Yang Rui-Hua, Strong Judith A, Zhang Jun-Ming
Pain Research Center, Department of Anesthesiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0531, USA.
Mol Pain. 2009 May 28;5:26. doi: 10.1186/1744-8069-5-26.
Inflammatory processes play important roles in both neuropathic and inflammatory pain states, but the effects of inflammation per se within the sensory ganglia are not well understood. The cytokine growth-related oncogene (GRO/KC; CXCL1) shows strong, rapid upregulation in dorsal root ganglion (DRG) in both nerve injury and inflammatory pain models. We examined the direct effects of GRO/KC on small diameter DRG neurons, which are predominantly nociceptive. Whole cell voltage clamp technique was used to measure voltage-activated potassium (K) currents in acutely cultured adult rat small diameter sensory neurons. Fluorescently labeled isolectin B4 (IB4) was used to classify cells as IB4-positive or IB4-negative.
In IB4-negative neurons, voltage-activated K current densities of both transient and sustained components were increased after overnight incubation with GRO/KC (1.5 nM), without marked changes in voltage dependence or kinetics. The average values for the slow and fast decay time constants at 20 mV were unchanged by GRO/KC. The amplitude of the fast inactivating component increased significantly with no large shifts in the voltage dependence of inactivation. The increase in K currents was completely blocked by co-incubation with protein synthesis inhibitor cycloheximide (CHX) or NF-kappaB inhibitors pyrrolidine dithiocarbamate (PDTC) or quinazoline (6-Amino-4-(4-phenoxypheny lethylamino;QNZ). In contrast, the voltage-activated K current of IB4-positive neurons was unchanged by GRO/KC. GRO/KC incubation caused no significant changes in the expression level of eight selected voltage-gated K channel genes in quantitative PCR analysis.
The results suggest that GRO/KC has important effects in inflammatory processes via its direct actions on sensory neurons, and that activation of NF-kappaB is involved in the GRO/KC-induced enhancement of K currents.
炎症过程在神经性疼痛和炎性疼痛状态中均发挥重要作用，但炎症本身在感觉神经节内的作用尚未完全明确。细胞因子生长相关癌基因（GRO/KC；CXCL1）在神经损伤和炎性疼痛模型的背根神经节（DRG）中均表现出强烈、快速的上调。我们研究了GRO/KC对主要为伤害性感受的小直径DRG神经元的直接作用。采用全细胞电压钳技术测量急性培养的成年大鼠小直径感觉神经元中电压门控钾（K）电流。用荧光标记的异凝集素B4（IB4）将细胞分类为IB4阳性或IB4阴性。
在IB4阴性神经元中，与GRO/KC（1.5 nM）过夜孵育后，瞬时和持续成分的电压门控K电流密度均增加，电压依赖性或动力学无明显变化。GRO/KC对20 mV时慢和快衰减时间常数的平均值无影响。快速失活成分的幅度显著增加，失活的电压依赖性无大的偏移。与蛋白质合成抑制剂环己酰亚胺（CHX）或核因子κB抑制剂吡咯烷二硫代氨基甲酸盐（PDTC）或喹唑啉（6-氨基-4-（4-苯氧基苯基）乙胺；QNZ）共同孵育可完全阻断K电流的增加。相比之下，GRO/KC对IB4阳性神经元的电压门控K电流无影响。定量PCR分析显示，GRO/KC孵育对八个选定的电压门控K通道基因的表达水平无显著影响。
结果表明，GRO/KC通过对感觉神经元的直接作用在炎症过程中具有重要作用，并且核因子κB的激活参与了GRO/KC诱导的K电流增强。
