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  • Title: Inhibition of calcium transport by mercury salts in rat cerebellum and cerebral cortex in vitro.
    Author: Yallapragada PR, Rajanna S, Fail S, Rajanna B.
    Journal: J Appl Toxicol; 1996; 16(4):325-30. PubMed ID: 8854219.
    Abstract:
    The present investigation was initiated to study the differential effects of mercury salts on calcium pump activity of rat cerebellum and cerebral cortex in vitro. The calcium pump activity was studied by assaying calcium-adenosine triphosphatase (Ca(2+)-ATPase) in synaptic plasma membranes (SPMs) and microsomes of cerebellum and cerebral cortex in the presence of different micromolar concentrations of mercury and methylmercury. The 45Ca uptake in microsomes of cerebellum and cerebral cortex was also determined in the presence of both the salts of mercury. The SPMs and microsomes were prepared by differential centrifugation using a sucrose gradient (0.8/1.2 M). The Ca(2+)-ATPase activity was determined by estimating the inorganic phosphate. The 45Ca uptake was measured in microsomes by using 45CaCl2. Calcium-ATPase in SPMs was significantly inhibited by these two mercury salts in a concentration-dependent manner. In cerebellum and cortex, the IC50 values for mercuric chloride were 0.065 and 0.081 microM, respectively, whereas they were 0.354 and 0.384 microM for methylmercury chloride, indicating that mercuric chloride was more potent in inhibiting the plasma membrane Ca2+ extrusion process when compared to methylmercury chloride. As seen in SPMs, Ca(2+)-ATPase and 45Ca uptake in microsomes were also significantly inhibited in both cerebellum and cortex by mercury salts in a concentration-dependent manner, the effect being greater with mercuric chloride. These results indicate that both mercury and methylmercury inhibited the Ca2+ pumps located in SPMs and microsomes differentially, and to some extent the effects were also region specific.
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