Organic anion transport during rat enamel formation

Abstract

Abstract Objective The C-terminal end of nascent amelogenin is dissociated immediately after secretion and rapidly re-absorbed by ameloblasts, presumably by endocytosis. The purpose of this study was to test whether organic anion transporters (OATs) are also involved in the re-absorption process of enamel matrix proteins via non-endocytotic pathways. Materials and methods Localization of OAT1, OAT2, and OAT3 in rat tooth germs was examined by immunohistochemistry using specific antibodies. Actual translocation of organic anions through the ameloblast layer was further tested by systemic tracer experiments in rats in which Lucifer Yellow (LY), a fluorescent organic anion, was used as a tracer. Results In rat tooth germs, OAT2 was associated exclusively with the distal cell membranes of secretory ameloblasts where Tomes' processes were developed and disappeared when matrix formation was terminated. On the other hand, OAT1 was absent in secretory ameloblasts and was colocalized with the ruffled border of ruffle-ended ameloblasts in the maturation stage. OAT3 was undetectable in ameloblasts and located instead only in the stratum intermedium cells. Systemic administration of LY resulted in intense labeling of immature enamel and also a transient labeling of the cytosol of secretory ameloblasts immunopositive for OAT2. In the maturation stage, cytosolic labeling of LY was negligible in all cells of the enamel organs, including ameloblasts. Conclusions These data suggest the existence of OATs in rat tooth germs and their possible involvement in matrix re-absorption at least in the secretory stage of amelogenesis.