Endothelial-smooth muscle interactions in vitro: effects of high pH, flowing medium and extracellular matrix

The interactions of cultured bovine aortic and human umbilical or saphenous vein endothelium with cultured fibroblasts or smooth muscle cells were studied using light microscopy, scanning electron microscopy, and a radioisotope adhesion assay. (1) Resuspended fibroblasts or smooth muscle cells readily 'overgrew' confluent endothelial monolayers under static culture conditions, but not when cultures were exposed to a continuously stirred medium. (2) Exposure of cultured endothelial or smooth muscle cells to a moderately alkaline environment alters the disposition of pericellular concanavalin. A positive extracellular material. This does not affect the initial adhesion of endothelial or smooth muscle cells, but does affect cell spreading. (3) Endothelial adhesion to cultured smooth muscle cells involves both adhesion and spreading. Recently subcultured or rapidly proliferating smooth muscle cells support initial adhesion, but not spreading. Spreading appears to require the establishment of a suitable extracellular matrix, and this is inhibited both by a flowing medium and by an alkaline extracellular environment.