Substrate adhesion of rat hepatocytes. On the role of fibronectin in cell spreading

The spreading behaviour of rat hepatocytes has been investigated. Extensive spreading occurred on substrates made of fibronectin, native collagen fibres, native collagen monomers, and denatured collagen, respectively. An intermediate degree of spreading was observed on substrates made of antibodies directed against the cell surface. The hepatocytes did not show any spreading on substrates made of asialo-ceruloplasmin, concanavalin A or polycationic ferritin, although they readily attached to these substrates. Spreading on denatured collagen and on cell surface antibodies could be inhibited by anti-fibronectin indicating that fibronectin, produced by hepatocytes and immobilized in the substrate, mediated the spreading of cells on these substrates. On the other hand, spreading on native collagen was not inhibited by anti-fibronectin, which suggests that this spreading reaction was not mediated by fibronectin. It was observed that the rate at which hepatocytes spread on collagenous substrates increased with the amount of collagen molecules in the substrate, indicating that spreading of cells is not only triggered by attachment to a proper substrate per se, but depends on the number of adhesion bonds formed by each cell as well.