Institute for Biomedical Sciences of Pain and Institute for Functional Brain Disorders, Tangdu Hospital, The Fourth Military Medical University, #1 Xinsi Road, Baqiao, Xi'an, 710038, People's Republic of China.
Neuromolecular Med. 2013 Mar;15(1):209-17. doi: 10.1007/s12017-012-8211-0. Epub 2012 Dec 22.
Tetrodotoxin-resistant (TTX-R) sodium channels NaV1.8 and NaV1.9 in dorsal root ganglion (DRG) neurons play important roles in pathological pain. We recently reported that melittin, the major toxin of whole bee venom, induced action potential firings in DRG neurons even in the presence of a high concentration (500 nM) of TTX, indicating the contribution of TTX-R sodium channels. This hypothesis is fully investigated in the present study. After subcutaneous injection of melittin, NaV1.8 and NaV1.9 significantly upregulate mRNA and protein expressions, and related sodium currents also increase. Double immunohistochemical results show that NaV1.8-positive neurons are mainly medium- and small-sized, whereas NaV1.9-positive ones are only small-sized. Antisense oligodeoxynucleotides (AS ODNs) targeting NaV1.8 and NaV1.9 are used to evaluate functional significance of the increased expressions of TTX-R sodium channels. Behavioral tests demonstrate that AS ODN targeting NaV1.9, but not NaV1.8, reverses melittin-induced heat hypersensitivity. Neither NaV1.8 AS ODN nor NaV1.9 AS ODN affects melittin-induced mechanical hypersensitivity. These results provide previously unknown evidence that upregulation of NaV1.9, but not NaV1.8, in small-sized DRG neurons contributes to melittin-induced heat hypersensitivity. Furthermore, melittin-induced biological effect indicates a potential strategy to study properties of TTX-R sodium channels.
河豚毒素抗性（TTX-R）钠离子通道 NaV1.8 和 NaV1.9 在背根神经节（DRG）神经元中在病理性疼痛中发挥重要作用。我们最近报道称，蜂毒中的主要毒素蜂肽即使在高浓度（500 nM）TTX 存在的情况下，也能诱导 DRG 神经元产生动作电位，表明 TTX-R 钠离子通道的贡献。本研究对此假说进行了全面研究。蜂肽皮下注射后，NaV1.8 和 NaV1.9 的 mRNA 和蛋白表达显著上调，相关钠电流也增加。双重免疫组织化学结果表明，NaV1.8 阳性神经元主要为中、小神经元，而 NaV1.9 阳性神经元仅为小神经元。靶向 NaV1.8 和 NaV1.9 的反义寡核苷酸（AS ODN）用于评估 TTX-R 钠离子通道表达增加的功能意义。行为测试表明，靶向 NaV1.9 的 AS ODN 逆转了蜂肽诱导的热敏感，而靶向 NaV1.8 的 AS ODN 则没有。NaV1.8 AS ODN 和 NaV1.9 AS ODN 均不影响蜂肽诱导的机械性敏感。这些结果提供了以前未知的证据，表明小 DRG 神经元中 NaV1.9 的上调而不是 NaV1.8 的上调有助于蜂肽诱导的热敏感。此外，蜂肽诱导的生物学效应表明了一种研究 TTX-R 钠离子通道特性的潜在策略。
