Ultrastructural localization of concanavalin A in the perfused rat heart.

Staining of the surface coat of heart capillaries and aorta was achieved by perfusing concanavalin A and phytohemagglutinin coupled to horseradish peroxidase through the rat heart. The binding of these lectins provides evidence for the presence of glycoproteins containing mannose, glucose, and N-acetylgalactosamine residues in the endothelial surface coat of rat aorta and heart capillaries. The binding of concanavalin A to capillary endothelium was further followed with radioautography of 125I-labeled concanavalin A in the in vitro perfused rat heart. Following the shorter time intervals of perfusion more than 80 per cent of labeled concanavalin A was releasable by alpha-methyl-D-mannoside and the radioautographic reaction was confined to the endothelial cell surface. Following 60 minutes of perfusion with concanavalin A there was translocation of part of the lectin to the extravascular space and evidence of endothelial cell swelling. A tentative estimate of the concanavalin A binding sites in capillary endothelium was determined to be approximately 5000 per sq. mum.