INHIBITION OF CALCIUM-TRANSPORT BY MERCURY SALTS IN RAT CEREBELLUM AND CEREBRAL-CORTEX IN-VITRO

The present investigation was initiated to study the differential effe cts of mercury salts on calcium pump activity of rat cerebellum and ce rebral cortex in vitro, The calcium pump activity was studied by assay ing calcium-adenosine triphosphatase (Ca2+-ATPase) in synaptic plasma membranes (SPMs) and microsomes of cerebellum and cerebral cortex in t he presence of different micromolar concentrations of mercury and meth ylmercury, The Ca-45 uptake in microsomes of cerebellum and cerebral c ortex 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 Ca2+-ATPase activity was de termined by estimating the inorganic phosphate, The Ca-45 uptake was m easured in microsomes by using (CaCl2)-Ca-45. Calcium-ATPase in SPMs w as significantly inhibited by these two mercury salts in a concentrati on-dependent manner. In cerebellum and cortex, the Ic,, values for mer curic chloride were 0.065 and 0.081 mu M, respectively, whereas they w ere 0.354 and 0.384 mu M for methylmercury chloride, indicating that m ercuric chloride was more potent in inhibiting the plasma membrane Ca2 + extrusion process when compared to methylmercury chloride. As seen i n SPMs, Ca2+-ATPase and Ca-45 uptake in microsomes were also significa ntly inhibited in both cerebellum and cortex by mercury salts in a con centration-dependent manner, the effect being greater with mercuric ch loride, These results indicate that both mercury and methylmercury inh ibited the Ca2+ pumps located in SPMs and microsomes differentially, a nd to some extent the effects were also region specific.