COLLAGEN AND PROTEOGLYCAN PRODUCTION BY BOVINE FETAL AND ADULT CHONDROCYTES UNDER LOW-LEVELS OF CALCIUM AND ZINC IONS

The experiments described herein tested the effects of CaCl2 and ZnCl2 , added at various concentrations in the culture medium, upon the synt hesis of collagen and proteoglycan by adult and fetal (articular, epip hyseal and hypertrophic) bovine chondrocytes maintained in high densit y multilayer cultures. CaCl2 concentrations below 0.5 mM or the additi on of 1-50 mu M ZnCl2 to the medium selectively promoted the productio n of collagen by all four populations of chondrocytes but had no effec t on fibroblasts. Further, these changes had no statistically signific ant effect on the incorporation of S-35-sulfate into macromolecules or on the synthesis of gelatinase A, measured by gelatin zymography. The addition of CaCl2 and ZnCl2 at these concentrations did not result in a change in the relative proportion of non-crosslinked H-3-collagen m olecules (synthesized in the presence of beta-aminopropionitrile) part itioning in the cell layer and medium compartments, and did not apprec iably alter the pattern of collagens synthesized by any of the cell po pulations. The hypertrophic cells synthesized high levels of collagen type X in the presence as well as absence of exogenously added cations . However, CaCl2 at 10 mM caused a marked upregulation of collagen typ e X synthesis by a preparation of chondrocytes derived from the entire growth plate, consistent with the view that calcium at that concentra tion stimulated the differentiation of some of the cells into hypertro phic chondrocytes.