Methylmercury-induced augmentation of oxidative metabolism in cerebellar neurons dissociated from the rats: its dependence on intracellular Ca²⁺

Effect of methylmercury chloride on oxidative metabolism of cerebellar neurons dissociated from the rats was examined using 2′,7′-dichlorofluorescin (DCFH) which is oxidized by cellular hydrogen peroxide to be a fluorescent compound (DCF) and fluo-3, an indicator for intracellular Ca²⁺ concentration ([Ca²⁺]i). Methylmercury at 1 μM or less did not affect DCF fluorescence of cerebellar neurons. Further increase in concentration of methylmercury (up to 30 μM) induced changes in DCF fluorescence. Thus, DCF fluorescence was slightly attenuated during 5 min after applying methylmercury to the neurons, indicating a decrease in oxidation of DCFH. Thereafter, DCF fluorescence was time-dependently augmented in continued presence of methylmercury, indicating an increase in DCFH oxidation. Although methylmercury-induced augmentation of DCF fluorescence was greatly suppressed under external Ca²⁺-free condition, it was not the case for methylmercury-induced attenuation of DCF fluorescence. Methylmercury at 3 μM or more dose-dependently increased the [Ca²⁺]i. Results suggest that methylmercury increases intracellular Ca²⁺ in cerebellar neurons, resulting in an increase in formation of reactive oxygen species that may contribute to cell injury.