Fibroblast adhesion on collagen substrata in the presence and absence of plasma fibronectin

We have used scanning electron microscopy and transmission electron microscopy to compare the initial adhesion of baby hamster kidney (BHK) cells and early passage human skin fibroblasts on glass, dried collagen, and hydrated collagen substrata. On glass or dried collagen substrata, BHK cell spreading required fibronectin and the cells were extensively flattened, with broad lamellipodia. In marked contrast, BHK cell spreading on hydrated collagen substrata did not require fibronectin and the cell bodies tended to be rounded, with one or several large filipodia. These filipodia generally penetrated into collagen lattice where they interwove with the collagen fibrils. Proteolysis of the collagen was not evident. In the presence of fibronectin, the morphology of BHK cell spreading on hydrated collagen substrata was similar, except that there was an increase in the number of cells that spread with lamellipodia that did not penetrate the collagen lattice. Human fibroblasts also demonstrated marked differences in cell spreading on glass or dried collagen compared to hydrated collagen substrata. Spreading was characterized by lamellipodia on glass or dried collagen but by multiple filipodia on hydrated collagen. In the latter case, the filipodia penetrated just beneath the surface of the collagen lattice. Added fibronectin was not required for spreading on human fibroblasts on any of the substrata and the presence of added fibronectin had no effect on cell morphology. Finally, the human fibroblasts were observed to form adhesion plaques in some cases where the fibroblasts made close contacts with individual collagen fibrils. The results are discussed in terms of connective tissue organization.