Mercury (Hg2+) decreases voltage-gated calcium channel currents in rat DRG and Aplysia neurons.

Inorganic mercury (Hg2+) reduced voltage-gated calcium channel currents irreversibly in two different preparations. In cultured rat dorsal root ganglion (DRG) neurons, studied with the whole cell patch clamp technique, a rapid concentration-dependent decrease in the L/N-type currents to a steady state was observed with an IC50 of 1.1 microM and a Hill coefficient of 1.3. T-currents were blocked with Hg2+ in the same concentration range (0.5-2 microM). With increasing Hg2+ concentrations a slow membrane current was additionally activated, most obviously at concentrations over 2 microM Hg2+. This current was irreversible and might be due to the opening of other (non-specific) ion channels by Hg2+. The current-voltage (I-V) relation of DRG neurons shifted to more positive values, suggesting a binding of Hg2+ to the channel protein and/or modifying its gating properties. In neurons of the abdominal ganglion of Aplysia californica, studied with the two electrode voltage clamp technique, a continuous decrease of calcium channel currents was seen even with the lowest used concentration of Hg2+ (5 microM). A steady state was not reached and the effect was irreversible without any change on resting membrane currents, even with high concentrations (up to 50 microM). No shift of the I-V relation of the calcium channel currents was observed. Effects on voltage-activated calcium channel currents with Hg2+ concentrations such low have not been reported before. We conclude that neurotoxic effects of inorganic mercury could be partially due to the irreversible blockade of voltage-activated calcium channels.