1. Lintao Qu¹,
2. Yumei Li²,
3. Xinghua Pan²,
4. Pu Zhang¹,
5. Robert H. LaMotte¹, and
6. Chao Ma¹,³

Abstract

Chronic pain may accompany immune-related disorders with an elevated level of serum IgG immune complex (IgG-IC), but the underlying                        mechanisms are obscure. We previously demonstrated that IgG-IC directly excited a subpopulation of dorsal root ganglion (DRG)                        neurons through the neuronal Fc-gamma receptor I (FcγRI). This might be a mechanism linking IgG-IC to pain and hyperalgesia.                        The purpose of this study was to investigate the signaling pathways and transduction channels activated downstream of IgG-IC                        and FcγRI. In whole-cell recordings, IgG-IC induced a nonselective cation current (I_IC) in the rat DRG neurons, carried by Ca²⁺ and Na⁺. The I_IC was potentiated or attenuated by, respectively, lowering or increasing the intracellular Ca²⁺ buffering capacity, suggesting that this current was regulated by intracellular calcium. Single-cell RT-PCR revealed that                        transient receptor potential canonical 3 (TRPC3) mRNA was always coexpressed with FcγRI mRNA in the same DRG neuron. Moreover,                        ruthenium red (a general TRP channel blocker), BTP2 (a general TRPC channel inhibitor), and pyrazole-3 (a selective TRPC3                        blocker) each potently inhibited the I_IC. Specific knockdown of TRPC3 using small interfering RNA attenuated the IgG-IC-induced Ca²⁺ response and the I_IC. Additionally, the I_IC was blocked by the tyrosine kinase Syk inhibitor OXSI-2, the phospholipase C (PLC) inhibitor neomycin, and either the inositol                        triphosphate (IP₃) receptor antagonist 2-aminoethyldiphenylborinate or heparin. These results indicated that the activation of neuronal FcγRI                        triggers TRPC channels through the Syk–PLC–IP₃ pathway and that TRPC3 is a key molecular target for the excitatory effect of IgG-IC on DRG neurons.