Chondroitin sulfate-rich proteoglycans secreted by arterial intima smooth muscle cells appear involved in low density lipoprotein entrapment and modification. Hypothetically, such a process may contribute to atherogenesis. We compared composition and size of those proteoglycans synthesized by proliferating and resting human arterial smooth muscle cells for which low density lipoprotein had affinity. Lipoprotein-binding proteoglycans secreted by proliferating cells were larger than those of resting cells (M(r) = 1.1 x 10(6) versus 0.8 x 10(6). This was primarily caused by increased M(r) of the chondroitin sulfate chains (6 x 10(4) versus 3.5 x 10(4)). The glycosaminoglycan chains of the proteoglycans from both cells were made of more than 90% chondroitin 6-sulfate and chondroitin 4-sulfate in a 6:4 ratio. Affinity chromatography indicated that low density lipoprotein had a higher affinity with the proteoglycans synthesized by proliferating cells than those from resting cells. Measured with gel mobility shift assay, the apparent affinity constant of low density lipoproteins for proteoglycans from proliferating cells was 3-fold higher than that for proteoglycans from resting cells. This increased affinity appeared related to the higher relative proportion of proteoglycans with longer glycosaminoglycan chains secreted by the proliferating cells than those secreted by the resting cells.