Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.
Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania.
J Neurophysiol. 2019 Sep 1;122(3):1136-1146. doi: 10.1152/jn.00306.2019. Epub 2019 Jul 17.
The internal surface of the urinary bladder is covered by the urothelium, a stratified epithelium that forms an impermeable barrier to urinary solutes. Increased urothelial permeability is thought to contribute to symptom generation in several forms of cystitis by sensitizing bladder afferents. In this report we investigate the physiological mechanisms that mediate bladder afferent hyperexcitability in a rat model of cystitis induced by overexpression in the urothelium of claudin-2 (Cldn2), a tight junction-associated protein upregulated in bladder biopsies from patients with interstitial cystitis/bladder pain syndrome. Patch-clamp studies showed that overexpression of Cldn2 in the urothelium sensitizes a population of isolectin GS-IB4-negative [IB4(-)] bladder sensory neurons with tetrodotoxin-sensitive (TTX-S) action potentials. Gene expression analysis revealed a significant increase in mRNA levels of the delayed-rectifier voltage-gated K channel (K)2.2 and the accessory subunit K9.1 in this population of bladder sensory neurons. Consistent with this finding, K2/K9.1 channel activity was greater in IB4(-) bladder sensory neurons from rats overexpressing Cldn2 in the urothelium than in control counterparts. Likewise, current density of TTX-S voltage-gated Na (Na) channels was greater in sensitized neurons than in control counterparts. Significantly, guangxitoxin-1E (GxTX-1E), a selective blocker of K2 channels, blunted the repetitive firing of sensitized IB4(-) sensory neurons. In summary, our studies indicate that an increase in the activity of TTX-S Na and K2/K9.1 channels mediates repetitive firing of sensitized bladder sensory neurons in rats with increased urothelial permeability. Hyperexcitability of sensitized bladder sensory neurons in a rat model of interstitial cystitis/bladder pain syndrome (IC/BPS) results from increased activity of tetrodotoxin-sensitive voltage-gated Na and delayed-rectifier voltage-gated K (K)2/K9.1 channels. Of major significance, our studies indicate that K2/K9.1 channels play a major role in symptom generation in this model of IC/BPS by maintaining the sustained firing of the sensitized bladder sensory neurons.
膀胱的内表面由尿路上皮覆盖，尿路上皮是一种分层上皮，形成尿液溶质不可渗透的屏障。尿路上皮通透性增加被认为通过使膀胱传入神经敏感而导致几种类型膀胱炎的症状产生。在本报告中，我们研究了在由尿路上皮中紧密连接相关蛋白 Claudin-2（Cldn2）过表达诱导的膀胱炎大鼠模型中调节膀胱传入神经高反应性的生理机制，Claudin-2 在间质性膀胱炎/膀胱疼痛综合征患者的膀胱活检中上调。膜片钳研究表明，尿路上皮中 Cldn2 的过表达使一群异硫氰酸荧光素 B4（IB4）阴性 [IB4（-）] 膀胱感觉神经元对河豚毒素敏感（TTX-S）动作电位敏感。基因表达分析显示，在这群膀胱感觉神经元中，延迟整流电压门控 K 通道（K）2.2 和辅助亚基 K9.1 的 mRNA 水平显著增加。与这一发现一致，在尿路上皮中过表达 Cldn2 的大鼠的 IB4（-）膀胱感觉神经元中，K2/K9.1 通道活性大于对照神经元。同样，敏化神经元中 TTX-S 电压门控 Na（Na）通道的电流密度大于对照神经元。值得注意的是，K2 通道选择性阻断剂 guangxitoxin-1E（GxTX-1E）减弱了敏化的 IB4（-）感觉神经元的重复放电。总之，我们的研究表明，TTX-S Na 和 K2/K9.1 通道活性的增加介导了尿路上皮通透性增加的大鼠中敏化膀胱感觉神经元的重复放电。在尿路上皮通透性增加的大鼠模型中，敏感性膀胱感觉神经元的过度兴奋源自 TTX-S 电压门控 Na 和延迟整流电压门控 K（K）2/K9.1 通道活性的增加。具有重要意义的是，我们的研究表明，K2/K9.1 通道通过维持敏化膀胱感觉神经元的持续放电，在这种间质性膀胱炎/膀胱疼痛综合征模型中发挥主要作用，导致症状产生。
