AUTHOR=Deng Shi-Yu , Tang Xue-Chun , Chang Yue-Chen , Xu Zhen-Zhen , Chen Qin-Yi , Cao Nan , Kong Liang-Jing-Yuan , Wang Yang , Ma Ke-Tao , Li Li , Si Jun-Qiang 

TITLE=Improving NKCC1 Function Increases the Excitability of DRG Neurons Exacerbating Pain Induced After TRPV1 Activation of Primary Sensory Neurons

JOURNAL=Frontiers in Cellular Neuroscience

VOLUME=Volume 15 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/cellular-neuroscience/articles/10.3389/fncel.2021.665596

DOI=10.3389/fncel.2021.665596

ISSN=1662-5102

ABSTRACT=Our aim was to investigate the effects of the protein expression and the function of sodium, potassium and chloride co-transporter (NKCC1) in the dorsal root ganglion (DRG) after activation of transient receptor potential vanilloid 1 receptor (TRPV1) in capsaicin-induced acute neurogenic inflammatory pain and the possible mechanism of action. Male Sprague Dawley rats were randomly divided into control , capsaicin  and inhibitor groups. The expression and distribution of TRPV1 and NKCC1 in rat DRG were observed by immunofluorescence. Thermal radiation and acetone test were used to detect the pain threshold of heat and cold noxious stimulation in each group. The expression of NKCC1 mRNA, NKCC1 protein and p-NKCC1 in  DRG were detected by PCR and Western blotting (WB). Patch clamp and chloride fluorescent probe were used to observe the changes of GABA activation current and intracellular chloride concentration. After intrathecal injection of PKC Inhibitor (GF109203X) or MEK / ERK inhibitor (U0126), the behavioral changes and the expression of NKCC1 and p-ERK protein in DRG were observed.TRPV1 and NKCC1 were co-expressed in DRG. Compared with control group, the immunofluorescence intensity of NKCC1 and p-NKCC1 in capsaicin group was significantly higher, and the expression of NKCC1 in nuclear membrane was significantly higher than that in control group. The expression of NKCC1 mRNA and protein of NKCC1 and p-NKCC1 in capsaicin group were higher than those in control group.After capsaicin injection,GF109203X inhibited the protein expression of NKCC1 and p-ERK, while U0126 inhibited the protein expression of NKCC1. In the capsaicin group, paw withdrawal thermal latency (WTL) was decreased, while cold withdrawal latency (CWL) was prolonged. Bumetanide, GF109203X, or U0126 could reverse the effect. GABA activation current significantly increased in the DRG cells of the capsaicin group,which could be reversed by bumetanide. The concentration of chloride in the DRG cells of the capsaicin group increased, but decreased after bumetanide, GF109203X, and U0126 were administered. Activation of TRPV1 by exogenous agonists can increase the expression and function of NKCC1 protein in  DRG, which is mediated by activation of PKC/p-ERK signaling pathway. These results suggest that NKCC1 may participate in the inflammatory pain induced by TRPV1