Abstract
Ionic lanthanum was used to examine the distribution of calcium-binding sites in the condylar cartilages of rats that had been fed on normal and/or vitamin D-deficient rachitogenic diets for 4 weeks. Certain specific changes in the ultrastructure of the cartilage were attributed to the presence of the trivalent cation in the fixation medium. Cartilages from the rachitic animals showed a marked reduction in the quantity of lanthanum deposition on the outer surface of the chondrocytes and in the extracellular matrix. Returning rachitic rats to the control diet resulted in a corresponding return to a normal ultrastructural distribution of lanthanum in the condylar cartilages. No intracellular lanthanum deposits were observed. The results suggest that a vitamin D-dependent calcium-binding component may be an integral part of the chondrocyte plasma membrane structure.