Voltage-activated calcium channel currents of rat DRG neurons are reduced by mercuric chloride (HgCl2) and methylmercury (CH3HgCl).

The actions of bath applied mercuric chloride (HgCl2) and methylmercury (CH3HgCl) on voltage-activated calcium channel currents (VACCCs) were tested, using the whole cell patch clamp recording technique with cultured dorsal root ganglion (DRG) neurons from 2-4 day old rat pups. Both metal compounds reduced the current irreversibly in a concentration dependent fashion, reaching a new (lower) steady state within 3 to 5 min after application. Inorganic mercury was more effective in reducing the VACCCs with an IC50 of 1.3 microM, while the IC50 for methylmercury was 2.6 microM. But the threshold concentrations were below 0.25 microM for both metal compounds and the calcium channel currents were reduced by more than 90% with concentrations of 5 microM and 20 microM, respectively. The Hill coefficient for both dose-response relationship was calculated as approximately 1. Calcium channel currents were reduced over the entire voltage range, but the current-voltage relation shifted to more positive potentials in a concentration dependent manner, the effect being more pronounced with HgCl2 than with CH3HgCl (1 microM HgCl2: 10 mV shift, 5 microM CH3HgCl: 5 mV shift). At higher concentrations (> or = 2 microM for HgCl2, and > or = 10 microM for CH3HgCl) an unidentified membrane current was observed. The inorganic mercury caused an inward current, while the organic mercury compound generated a biphasic current with a transient inward and a long lasting outward component. Our results suggest that mercury compounds affect the electrical properties of neurons and thereby decrease cognitive and motor performance.