Qian Ai-Hua, Liu Xin-Qiu, Yao Wei-Yan, Wang Hong-Yu, Sun Jing, Zhou Lin, Yuan Yao-Zong
Department of Gastroenterology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China.
Am J Gastroenterol. 2009 Aug;104(8):2014-27. doi: 10.1038/ajg.2009.227. Epub 2009 Jun 2.
Irritable bowel syndrome (IBS) is associated with a state of chronic visceral hypersensitivity, but the underlying molecular mechanisms of visceral hyperalgesia remain elusive. This study was designed to examine changes in the excitability and alterations of voltage-gated K+ currents in subpopulations of colonic dorsal root ganglion (DRG) neurons in a rat model of IBS-like visceral hypersensitivity.
The model of IBS-like visceral hypersensitivity was induced by intracolonic infusion of 0.5% acetic acid (AA) in saline from postnatal days 8 -21. Experiments were conducted when rats became adults. DRG neurons innervating the colon were identified by 1,1'-dioleoyl-3,3,3',3-tetramethylindocarbocyanine methanesulfonate (DiI) fluorescence labeling and were immunostained for isolectin B4 (IB4) binding to classify these colonic neurons. Patch-clamp recordings were made from acutely dissociated DiI-labeled DRG neurons, and the expression of K+ channel in L6-S2 DRG was examined by reverse transcription-polymerase chain reaction (RT-PCR) and western blot.
(1) Neonatal AA treatment induced long-lasting visceral hypersensitivity without significant inflammation but with mast cell hyperplasia. (2) Colonic DRG neurons contained IB4-positive and negative neurons with different electrophysiological properties. IB4-positive colonic neurons have longer action potentials (APs) and larger A-type K+ currents (I(A)) than the IB4-negative neurons, and IB4 phenotypic changes of colonic neurons were not involved in the chronic visceral hypersensitivity. (3) Neonatal AA treatment decreased I(A) density and changed the electrophysiological properties of I(A) and I(K) by shifting the steady-state inactivation toward a negative direction in IB4-positive colonic neurons. The excitability of these cells increased. (4) Kv4.3 was downregulated in neonatal AA-treated rats compared with control rats, which suggests a possible mechanism regarding the changes in electrical activity of DRG neurons in these rats.
A new model for chronic visceral hypersensitivity following a diluted AA stimulus in the neonatal period is described. The hypersensitivity may be associated with mast cell hyperplasia in the colon and increased excitability of IB4-positive colonic neurons as a result of suppression of I(A) density and a shift in the inactivation curves of I(A) and I(K) in a hyperpolarizing direction in these cells. This study identifies for the first time a specific molecular mechanism in subpopulations of colonic DRG neurons that underlies chronic visceral hypersensitivity.
肠易激综合征（IBS）与慢性内脏超敏状态相关，但内脏痛觉过敏的潜在分子机制仍不清楚。本研究旨在检测IBS样内脏超敏大鼠模型中结肠背根神经节（DRG）神经元亚群的兴奋性变化以及电压门控钾电流的改变。
从出生后第8天至21天，通过向结肠内注入0.5%醋酸（AA）生理盐水诱导IBS样内脏超敏模型。待大鼠成年后进行实验。通过1,1'-二油酰基-3,3,3',3'-四甲基吲哚羰花青甲磺酸盐（DiI）荧光标记鉴定支配结肠的DRG神经元，并对其进行异凝集素B4（IB4）结合免疫染色以对这些结肠神经元进行分类。对急性分离的DiI标记的DRG神经元进行膜片钳记录，并通过逆转录-聚合酶链反应（RT-PCR）和蛋白质免疫印迹法检测L6-S2 DRG中钾通道的表达。
（1）新生期AA处理诱导了持久的内脏超敏反应，无明显炎症，但有肥大细胞增生。（2）结肠DRG神经元包含具有不同电生理特性的IB4阳性和阴性神经元。IB4阳性结肠神经元的动作电位（AP）更长，A 型钾电流（I(A)）比IB4阴性神经元更大，且结肠神经元的IB4表型变化与慢性内脏超敏反应无关。（3）新生期AA处理降低了IB4阳性结肠神经元的I(A)密度，并通过将稳态失活向负方向移动改变了I(A)和I(K)的电生理特性。这些细胞的兴奋性增加。（4）与对照大鼠相比，新生期AA处理的大鼠中Kv4.3表达下调，这提示了这些大鼠DRG神经元电活动变化的一种可能机制。
描述了一种新生期稀释AA刺激后慢性内脏超敏反应的新模型。超敏反应可能与结肠肥大细胞增生以及IB4阳性结肠神经元兴奋性增加有关，后者是由于这些细胞中I(A)密度受抑制以及I(A)和I(K)失活曲线向超极化方向移动所致。本研究首次确定了结肠DRG神经元亚群中慢性内脏超敏反应潜在的特定分子机制。
