Department of Pharmacology, New York Medical College, Valhalla, New York;
Division of Intramural Research, National Institute of Environmental Health Science, Research Triangle Park, North Carolina; and.
Am J Physiol Renal Physiol. 2014 Aug 15;307(4):F453-60. doi: 10.1152/ajprenal.00123.2014. Epub 2014 Jun 25.
Cytochrome P-450, family 2, subfamily c, polypeptide 44 (Cyp2c44) epoxygenase metabolizes arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs) in kidney and vascular tissues. In the present study, we used real-time quantitative PCR techniques to examine the effect of high salt or high K(+) (HK) intake on the expression of Cyp2c44, a major Cyp2c epoxygenase in the mouse kidney. We detected Cyp2c44 in the proximal convoluted tubule, thick ascending limb, distal convoluted tubule (DCT)/connecting tubule (CNT), and collecting duct (CD). A high-salt diet increased the expression of Cyp2c44 in the thick ascending limb and DCT/CNT but not in the proximal convoluted tubule and CD. In contrast, an increase in dietary K(+) intake augmented Cyp2c44 expression only in the DCT/CNT and CD. Neither high salt nor HK intake had a significant effect on the blood pressure (BP) of wild-type mice. However, HK but not high salt intake increased BP in CD-specific, Cyp2c44 conditional knockout (KO) mice. Amiloride, an epithelial Na(+) channel (ENaC) inhibitor, normalized the BP of KO mice fed HK diets, suggesting that lack of Cyp2c44 in the CD enhances ENaC activity and increases Na(+) absorption in KO mice fed HK diets. This notion was supported by metabolic cage experiments demonstrating that renal Na(+) excretion was compromised in KO mice fed HK diets. Also, patch-clamp experiments demonstrated that 11,12-EET, a major Cyp2c44 product, but not AA inhibited ENaC activity in the cortical CD of KO mice. We conclude that Cyp2c44 in the CD is required for preventing the excessive Na(+) absorption induced by HK intake by inhibition of ENaC and facilitating renal Na(+) excretion.
细胞色素 P-450，家族 2，亚家族 c，多肽 44（Cyp2c44）环氧合酶将花生四烯酸（AA）代谢为环氧二十碳三烯酸（EETs）在肾脏和血管组织中。在本研究中，我们使用实时定量 PCR 技术研究了高盐或高钾（HK）摄入对 Cyp2c44 表达的影响，Cyp2c44 是小鼠肾脏中主要的 Cyp2c 环氧合酶。我们在近端曲管、厚升支、远端曲管/连接管（CNT）和集合管（CD）中检测到 Cyp2c44。高盐饮食增加了厚升支和 DCT/CNT 中 Cyp2c44 的表达，但在近端曲管和 CD 中没有增加。相反，饮食中钾（K+）的增加仅增加了 DCT/CNT 和 CD 中 Cyp2c44 的表达。高盐或 HK 摄入均未对野生型小鼠的血压（BP）产生显著影响。然而，HK 但不是高盐摄入增加了 Cyp2c44 条件性敲除（KO）小鼠 CD 特异性的 BP。上皮钠通道（ENaC）抑制剂阿米洛利使 HK 饮食喂养的 KO 小鼠的 BP 正常化，表明 CD 中缺乏 Cyp2c44 增强了 ENaC 活性并增加了 KO 小鼠 HK 饮食中的 Na+吸收。代谢笼实验证明，KO 小鼠 HK 饮食喂养时肾脏 Na+排泄受损，支持了这一观点。此外，膜片钳实验表明，Cyp2c44 的主要产物 11,12-EET 抑制了 KO 小鼠皮质 CD 中的 ENaC 活性，但不是 AA。我们得出结论，CD 中的 Cyp2c44 通过抑制 ENaC 和促进肾脏 Na+排泄来防止 HK 摄入引起的 Na+吸收过度。
