Abstract
Evidence that exogenous hyaluronate (HA) binds to the surface of muscle fibroblast cultures was obtained by incubating confluent fibroblasts with 14C-HA purified from fibroblast cell surfaces. Surface-bound 14C-HA was operationally defined as material resistant to six saline washes and solubilized by brief trypsinization. All of the surface-bound radioactivity remains as authentic HA. Exposure of fibroblasts to 100 μg/ml cold HA caused a nearly 3-fold ‘reduction’ in incorporation of isotopic precursors into glycosaminoglycan (GAG); but when intracellular 14C precursors to GAG were quantitated, the entire ‘reduction’ could be accounted for by decreased precursor uptake. Exposure to exogenous HA altered the distribution of newly synthesized GAG by stimulating an increase in total GAG secreted to the medium at the expense of that bound to the culture surface. Qualitatively, the cell surface ratio of 14C-HA: 14C-sulfated GAG (SGAG) of HA-treated cells is about 2.5 times greater than that of untreated cells and the medium ratio is correspondingly reversed. This is primarily the result of stimulated 14C-SGAG release to the culture medium. Addition of cold HA to prelabeled cultures also stimulates the selective turnover of SGAG from the culture surface. Thus, exposure to HA alters the fibroblast surface by accumulation of exogenous HA as well as by stimulation of SGAG turnover.
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