Dept. of Cellular and Integrative Physiology, Univ. of Nebraska Medical Center, Omaha, 68198-5850, USA.
Am J Physiol Heart Circ Physiol. 2010 Mar;298(3):H945-55. doi: 10.1152/ajpheart.00145.2009. Epub 2009 Dec 31.
Elevated central angiotensin II (ANG II) plays a critical role in the sympathoexcitation of chronic heart failure (CHF) by stimulating upregulated ANG II type 1 receptors (AT(1)R) in the rostral ventrolateral medulla (RVLM). However, the link between enhanced ANG II signaling and alterations in the electrophysiological characteristics of neurons in the RVLM remains unclear. In the present experiments, we screened for potentially altered genes in the medulla of rats with CHF that are directly related to neuronal membrane conductance using the Rat Genome 230 2.0 Array GeneChip. We found that CHF rats exhibited a 2.1-fold reduction in Kv4.3 gene expression, one of the main voltage-gated K(+) channels, in the medulla. Real-time RT-PCR and Western blot analysis confirmed the downregulation of Kv4.3 in the RVLM of CHF rats. In intact animals, we found that microinjection of the voltage-gated potassium channel blocker, 4-aminopyridine, into the RVLM evoked a sympathoexcitation and hypertension in both normal and CHF rats. CHF rats exhibited smaller responses to 4-aminopyridine than did normal rats. Finally, we used a neuronal cell line (CATH.a neurons) to explore the effect of ANG II on Kv4.3 expression and function. We found that ANG II treatment significantly downregulated mRNA and protein expression of Kv4.3 and decreased the A-type K(+) current. Employing this cell line, we also found that the ANG II-induced inhibition of Kv4.3 mRNA expression was attenuated by the superoxide scavenger Tempol and the p38 MAPK inhibitor SB-203580. The effects of ANG II were abolished by the AT(1)R antagonist losartan. We conclude that the sympathoexcitation observed in the CHF state may be due, in part, to an ANG II-induced downregulation of Kv4.3 expression and subsequent decrease in K(+) current, thereby increasing the excitability of neurons in the RVLM. The ANG II-induced inhibition of Kv4.3 mRNA expression was mediated by ANG II-AT(1)R-ROS-p38 MAPK signaling.
中枢血管紧张素 II（ANG II）升高通过刺激延髓头端腹外侧区（RVLM）中上调的血管紧张素 II 型 1 受体（AT(1)R）在慢性心力衰竭（CHF）的交感神经兴奋中起关键作用。然而，增强的 ANG II 信号与 RVLM 神经元电生理特性的改变之间的联系尚不清楚。在本实验中，我们使用 Rat Genome 230 2.0 Array GeneChip 筛选了与神经元膜电导直接相关的 CHF 大鼠延髓中可能改变的基因。我们发现 CHF 大鼠的延髓中 Kv4.3 基因表达降低了 2.1 倍，Kv4.3 是主要的电压门控钾（K(+)）通道之一。实时 RT-PCR 和 Western blot 分析证实了 CHF 大鼠 RVLM 中 Kv4.3 的下调。在完整动物中，我们发现 RVLM 中注射电压门控钾通道阻滞剂 4-氨基吡啶会引起正常和 CHF 大鼠的交感神经兴奋和高血压。与正常大鼠相比，CHF 大鼠对 4-氨基吡啶的反应较小。最后，我们使用神经元细胞系（CATH.a 神经元）来研究 ANG II 对 Kv4.3 表达和功能的影响。我们发现，ANG II 处理显著下调了 Kv4.3 的 mRNA 和蛋白表达，并降低了 A 型 K(+)电流。在该细胞系中，我们还发现，超氧化物清除剂 Tempol 和 p38 MAPK 抑制剂 SB-203580 可减弱 ANG II 诱导的 Kv4.3 mRNA 表达抑制。ANG II 的作用被 AT(1)R 拮抗剂 losartan 所消除。我们得出结论，CHF 状态下观察到的交感神经兴奋可能部分归因于 ANG II 诱导的 Kv4.3 表达下调和随后的 K(+)电流减少，从而增加 RVLM 神经元的兴奋性。ANG II 诱导的 Kv4.3 mRNA 表达抑制是通过 ANG II-AT(1)R-ROS-p38 MAPK 信号传导介导的。
