IMMUNOCYTOCHEMICAL EVIDENCE FOR TRANSENDOTHELIAL TRANSPORT OF ALBUMIN AND FIBRINOGEN IN RAT HEART AND DIAPHRAGM

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Abstract
Location of serum albumin and fibrinogen in the capillary endothelium of rat heart and diaphragm was studied using the pre-embedding immunocytochemical technique. In light microscopy both proteins were found to be present in the interstitial space among muscle fibers. In EM, reaction product indicating the antigenic sites for albumin and fibrinogen was located in basement membranes along the capillary endothelium and muscle cells. In the endothelium plasmalemmal vesicles located in abluminal cytoplasm exhibited positive reaction for both proteins. Control experiments confirmed the specificity of the immunocytochemical reaction. Serum proteins, at least albumin and fibrinogen, are transported across the capillary endothelium by plasmalemmal vesicles.