Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea.
Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea; Dental Research Institute and Department of Neurobiology and Physiology, School of Dentistry, Seoul National University, Republic of Korea.
Eur J Pharmacol. 2019 Jul 5;854:320-327. doi: 10.1016/j.ejphar.2019.04.036. Epub 2019 Apr 19.
Alpha 2 (α-) adrenoceptor agonists, such as clonidine or dexmedetomidine, have been found to inhibit hyperpolarization-activated, cyclic nucleotide-modulated (HCN) channels, not only by reducing intracellular cyclic AMP levels but also by directly blocking HCN channels. In this study, we examined the inhibitory effect of guanabenz, a centrally acting α-adrenoceptor agonist with high specificity for α-subtype, on HCN channels in mesencephalic trigeminal nucleus (MTN) neurons which robustly express HCN channels and have been suggested to coexpress α-adrenoceptors. By performing whole-cell patch-clamp recording on MTN neurons in brainstem slices, hyperpolarization-activated inward current (I) was examined during guanabenz treatment. Guanabenz inhibited I in a dose-dependent manner, which was likely to be ZD7288-sensitive HCN current as it did not affect barium-sensitive inward rectifying potassium current. Guanabenz not only inhibited I but also shifted the voltage-dependent activation curve to hyperpolarizing potentials. Interestingly, I inhibition by guanabenz was not reversed by α-adrenoceptor antagonist atipamezole treatment or by intracellular cyclic AMP perfusion, suggesting that the inhibition may not result from α-adrenoceptor signalling pathway but from direct inhibition of HCN channels. Coherent to our electrophysiological results, single-cell RT-PCR revealed that most MTN neurons lack α-adrenoceptor mRNA. Our study demonstrates that guanabenz can directly inhibit HCN channels in addition to its primary role of activating α-adrenoceptors.
α2-肾上腺素受体激动剂，如可乐定或右美托咪定，已被发现可抑制超极化激活、环核苷酸调节（HCN）通道，不仅通过降低细胞内环腺苷酸水平，还通过直接阻断 HCN 通道。在这项研究中，我们检查了胍那苄的抑制作用，胍那苄是一种中枢作用的α-肾上腺素受体激动剂，对α亚型具有高度特异性，对强烈表达 HCN 通道的中脑三叉神经核（MTN）神经元中的 HCN 通道进行了检查，并且已经被建议共同表达α-肾上腺素受体。通过在脑桥切片上进行 MTN 神经元的全细胞膜片钳记录，在胍那苄处理期间检查超极化激活内向电流（I）。胍那苄以剂量依赖性方式抑制 I，这可能是 ZD7288 敏感的 HCN 电流，因为它不影响钡敏感内向整流钾电流。胍那苄不仅抑制 I，而且还将电压依赖性激活曲线移向超极化电位。有趣的是，胍那苄对 I 的抑制作用不能通过 α-肾上腺素受体拮抗剂阿替美唑处理或细胞内环腺苷酸灌流来逆转，这表明抑制作用可能不是来自 α-肾上腺素受体信号通路，而是来自 HCN 通道的直接抑制。与我们的电生理结果一致，单细胞 RT-PCR 显示大多数 MTN 神经元缺乏 α-肾上腺素受体 mRNA。我们的研究表明，胍那苄除了激活 α-肾上腺素受体的主要作用外，还可以直接抑制 HCN 通道。
