Sulfur dioxide derivatives modulation of high-threshold calcium currents in rat dorsal root ganglion neurons

This study addressed the effect of sulfur dioxide (SO2) derivatives on high-voltage-activated calcium currents (HVA-ICa) in somatic membrane of freshly isolated rat dorsal root ganglion (DRG) neurons by using the whole-cell configuration of patch-clamp technique. High-threshold Ca2+ channels are highly expressed in small dorsal root ganglion neurons. SO2 derivatives increased the amplitudes of calcium currents in a concentration-dependent and voltage-dependent manner. The 50% enhancement concentrations (EC50) of SO2 derivatives on HVA-ICa was about 0.4 μM. In addition, SO2 derivatives significantly shifted the activation and inactivation curve in the depolarizing direction. Parameters for the fit of a Boltzmann equation to mean values for the activation were V1/2 = −17.9 ± 1.3 mV before and −12.5 ± 1.1 mV after application 0.5 μM SO2 derivatives 2 min (P < 0.05). The half inactivation of HVA-ICa was shifted 9.7 mV to positive direction (P < 0.05). Furthermore, SO2 derivatives significantly prolonged the slow constant of inactivation, slowed the fast recovery but markedly accelerated the slow recovery of HVA-ICa from inactivation. From HP of −60 mV 0.5 μM SO2 derivatives increased the amplitude of HVA-ICa with a depolarizing voltage step to −10 mV about 54.0% in small DRG neurons but 33.3% in large DRG neurons. These results indicated a possible correlation between the change of calcium channels and SO2 inhalation toxicity, which might cause periphery neurons abnormal regulation of nociceptive transmission via calcium channels.