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

Inorganic mercury (Hg²⁺) reduced voltage-gated calcium channel currents irreversibility 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 μM and a Hill coefficient of 1.3 T-currents were blocked with Hg²⁺ in the same concentration range (0.5–2 μM). With increasing Hg²⁺ concentrations a slow membrane current was additionally activated most obviously at concentrations over 2 μM 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 continous decrease of calcium channel currents was seen even with the lowest used concentration of Hg²⁺ (5 μM). 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 μM). 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.