Ultrastructural Localization of Calmodulin in Rat Incisor Ameloblasts and Odontoblasts During the Early Stages of Development

¹ Laboratoire d'Histologie, Faculté de Chirurgie Dentaire (Paris V), 1 rue Maurice Arnoux, 92120 Montrouge, France
² Laboratoire de Technologie Appliquée à la Microscopie Electronique (C.N.R.S.), 105 boulevard Raspail, 75006 Paris, France
³ U.E.R. Biomédicale des Saints-Pères, 75270 Paris cédex 06, France

We visualized calmodulin distribution in rat incisor pre-secretory and secretory ameloblasts on ultrathin sections, using Lowicryl K4M embedding, antibody to calmodulin prepared from rabbit antiserum, and colloidal gold. The distribution of gold particles was compared with that observed in post-mitotic and secretory odontoblasts, and we also evaluated the effects of aldehyde fixation and fixation by rapid-freezing freeze-substitution.

Evaluation of gold particles showed enhanced immuno-staining during cell development. More particles were found in the cell bodies of secretory cells than in their processes. There was no difference between tissue fixed with aldehyde and that fixed by cryoprocessing.

Gold particles were present mainly in the rough endoplasmic reticulum and to a lesser extent in the nucleus, cytoplasm, and a few vesicles. Although the odontoblast processes displayed gold particles, the latter were never observed in pre-dentin or dentin. However, no such selective intracellular localization was observed in the ameloblasts, where gold particles were present not only in Tomes' processes but also in the interrod forming enamel, and to a lesser degree inside the forming rods. In the underlying enamel at later stages of mineralization, only background labeling was detected. The extracellular location of an intracellular calcium-binding protein suggests either the non-specific binding of antiserum with some enamel proteins or the release of small fragments of the secretory ameloblasts into the forming enamel.