Distribution in caesium chloride gradients of proteoglycans secreted by bovine aorta smooth muscle cells and study of their aggregation with hyaluronate and cartilage proteoglycan.

Smooth muscle cells from media of bovine aorta were cultured with [35S] sulphate and [3H]glucosamine. The 4 M guanidinium chloride extract of cell layer had a greater proportion of its glycosaminoglycans as hyaluronic acid, heparan sulphate and dermatan sulphate than did medium, which contained relatively more chondroitin sulphate. Fractionation of medium and cell layer extract by caesium chloride density gradient centrifugation, under associative and dissociative conditions, respectively, established that heparan sulphate and dermatan sulphate proteoglycans had lower buoyant densities than chondroitin sulphate proteoglycans. Chromatography on Sepharose CL2B showed that chondroitin sulphate-rich proteoglycan from medium bottom fraction contained no high molecular weight aggregate but underwent partial reaggregation with hyaluronic acid. A slight shift to higher molecular weight occurred if cartilage proteoglycan monomer was added to medium bottom fraction, but if both hyaluronic acid and cartilage proteoglycan monomer were added, a high degree of aggregation took place. These observations could be explained if medium bottom fraction contained a proteoglycan-deficient aggregate with a low molecular weight hyaluronate species. Bottom fraction from cell layer extract showed none of these properties.