Modulation of sodium currents in rat dorsal root ganglion neurons by sulfur dioxide derivatives

The effect of sulfur dioxide (SO2) derivatives, a common air pollutant and exists in vivo as an equilibrium between bisulfate and sulfite, on tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) sodium channels in cultured post-natal dorsal root ganglion (DRG) neurons were studied using the whole cell configuration of patch-clamp technique. SO2 derivatives on two types of sodium currents were either inhibitory or stimulatory depending on the kinetic parameters tested. At a holding potential of - 80 mV, SO2 derivatives suppressed TTX-S sodium currents when depolarizing potential was negative to - 30 mV and TTX-R sodium currents when negative to - 10 mV but they increased them when the depolarizing potential was positive to - 30 or - 10 mV. SO2 derivatives shifted the conductance-voltage curve for TTX-R sodium currents in the depolarizing direction but had little effect on that for TTX-S sodium currents. The steady-state inactivation curve for TTX-R sodium channel was shifted by SO, derivatives in the depolarizing direction as that for TTX-S sodium channel. SO2 derivatives changed the reversal potential and increased the maximum conductance of two types of sodium channels. SO2 derivatives postponed the activating time and delayed the inactivation Of Sodium currents. The results suggest that SO2 derivatives would increase the excitability of neurons and alter the ion selectivity for two types of sodium Currents. (C) 2004 Elsevier B.V All rights reserved.