CALCIFICATION OF CHICK VERTEBRAL CHONDROCYTES GROWN IN AGAROSE GELS -A BIOCHEMICAL AND ULTRASTRUCTURAL-STUDY

Chick embryo vertebral chondrocytes (CHECOV cells) grown in agarose ge ls form spherical colonies containing cells of hypertrophic morphology and a metachromatically staining matrix. Biochemical analysis of thes e cultures resulted in the following findings. (i) Calcification of CH ECOV cultures can be induced by addition of P(i) (at least 1.9 mM) or beta-glycerol phosphate (BGP). (ii) Alkaline phosphatase activity reac hes a maximal value at the time when mineral deposition is initiated. (iii) Added BGP is converted to P(i); maximal production of P(i) occur s at the time of maximal alkaline phosphatase activity. (iv) BGP-suppl emented cultures produce a degree of calcification that corresponds to the amount of BGP conversion to P(i). It can be concluded that P(i) i s rate-limiting for the calcification of chondrocyte cultures. BGP pro motes calcification of these cultures by acting as a substrate for the alkaline phosphatase-mediated production of inorganic phosphate.