Sugimoto Kenji, Kissin Igor, Strichartz Gary
Pain Research Center, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham & Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Anesth Analg. 2008 Jul;107(1):318-24. doi: 10.1213/ane.0b013e31816d140a.
Resiniferatoxin (RTX) is a potent agonist of the transient receptor potential vanilloid 1 channel (TRPV1) found in peripheral nociceptors. RTX causes cellular excitation first, followed by a long-lasting refractory state, which has suggested its therapeutic use for pain control. RTX's effect could result from specific actions on TRPV1 channels, but might also arise from previously reported TRPV1-independent effects. We have tested whether exposure to RTX compromises ion channels in a TRPV1-independent manner.
Clonal rat anterior pituitary (GH(3)) cells, loaded with the Ca(+2)-sensitive fluorescent dye (fluo-4), were stimulated with the Na(+) channel activator veratridine (VTD) or directly depolarized by 60 mM K(+) solution. The physiological effects of exposure to RTX were evaluated by stimulated increases of fluorescence from raised intracellular [Ca(2+)].
The presence of 10 microM RTX acutely reduced the median fluorescence changes by VTD and 60 mM K(+) to 45% and 50%, respectively (P = 0.018 and 0.043). Prolonged exposure (24 h) of cells to 10 microM RTX, followed by a 2 h washout, reduced the median fluorescence changes by VTD and 60 mM K(+) to 5.6% and 42% of control changes, respectively (P = 0.027 and 0.011). Cell responses to VTD partially recovered, to 42% of control, after incubation in RTX-free medium for 24 h.
RTX at 10 microM directly and acutely inhibited voltage-dependent Ca(2+) channels, in a TRPV1-independent manner. Prolonged exposure (24 h) to 10 microM RTX inhibited voltage-dependent Na(+) channels in addition to the Ca(2+) channels, in at least a partially reversible manner.
树脂毒素（RTX）是在外周伤害感受器中发现的瞬时受体电位香草酸受体1通道（TRPV1）的强效激动剂。RTX首先引起细胞兴奋，随后是持久的不应期，这提示了其在疼痛控制方面的治疗用途。RTX的作用可能源于对TRPV1通道的特异性作用，但也可能源于先前报道的与TRPV1无关的作用。我们测试了暴露于RTX是否会以与TRPV1无关的方式损害离子通道。
用Ca(+2)敏感荧光染料（fluo-4）加载的克隆大鼠垂体前叶（GH(3)）细胞，用Na(+)通道激活剂藜芦碱（VTD）刺激或直接用60 mM K(+)溶液使其去极化。通过细胞内[Ca(2+)]升高引起的荧光增强来评估暴露于RTX的生理效应。
10 microM RTX的存在使VTD和60 mM K(+)引起的荧光变化中位数分别急剧降低至45%和50%（P = 0.018和0.043）。细胞长时间（24小时）暴露于10 microM RTX，随后冲洗2小时，使VTD和60 mM K(+)引起的荧光变化中位数分别降至对照变化的5.6%和42%（P = 0.027和0.011）。在无RTX培养基中孵育24小时后，细胞对VTD的反应部分恢复至对照的42%。
10 microM的RTX以与TRPV1无关的方式直接急性抑制电压依赖性Ca(2+)通道。长时间（24小时）暴露于10 microM RTX除了抑制Ca(2+)通道外，还至少以部分可逆的方式抑制电压依赖性Na(+)通道。
