Program in Neuroscience, Department of Neural and Pain Sciences, University of Maryland Baltimore School of Dentistry, 650 West Baltimore Street, Baltimore, MD 21201, USA.
Neuroscience. 2011 Apr 28;180:344-52. doi: 10.1016/j.neuroscience.2011.01.045. Epub 2011 Feb 2.
In this study, we examined whether functional subunits of the ATP-dependent K+ channel (KATP) are expressed in trigeminal ganglia (TG), which contains sensory neurons that innervate oral and facial structures. We also investigated whether direct activation of the KATP effectively attenuates mechanical hypersensitivity in the context of an acute orofacial muscle pain condition. The KATP expression in TG and behavioral studies were conducted in age matched male and female Sprague-Dawley rats. RT-PCR experiments showed that the mRNAs for the inwardly rectifying pore-forming subunits, Kir6.1 and Kir6.2, as well as the regulatory sulfonylurea subunits, SUR1 and SUR2, were reliably detected in TG. Subsequent western blot analysis confirmed that proteins for all four subunits are expressed in TG, and showed that Kir6.2 is expressed at a significantly higher level in male TG compared to that of female rats. This observation was confirmed by the immunohistochemical demonstration of higher percentages of Kir6 positive masseter afferents in female rats. Masseteric injection of capsaicin evokes a time dependent increase in masseter sensitivity to noxious mechanical stimulation. A specific KATP agonist, pinacidil, dose-dependently attenuated the capsaicin-induced mechanical hypersensitivity in male rats. The dose of pinacidil (20 μg) that completely blocked the capsaicin responses in male rats was ineffective in female rats regardless of their estrus phases. Only at the highest dose (300 μg) we used, pinacidil was partially effective in female rats. Similarly, another KATP agonist, diazoxide which targets different KATP subunits also showed sex specific responses in attenuating capsaicin-induced masseter hypersensitivity. These data suggested that sex differences in functional KATP expression in TG may underlie sex specific responses to KATP agonists. The present study provided novel information on sex differences in KATP expression in TG and its contribution under an orofacial muscle pain condition.
在这项研究中,我们研究了三磷酸腺苷(ATP)依赖性钾通道(KATP)的功能亚基是否在三叉神经节(TG)中表达,三叉神经节包含支配口腔和面部结构的感觉神经元。我们还研究了 KATP 的直接激活是否能有效减轻急性口腔颌面肌肉疼痛状态下的机械性高敏感。在年龄匹配的雄性和雌性 Sprague-Dawley 大鼠中进行了 KATP 表达的 TG 和行为研究。RT-PCR 实验表明,内向整流孔形成亚基 Kir6.1 和 Kir6.2 的 mRNAs 以及调节磺酰脲亚基 SUR1 和 SUR2 可在 TG 中可靠检测到。随后的 Western blot 分析证实,所有四个亚基的蛋白均在 TG 中表达,并且表明雄性 TG 中 Kir6.2 的表达水平明显高于雌性大鼠。这一观察结果通过免疫组织化学显示雌性大鼠中 Kir6 阳性咬肌传入纤维的百分比更高得到证实。咬肌注射辣椒素会引起咬肌对有害机械刺激的敏感性随时间增加。特异性 KATP 激动剂,吡那地尔,剂量依赖性地减轻雄性大鼠的辣椒素诱导的机械性高敏感。完全阻断雄性大鼠辣椒素反应的吡那地尔剂量(20 μg)在雌性大鼠中无效,无论其动情期如何。只有在我们使用的最高剂量(300 μg)下,吡那地尔在雌性大鼠中才部分有效。同样,另一种 KATP 激动剂,二氮嗪,靶向不同的 KATP 亚基,在减轻辣椒素诱导的咬肌高敏感方面也表现出性别特异性反应。这些数据表明,TG 中功能性 KATP 表达的性别差异可能是 KATP 激动剂性别特异性反应的基础。本研究提供了关于 TG 中 KATP 表达的性别差异及其在口腔颌面肌肉疼痛状态下的贡献的新信息。