The intracellular uptake and protracted release of exogenous heparins by cultured endothelial cells

Heparins from bovine or porcine sources were fed in media for 48 hrs to cultured porcine aortic and human umbilical vein endothelial cells. Heparin was found in pericellular and cellular fractions after extraction by chemical methods and 125I radiolabelled heparins were recovered when radiolabelled heparin was included in the feed. Even after washing and media changes heparin was detected in media and cell fractions up to 6 days post feeding. Metachromatic vacuoles within cells were demonstrated histologically up to 7 days post feeding after staining with toluidine blue. This is the first report of protracted internalization of exogenous heparin by cultured endothelial cells with concurrent prolonged release of the heparin to the media. This clearly demonstrates that the endothelium plays an important role in the distribution and metabolism of heparin.