High‐uptake and low‐uptake forms of proteoglycans secreted by arterial smooth muscle cells

Publisher Website
Google Scholar
Abstract
Cultured arterial smooth muscle cells synthesize and secrete two types of sulfated proteoglycans, designated as proteoglycan A and B, into the culture medium. They are isolated as immunologically distinct monomers with relative molecular masses of 280 × 103 and 180 × 103 and are characterized as chondroitin‐sulfate‐rich (A) and dermatan‐sulfate‐rich (B) proteoglycans. Both proteoglycan A and B were labelled with [35S]sulfate and used for studies of endocytosis. Uptake of proteoglycan B by arterial smooth muscle cells shows saturable kinetics. At saturation (500 μ) one cell may endocytose up to 1.5 × 106 proteoglycan B molecules/h. Proteoglycan A is internalized at a 10‐fold lower rate. No saturation kinetics were observed at high proteoglycan A concentrations (500 μ). Endocytosis of proteoglycan B in the presence of an excess of proteoglycan A and vice versa suggest that proteoglycan A and B do not compete for the same receptor site. Free hyaluronate or chondroitin sulfate do not inhibit the uptake of proteoglycan B or A. The results suggest that proteoglycan B is internalized by arterial smooth muscle cells via a high‐affinity receptor‐mediated process, whereas proteoglycan A is taken up by fluid endocytosis and/or by low‐affinity endocytotic processes.