Abstract
Frozen sections of chicken tissues containing aortic and capillary endothelial cells were immunolabeled with two mouse monoclonal antibodies directed to different epitopes of the chicken integrin beta-chain. Integrin is an integral membrane protein complex that is believed to mediate a transmembrane linkage between the extracellular matrix and the actin cytoskeleton. In immunofluorescence experiments with semi-thin frozen sections, the aortic endothelial cells were labeled for integrin all around their surfaces, whereas capillary endothelial cells of heart and kidney were labeled only on their basal surfaces. At the immunofluorescence level of resolution, the distribution of integrin appeared to be correlated with that of F-actin in double-labeling experiments with NBD-phallacidin. These different distributions of integrin on the two types of endothelial cells were definitively confirmed by immunoelectron microscopic labeling with the monoclonal antibodies on ultra-thin frozen sections. These results therefore indicate that the luminal surfaces, as well as the underlying cytoskeleton of capillary endothelial cells, are significantly different in structure from those of aortic endothelial cells. These differences may reflect the vastly different hemodynamic stress to which the two types of endothelial cells are subjected, and in addition may mediate different adhesion properties of the luminal surfaces of the two cell types.