Glycosaminoglycan Synthesis by Smooth Muscle Cells Cultured in the Absence and Presence of Ascorbic Acid

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Abstract
Bovine and rat smooth muscle cells secreted more collagen when cultured in the presence of ascorbic acid than in its absence. There was also a marked increase in the amounts of sulfated proteoglycans associated with the extracellular matrix compartment of the culture systems, in the presence of the vitamin. This increase appeared to be a direct effect of ascorbic acid on the synthesis of sulfated proteoglycans and was not simply the result of increased amounts of collagen available for proteoglycan interaction. Cultured cells responded rapidly to the addition of ascorbic acid in terms of the incorporation of radio-labeled sulfate. There was a slower response in the incorporation of radioactive Pro into cross-linked collagen. Deprivation of ascorbic acid after prolonged culture in the presence of the vitamin elicited a rapid fall in the rates of sulfate incorporation into the extracellular matrix compartment. Cells cultured in the presence of both 3-aminopropiononitrile fumarate and ascorbic acid still showed enhanced incorporation of radio-labeled sulfate in spite of the inhibition of protein-lysine 6-oxidase and the impairment of formation of cross-linked collagen matrices. A similar result was obtained using 2,2''-bipyridyl in the presence of ascorbic acid; sulfate incorporation remained high while there was 90% decrease in the amount of collagen deposited into the extracellular matrix compartment. There was a marked fall in the amounts of heparan sulfate synthesized by bovine smooth muscle cells in the presence of ascorbic acid, relative to cells not supplemented. Changes in the amounts of other types of proteoglycans were in the opposite direction, and there was also a general increase in the sulfate content of these molecules in the presence of ascorbic acid.

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