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

The effect of derivatives of sulfur dioxide (SO(2)), a common air pollutant, which exists in vivo at equilibrium between bisulfate and sulfite, was studied on hyperpolarization-activated cation current (I(h)) in cultured post-natal dorsal root ganglion (DRG) neurons using the whole cell configuration of patch-clamp technique. SO(2) derivatives increased I(h) current in a dose and voltage-dependent manner. The EC(50) value was 25 microM and the Hill coefficient was 1.44. 50 microM SO(2) derivatives significantly shifted the activation curve of I(h) in the hyperpolarizing direction by 5.5 mV. The reversal potential of I(h) was shifted to 5.2 mV in positive direction by 10 microM SO(2) derivatives. According to the functional role of I(h), the increase of I(h) should result in an enhanced neuronal excitability, which was possibly the basis for neuropathic pain.