Elastin production by cultured calf pulmonary artery endothelial cells

Calf pulmonary artery (CPA) endothelial cells synthesize and secrete soluble elastin when incubated in medium conditioned by arterial smooth muscle cells. Endothelial cell tropoelastin cross‐reacts with antiserum to bovine ligamentum nuchae elastin and comigrates on SDS‐PAGE with tropoelastins from fetal bovine ligamentum nuchae fibroblasts, aortic smooth muscle cells, and ear chondroblasts at an apparent molecular weight of 70,000. Endothelial cells synthesize only one‐third as much elastin as these other cell types, however. Approximately 80% of the elastin synthesized by endothelial cells in confluent culture is released into the culture medium. The remaining 20% remains associated with the cell layer and is readily extractable with dilute acetic acid as un‐cross‐linked, 70,000‐dalton tropoelastin. The addition of β‐aminopro‐pronitrile to culture medium did not alter the ratio of tropoelastin in the medium and cell layer, suggesting that cross‐linking of tropoelastin does not occur in culture. Immunofluorescent staining of confluent endothelial cell cultures with antielastin serum demonstrated elastin occurring as a web‐like network of fine filaments extending throughout the extracellular space. The fibrous elastin was different in organization and distribution from fibers stained with antifibronectin serum, which were localized primarily beneath the cell layer and in regions of cell‐cell contact. Extracellular matrix remaining after solu‐bilization of cellular material with Triton X‐100 stained positive for fibronectin, but not for elastin.