Downregulated Kv4.3 expression in the RVLM as a potential mechanism for sympathoexcitation in rats with chronic heart failure.
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.
Gao
Lie
L
Dept. of Cellular and Integrative Physiology, Univ. of Nebraska Medical Center, Omaha, 68198-5850, USA. lgao@unmc.edu
Li
Yulong
Y
Schultz
Harold D
HD
Wang
Wei-Zhong
WZ
Wang
Wei
W
Finch
Marcus
M
Smith
Lynette M
LM
Zucker
Irving H
IH
D000804:Angiotensin II / Q000378:metabolism; D000818:Animals; D001835:Body Weight / Q000502:physiology; D002908:Chronic Disease; D004195:Disease Models, Animal; D015536:Down-Regulation; D006333:Heart Failure / Q000378:metabolism / Q000503:physiopathology*; D006439:Hemodynamics / Q000502:physiology; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D051672:Shal Potassium Channels / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013564:Sympathetic Nervous System / Q000378:metabolism / Q000503:physiopathology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D017382:Reactive Oxygen Species; D044140:Receptor, Angiotensin, Type 1; D051672:Shal Potassium Channels; D000804:Angiotensin II; D048051:p38 Mitogen-Activated Protein Kinases