Uptake of radioactive calcium by hard tissue cells

45Ca was injected into prenatal mice to study the calcium uptake by tooth germ cells. Both dental papillae, containing the odontoblasts, and the enamel organs were found to actively metabolized the labeled calcium. The maximum specific radioactivity occurred at 15 minutes after injection. The subcellular organelles (e.g. mitochondria) of the papillae were more active in metabolizing the labeled calcium whereas a large portion of the radioactivity of the enamel organ was found in a fraction containing the precalcified material. In fetal tooth germs, the rate of incorporation of labeled calcium into the precalcified material was slower than in the postnatal tooth germs since a large portion of the radioactivity remained in the soluble fraction.