The presence of plasma proteins facilitates the uptake of 125I-thrombin by the rabbit thoracic aorta endothelium in vitro.
Various purified proteins, protein derivatives and two polysaccharides were added individually to a physiological medium in order to effect uptake of 125I-thrombin by the rabbit aorta endothelium. Over a wide range of concentration (0.004-40 mg/ml), the presence of either purified rabbit or bovine albumin during thrombin uptake encouraged an increase (70-110%) in 125I-thrombin binding by the endothelium and subendothelium compared to uptake by aorta segments in the absence of added protein. Pretreatment of aorta segments with albumin before incubation with 125I-thrombin in the absence of albumin did not encourage thrombin uptake to the same extent as having 125I-thrombin and albumin together. Purified human transferrin, rabbit IgG, chicken ovalbumin or denatured bovine casein could replace albumin to produce a similar enhancement of thrombin uptake. Replacing active concentrations of albumin by either reduced-carboxymethylated albumin, defatted albumin, plasmin-treated or thermolysin-treated albumin also caused an increase (50-130%) in thrombin binding, whereas replacement by acid-hydrolysed albumin or with polyglutamic acid was either ineffective or even inhibitory. Lysine-modified or arginine-modified albumins caused a small enhancement (14-32%) and no enhancement of thrombin uptake, respectively. Dextran, at low concentration (0.04-0.4 mg/ml) did not influence thrombin uptake, and at higher concentration (4-40 mg/ml) caused a decrease in uptake by both the endothelium and subendothelial layers. Low concentration of dextran sulphate inhibited thrombin uptake to 20-30% of control values. These data express the importance of accompanying protein in the response of the vascular endothelium during binding of thrombin. The possibility that other protein-cell interactions may be similarly influenced by macromolecular solutes is also discussed.
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D001798:Blood Proteins / Q000502:physiology*; D002364:Caseins / Q000494:pharmacology; D002645:Chickens; D003911:Dextrans / Q000494:pharmacology; D004727:Endothelium / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007074:Immunoglobulin G / Q000494:pharmacology; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D008297:Male; D010047:Ovalbumin / Q000494:pharmacology; D011817:Rabbits; D012709:Serum Albumin / Q000494:pharmacology; D013917:Thrombin / Q000378:metabolism*; D013997:Time Factors; D014168:Transferrin / Q000494:pharmacology
D001798:Blood Proteins; D002364:Caseins; D003911:Dextrans; D007074:Immunoglobulin G; D007457:Iodine Radioisotopes; D012709:Serum Albumin; D014168:Transferrin; D010047:Ovalbumin; D013917:Thrombin