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

Abstract

The effect of sulfur dioxide (SO 2) 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. SO 2 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, SO 2 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. SO 2 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 2 derivatives in the depolarizing direction as that for TTX-S sodium channel. SO 2 derivatives changed the reversal potential and increased the maximum conductance of two types of sodium channels. SO 2 derivatives postponed the activating time and delayed the inactivation of sodium currents. The results suggest that SO 2 derivatives would increase the excitability of neurons and alter the ion selectivity for two types of sodium currents.