Changes of Metal Components of Mt-Iii in the Brain of Mt-I, Ii Null Mice Exposed to Mercury Vapor

摘要

Mercury (Hg) vapor is effectively absorbed via inhalation and easily passes through the blood-brain barrier. Therefore, mercury poisoning with primarily central nervous system symptoms occurs. Metallothionein (MT) is a cysteine rich metal-binding protein and plays a protective role in the heavy metal poisoning and it is associated with the metabolism of trace elements. Two MT isoforms, MT-I and MT-II, are coordinately in all mammalian tissues. Whereas MT-III is a brain-specific member of the MT family, binds Zn and Cu physiologically and might have important neurophysiological and neuromodulatory functions. In this study, the influences of Hg vapor exposure on metal component of MT-III in MT-I, II null (Null) mice and 129/Sv (W-type) mice were examined. Null and W-type mice were exposed to Hg vapor or air stream for 2 hr and were sacrificed 24 hr later. Brain was dissected into cerebral cortex, cerebellum, and hippocampus. Metal components of MT-III were analyzed by the size-exclusion HPLC connected with ICP-MS. HPLC/ICP-MS analyses revealed that the levels of the Hg component of MT-III in each brain sections of the Null mice were higher than that of the W-type mice after Hg vapor exposure. While the Zn component of MT-III in the Null mice were lower than that of the W-type. The physiological role of MT-III in the brain might be impaired by exposure of Hg vapor and lack of MT-I and MT-II.