We investigated the induction of metallothionein (MT) by cadmium (Cd) in the bone tissue of rats. To clarify the cell response to Cd in bone, the isoform-specific expression of MT mRNAs (MT-I and MT-II) was examined by reverse transcriptase-polymerase chain reaction (RT-PCR). Both MT-I and MT-II mRNA levels were increased within 3 h by Cd administration. MT (MT-I/MT-II) localization after single Cd injection were also confirmed by immunohistochemical studies. Notably, MT-positive cells were time-dependently increased, and the positive cells were mainly localized in osteocytes. The cell-specific induction of MT may be associated with Cd accumulation and Cd-induced bone injury in vivo. Furthermore, we also found that MT was consecutively expressed in some osteoclasts of control rats. This finding suggested a new role of osteoclasts in bone metabolism.
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