SENSITIVITY OF PLATELET MICROTUBULES TO DISASSEMBLY BY METHYLMERCURY

With the aim of identifying a surrogate marker for the neurotoxic effe cts of methylmercury using a peripheral blood sample, the sensitivity of microtubules in circulating blood cells to depolymerization by meth ylmercury was compared. Methylmercuric chloride was added to samples o f human venous blood or to isolated platelets and lymphocytes (human o r rabbit) suspended in RPMI medium plus 10% fetal calf serum. After 1 h, microtubular networks were visualized by immunolabeling with antibo dy specific for tubulin. The percentage of platelets without visible, intact microtubules and the percentage of viable, unactivated lymphocy tes without microtubules visibly radiating from the centriolar region through the cytoplasm were counted. A concentration-dependent loss of microtubules was observed in both cell types. loss of microtubules was more easily quantitated and was observed at significantly lower conce ntrations in platelets compared to lymphocytes. The IC50 (concentratio n of methylmercuric chloride resulting in dissolution of microtubules in 50% of the cells) was 3.1 mu M in platelets and 7.4 mu M in lymphoc ytes in samples exposed in culture medium without erythrocytes. When m ethylmercury was added to whole blood for 1 h, the IC50 increased to 1 82 mu M in platelets and >700 mu M in lymphocytes, consistent with the known sequestration of methylmercury in erythrocytes. With longer dur ations of exposure, much lower concentrations of methylmercury were ef fective in both cell types. When rabbit lymphocytes and platelets were exposed to methylmercury under culture conditions, IC50s in platelets /lymphocytes were 2.5 mu M/4.8 mu M after 1 h of exposure, 0.77 mu M/1 .12 mu M after 20 h, and 0.51 mu M/0.63 mu M after 70 h. The results o f this study suggest that platelets may be more suitable than lymphocy tes as a cell type in which to monitor in vivo effects of methylmercur y on microtubules.