Changes in the mode of calcium and phosphate transport during rat incisal enamel formation

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Abstract
The distribution of45Ca,32PO4,22Na, and calcein in the freeze-dried sections of rat lower incisor was examined. Also, the ratio of45Ca to32PO4 transported into the enamel at various developmental stages was studied after the simultaneous injection of45Ca and32PO4. The distribution of calcein fluorescence indicated the presence of an extracellular route from capillary to enamel in the areas of both the secretory and smooth-ended ameloblasts. Autoradiograms showed that the45Ca incorporation into the enamel in the smooth-ended ameloblast region was higher than that into the secretory enamel, and a remarkably high incorporation was observed in the enamel of the apical two-thirds of the ruffle-ended ameloblast region. Although the32P incorporation into the enamel of the smooth- and ruffle-ended ameloblast region was higher than in the secretory enamel, the differences between these two regions were not so evident as that observed in the case of45Ca. The high labeling of45Ca and22Na was observed in the apical two-thirds of the ruffle-ended ameloblasts. The45Ca/32PO4 ratio in the secretory enamel was significantly lower than that in the blood, but in the enamel of the smooth-ended ameloblast region the ratio was not significantly lower. Contrarily, the ratio in the enamel of the ruffle-ended ameloblast region was much higher than that in blood. These results indicate that the mode of transport of these ions into enamel is altered in relation to the morphological changes of the ameloblasts.