Peripheral inflammation suppresses inward rectifying potassium currents of satellite glial cells in the trigeminal ganglia

Previous studies indicate that silencing Kir4.1, a specific inward rectifying K+ (Kir) channel subunit, in sensory ganglionic satellite glial cells (SGCs) induces behavioral hyperalgesia. However, the function of Kir4.1 channels in SGCs in vivo under pathophysiological conditions remains to be determined. The aim of the present study was to examine whether peripheral inflammation in anesthetized rats alters the SGC Kir4.1 current using in vivo patch clamp and immunohistochemical techniques. Inflammation was induced by injection of complete Freund's adjuvant into the whisker pad. The threshold of escape from mechanical stimulation applied to the orofacial area in inflamed rats was significantly lower than in naive rats. The mean percentage of small/medium diameter trigeminal ganglion (TRG) neurons encircled by Kir4.1-immunoreactive SGCs in inflamed rats was also significantly lower than in naive rats. In vivo whole-cell recordings were made using SGCs in the trigeminal ganglia (TRGs). Increasing extracellular K+ concentrations resulted in significantly smaller potentiation of the mean peak amplitude of the Kir current in inflamed compared with naive rats. In addition, the density of the Ba2+-sensitive Kir current associated with small-diameter TRG neurons was significantly lower in inflamed rats compared with naive rats. Mean membrane potential in inflamed rats was more depolarized than in naive rats. These results suggest that inflammation could suppress Kir4.1 currents of SGCs in the TRGs and that this impairment of glial potassium homeostasis in the TRGs contributes to trigeminal pain. Therefore, the Kir4.1 channel in SGCs may be a new molecular target for the treatment of trigeminal inflammatory pain. (C) 2011 International Association for the Study of Pain. Published by Elsevier B. V. All rights reserved.