Changes of the ratio of calcium to phosphate transported into the mineralizing enamel, dentin and bone.

The relative ratios of 45Ca to 32PO4 transported into the developing enamel, dentin and bone were studied after the simultaneous i. v. injection of 45Ca and 32PO4. Additionally, the distribution of calcein, 45Ca and 32PO4 in the freeze-dried sections of the lower incisor and bone of 9 day-old rats and the stainability of these tissues by glyoxal bis (2-hydroxyanil)(GBHA) staining were examined. Although the distribution of calcein fluorescence indicated the presence of an extracellular route of calcium and phosphate ions from capillary to the enamel in the regions of secretory and smooth-ended ameloblast and to the mineralizing areas of dentin and bone, a cellular contribution to the calcium and phosphate transport was also identified. In the enamel, the ratios of 45Ca to 32PO4 transported into the enamel in the maturation stage were cyclically changed and the ratio in the region of ruffle-ended ameloblasts was significantly high. In the dentin, the calcein, which did not enter the cell, was incorporated into the entire mineralizing front uniformly, whereas the labeling intensity of 45Ca was uneven. The labeling intensity of the mineralizing front was increased toward the incisal side, and the ratio of 45Ca to 32PO4 transported to the front also increased. In the metaphysis of tibia, the surface layer of trabeculae adjacent to the hypertrophic cartilage was heavily labeled with 45Ca whereas the calcein was incorporated in almost all the trabeculae, and the ratio of 45Ca to 32PO4 transported to the bone was apparently higher than that of other mineralizing areas. GBHA staining showed that the stainability of the mineral phase in the areas where calcium was transported with a high Ca/PO4 ratio is very weak. In the cell layer, ameloblasts in the maturation stage, odontoblasts in the incisal area and osteoblasts showed relatively intense staining. These results indicate that the ratios of calcium to phosphate transported to the mineralizing enamel, dentin and bone are controlled by changing the cellular activity for calcium transport, and the maturation of the precursor mineral deposits in the stable crystal phase is facilitated by the increase of the activity.