Localization of metallothionein (MT) and expression of MT isoforms inducedby cadmium in rat dental pulp

We investigated the induction of metallothionein (MT) by cadmium (Cd) in th e dental pulp of rat incisors. Time-course studies of MT mRNA expression af ter single Cd injection were observed by Northern-blot analysis. The isofor m-specific expressions of MT mRNAs (MT-I, MT-II and MT-III) were observed u sing the reverse transcriptase-polymerase chain reaction (RT-PCR) method. B oth MT-I and MT-II mRNA levels increased within 3 h, peaked at 3 h and then decreased. These findings demonstrated that MT-I and MT-II mRNA were rapid ly induced by Cd in dental pulp. MT-III mRNA was constitutively expressed i n rat dental pulp. but the expression level did not change by Cd treatment. The localization of MT protein in Cd-treated rat dental pulp was determine d by immunohistochemical staining using anti-MT antibody against MT-I and M T-II. MT protein was localized in the specific cell type of odontoblasts (s ecretory odontoblasts and resting odontoblasts). In conclusion, it is likel y that stained MT in the immunohistochemical study should be MT-I and/or MT -II. Furthermore, MT-I and/or MT-II in Cd-treated rat dental pulp was local ized in odontoblasts, in which accumulation of Cd were reported. The cell-s pecific synthesis of MT may be associated with its metal storage and detoxi fication role in dental tissues.