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 methylmercur y (CH3HgCl) on voltage-activated calcium channel currents (VACCCs) wer e tested, using the whole cell patch clamp recording technique with cu ltured dorsal root ganglion (DRG) neurons from 2-4 day old rat pups. B oth metal compounds reduced the current irreversibly in a concentratio n dependent fashion, reaching a new (lower) steady state within 3 to 5 min after application. Inorganic mercury was more effective in reduci ng the VACCCs with an IC50 of 7.3 mu M, while the IC50 for methylmercu ry was 2.6 mu M. But the threshold concentrations were below 0.25 mu M for both metal compounds and the calcium channel currents were reduce d by more than 90% with concentrations of 5 mu M and 20 mu M, respecti vely. The Hill coefficient for both dose-response relationships was ca lculated as similar to 1. Calcium channel currents were reduced over t he entire voltage range, but the current-voltage relation shifted to m ore positive potentials in a concentration dependent manner, the effec t being more pronounced with HgCl2 than with CH3HgCl (1 mu M HgCl2; 10 mV shift, 5 mu M CH3HgCl: 5 mV shift). At higher concentrations (grea ter than or equal to 2 mu M for HgCl2 and greater than or equal to 10 mu M for CH3HgCl) an unidentified membrane current was observed. The i norganic mercury caused an inward current, while the organic mercury c ompound generated a biphasic current with a transient inward and a lon g lasting outward component. Our results suggest that mercury compound s affect the electrical properties of neurons and thereby decrease cog nitive and motor performance. (C) 1996 Intox Press, Inc.