surface sugar s.