Ostman Johan A R, Nassar Mohammed A, Wood John N, Baker Mark D
Centre for Neuroscience, Institute of Cell and Molecular Science, Queen Mary University of London, Newark Street, London E1 2AT, UK.
J Physiol. 2008 Feb 15;586(4):1077-87. doi: 10.1113/jphysiol.2007.147942. Epub 2007 Dec 20.
Persistent tetrodotoxin-resistant (TTX-r) sodium currents up-regulated by intracellular GTP have been invoked as the site of action of peripheral inflammatory mediators that lower pain thresholds, and ascribed to the Na(V)1.9 sodium channel. Here we describe the properties of a global knock-out of Na(V)1.9 produced by replacing exons 4 and 5 in SCN11A with a neomycin resistance cassette, deleting the domain 1 voltage sensor and introducing a frameshift mutation. Recordings from small (< 25 microm apparent diameter) sensory neurones indicated that channel loss eliminates a TTX-r persistent current. Intracellular dialysis of GTP-gamma-S did not cause an up-regulation of persistent Na(+) current in Na(V)1.9-null neurones and the concomitant negative shift in voltage-threshold seen in wild-type and heterozygous neurones. Heterologous hNa(V)1.9 expression in Na(V)1.9 knock-out sensory neurones confirms that the human clone can restore the persistent Na(+) current. Taken together, these findings demonstrate that Na(V)1.9 underlies the G-protein pathway-regulated TTX-r persistent Na(+) current in small diameter sensory neurones that may drive spontaneous discharge in nociceptive nerve fibres during inflammation.
细胞内鸟苷三磷酸（GTP）上调的持续性河豚毒素抗性（TTX-r）钠电流，被认为是降低疼痛阈值的外周炎症介质的作用位点，并归因于Na（V）1.9钠通道。在此，我们描述了通过用新霉素抗性盒取代SCN11A中的外显子4和5、删除结构域1电压感受器并引入移码突变而产生的Na（V）1.9整体敲除的特性。对小直径（<25微米表观直径）感觉神经元的记录表明，通道缺失消除了TTX-r持续性电流。在Na（V）1.9基因敲除的神经元中，GTP-γ-S的细胞内透析并未导致持续性钠电流上调，也未出现野生型和杂合子神经元中伴随的电压阈值负向偏移。在Na（V）1.9基因敲除的感觉神经元中异源表达人Na（V）1.9证实，该人类克隆可恢复持续性钠电流。综上所述，这些发现表明，Na（V）1.9是小直径感觉神经元中G蛋白途径调节的TTX-r持续性钠电流的基础，该电流可能在炎症期间驱动伤害性神经纤维的自发放电。
