Sulfur dioxide derivatives increase a hyperpolarization-activated inward current in dorsal root ganglion neurons

The effect of derivatives of sulfur dioxide (SO2), a common air pollutant, which exists in vivo at equilibrium between bisulfate and sulfite, was studied on hyperpolarization-activated cation current (Ih) in cultured post-natal dorsal root ganglion (DRG) neurons using the whole cell configuration of patch-clamp technique. SO2 derivatives increased Ih current in a dose and voltage-dependent manner. The EC50 value was 25 μM and the Hill coefficient was 1.44. 50 μM SO2 derivatives significantly shifted the activation curve of Ih in the hyperpolarizing direction by 5.5 mV. The reversal potential of Ih was shifted to 5.2 mV in positive direction by 10 μM SO2 derivatives. According to the functional role of Ih, the increase of Ih should result in an enhanced neuronal excitability, which was possibly the basis for neuropathic pain.