Cao Chunhua, Payne Kristie, Lee-Kwon Whaseon, Zhang Zhong, Lim Sun Woo, Hamlyn John, Blaustein Mordecai P, Kwon H Moo, Pallone Thomas L
Department of Medicine, UMMS, Baltimore, MD 21201, USA.
Am J Physiol Renal Physiol. 2009 Jan;296(1):F98-F106. doi: 10.1152/ajprenal.90429.2008. Epub 2008 Oct 22.
Descending vasa recta (DVR) are 15-microm vessels that perfuse the renal medulla. Ouabain has been shown to augment DVR endothelial cytoplasmic Ca(2+) (Ca(2+)) signaling. In this study, we examined the expression of the ouabain-sensitive Na-K-ATPase alpha2 subunit in the rat renal vasculature and tested effects of acute ouabain exposure and chronic ouabain treatment on DVR. Immunostaining with antibodies directed against the alpha2 subunit verified its expression in both DVR pericytes and endothelium. Acute application of ouabain (100 or 500 nM) augmented the DVR nitric oxide generation stimulated by acetylcholine (ACh; 10 microM). At a concentration of 1 mM, ouabain constricted microperfused DVR, whereas at 100 nM, it was without effect. Acute ouabain (100 nM) did not augment constriction by angiotensin II (0.5 or 10 nM), whereas l-nitroarginine methyl ester-induced contraction of DVR was slightly enhanced. Ouabain-hypertensive (OH) rats were generated by chronic ouabain treatment (30 microg.kg(-1).day(-1), 5 wk). The acute endothelial Ca(2+) elevation by ouabain (100 nM) was absent in DVR endothelia of OH rats. The Ca(2+) response to 10 nM ACh was also eliminated, whereas the response to 10 microM ACh was not. The endothelial Ca(2+) response to bradykinin (100 nM) was significantly attenuated. We conclude that endothelial responses may offset the ability of acute ouabain exposure to enhance DVR vasoconstriction. Chronic exposure to ouabain, in vivo, leads to hypertension and DVR endothelial dysfunction, manifested as reduced Ca(2+) responses to both ouabain- and endothelium-dependent vasodilators.
直小血管降支（DVR）是灌注肾髓质的15微米血管。哇巴因已被证明可增强DVR内皮细胞质Ca(2+)（Ca(2+)）信号传导。在本研究中，我们检测了哇巴因敏感的Na-K-ATP酶α2亚基在大鼠肾血管系统中的表达，并测试了急性哇巴因暴露和慢性哇巴因处理对DVR的影响。用针对α2亚基的抗体进行免疫染色证实其在DVR周细胞和内皮细胞中均有表达。急性应用哇巴因（100或500 nM）可增强乙酰胆碱（ACh；10 microM）刺激的DVR一氧化氮生成。在浓度为1 mM时，哇巴因使微灌注的DVR收缩，而在100 nM时则无作用。急性哇巴因（100 nM）不会增强血管紧张素II（0.5或10 nM）引起的收缩，而左旋硝基精氨酸甲酯诱导的DVR收缩略有增强。通过慢性哇巴因处理（30微克·千克(-1)·天(-1)，5周）产生了哇巴因高血压（OH）大鼠。OH大鼠的DVR内皮细胞中不存在哇巴因（100 nM）引起的急性内皮Ca(2+)升高。对10 nM ACh的Ca(2+)反应也被消除，而对10 microM ACh的反应则未被消除。内皮对缓激肽（100 nM）的Ca(2+)反应明显减弱。我们得出结论，内皮反应可能抵消急性哇巴因暴露增强DVR血管收缩的能力。体内长期暴露于哇巴因会导致高血压和DVR内皮功能障碍，表现为对哇巴因和内皮依赖性血管舒张剂的Ca(2+)反应降低。
