Molecular analysis of the neuropathic pain state using sns-null mutant mice

背根神经节的感觉神经元至少表达7种电压门控性钠通道α亚基。这些异构体在初级感觉通路中呈局限性分布，可能介导多种具有不同动力学性质的钠电流，引起快、慢或持续的钠电流S。然而，关于哪种异构体对背根节神经元中特定的钠电流起作用，人们知之甚少。我们最近发现了两种类型的持续性神经元：一种是河豚毒素(Ttx)耐药，仅见于小型背根节神经元(Ttx；Ttx-R/Persistent&gt；)；另一种是OTner对河豚毒素敏感，存在于中/大型背根节神经元(I_&lt；TTx-S/Persistent&gt；)。已有数据表明，前者最有可能是由Na_V1.9介导，而后者可能是由Na_V1.6介导。为了证实这些可能性，我们进行了单细胞巢式RT-PCR法结合并行膜片钳记录，并研究了mRNARNA与…之间的相关性在已鉴定的背根节神经元中，I_&lt；Na&gt；的更多表达和表型。在TTX存在的情况下，分离Na_V1.8缺失突变小鼠的小背根节神经元，记录I_&lt；TTX-R/Persistent&gt；。大多数与Na_V1.9转录本相关的小神经元表现为I_&lt；TTX-R/Persistent&gt；，证实介导I_&lt；TTX-R/Persistent&gt；的亚型可能是Na_V1.9。然而，出乎意料的是，Na_V1.9也在相当数量的完全缺乏I_&lt；TTX-R/Persistent&gt；的中/大神经元中明显存在。这些结果表明，I&lt；TTX-R/Persistent&gt；不完全依赖于Na_V1.9转录本的水平。一个有趣的发现是，在幼小鼠的小型DRG神经元中，Na_V1.9转录本通常是缺失的，而在大多数突变的小型DRG神经元中，该转录本是明显的。Na_V1.6转录本在幼鼠和突变小鼠的中/大神经元中均有相当一部分的表达。然而，这些神经元并不一致地表现为I_lt；TTX-S/Persistent&gt；，提示Na_V1.6可能不携带I_lt；TTX-S/Persistent&gt；。较少

Sensory neurons in dorsal root ganglia (DRG) express at least seven isoforms of voltage-gated sodium channel (VGSC) α-subunits. These isoforms show localized distribution within the primary sensory path-way and probably mediate multiple types of sodium currents (I_<Na>) with different kinetic properties, giving rise to fast, slow or persistent I_<Na>s. However, little is known as to which isoform is responsible for a particular I_<Na> in DRG neurons. We have recently identified two types persistent I_<Na>s : one is resistant to tetrodotoxin (TTX) and found exclusively in small DRG neurons (I_<TTX-R/persist>), and the otner is sensitive to TTX and found in medium/large DRG neurons (I_<TTX-S/persist>). Available data suggest that the former is most likely to be mediated by Na_V1.9, while the latter may be mediated by Na_V1.6. To confirm these possibilities, we performed single cell nested RT-PCR combined with concurrent patch clamp recording and investigated the correlation between mRNA … More expression and phenotype of I_<Na> in an identified DRG neuron. I_<TTX-R/persist> was recorded in isolation from small DRG neurons of Na_V1.8-null mutant mice in the presence of TTX. Most of the small neurons, which were associated with Na_V1.9 transcript, manifested I_<TTX-R/persist>, confirming that the isoform mediating I_<TTX-R/persist> is probably Na_V1.9. Unexpectedly, however, Na_V1.9 was evident also in a considerable number of medium/large neurons that were totally devoid of I_<TTX-R/persist>. These results indicate that I_<TTX-R/persist> is not solely dependent on the level of Na_V1.9 transcript. An intriguing finding was that Na_V1.9 transcript was often absent in small DRG neurons from naive mice while the same transcript was evident in most of the small DRG neurons from mutants. Expression of Na_V1.6 transcript was demonstrated in a considerable portion of the medium/large neurons from both naive and mutant mice. However, these neurons did not consistently manifest I_<TTX-S/persist> suggesting that I_<TTX-S/persist> may not be carried by Na_V1.6. Less