The surface of rat arterial smooth muscle cells was characterized with respect to some of its chemical and functional properties. The effects of selective enzymic degradations (hyaluronidase, chondroitinases, heparitinase or neuraminidase) on [35S]sulphate-prelabelled cells and on binding sites for cationized ferritin (CF) were examined to assess the presence and relative importance of individual species of macromolecules on the cell surface. The results indicate that about half of the strongly anionic sites on the cell surface (binding CF at pH 2.0) could be ascribed to sulphate groups of glycosaminoglycans and about half to carboxyl groups of sialic acid residues in glycoproteins and/or glycolipids. Weaker anionic sites (binding CF at pH 7.0) largely originated from carboxyl groups of glycosaminoglycans. Chondroitin sulphate and heparan sulphate were the main glycosaminoglycans. The surface of cells from young animals showed a higher glycosaminoglycan and a lower sialic acid content than that of cells from adult animals. Continuous treatment of the cultures with neuraminidase stimulated serum-induced initiation of DNA synthesis, while treatment with hyaluronidase or heparitinase inhibited it. Addition of hyaluronic acid, heparin or heparan sulphate to the culture medium inhibited initiation of DNA synthesis as well as cell proliferation. The effect was more marked in cultures of cells from young animals than from adults, although the latter cells were found to grow at a higher rate and to higher densities. These results suggest a role for cell-surface and pericellular glycoconjugates in growth regulation. A possible mechanism of action is that these molecules, due to their anionic charge or by steric exclusion, interfere with the binding of platelet-derived growth factor, a highly cationic polypeptide, to its cell-surface receptor.
Properties of ecto-(inoganic) pyrophosphatase of nervous system cells in culture. Activation upon partial release of sialic acid from the cell surface.
