THE USE OF AUTORADIOGRAPHY AND CYCLOHEXIMIDE TO DETERMINE THE ORIGIN OF ENAMEL PROTEINS IN THE MATURATION AMELOBLASTS OF THE RAT INCISOR

Morphological and cytochemical studies have suggested that maturation ameloblasts participate in protein loss by absorbing and degrading ena mel proteins as the enamel matures. Several immunocytochemical and aut oradiographic studies have suggested other possible explanations for t he presence of enamel matrix proteins in maturation ameloblasts. The w eakness of these autoradiographic studies is the uncontrolled distribu tion of systemically injected radioactive amino acids, making it impos sible to trace the source of the visualized intracellular isotope. Thi s study used a localized technique to control the targets of the appli ed isotope and to identify enamel matrix proteins in the maturation am eloblasts with more confidence about their origin. The amount of label led enamel protein was higher in maturation ameloblasts than transitio nal ameloblasts. When cycloheximide, a protein-synthesis inhibitor, wa s applied, there was no effect on the amount of labelled protein in th e maturation ameloblasts. These findings support the hypothesis that m aturation ameloblasts actively resorb and degrade enamel matrix protei ns during enamel formation in the mandibular incisor of the rat. (C) 1 998 Elsevier Science Ltd. All rights reserved.