Vitamin C activation of the biosynthesis of epoxyeicosatrienoic acids

The cardiovascular effects of vitamin C (VitC) could be mediated by epoxyeicosatrienoic acids (EETs). We aimed to study the mechanism of VitC-dependent microsomal formation of cis- and trans-EETs and the regulation of EET levels in rat isolated perfused kidneys and in vivo. VitC biphasically stimulated rat kidney microsomal cis- and trans-EET formation in a ratio of 1:2, involving the participation of lipid hydroperoxides (LOOHs), Fe2+ , and cytochrome P450 (CYP). Levels of LOOHs correlated with microsomal EET production. LOOH stimulation of CYP isoforms resulted in preferred trans- over cis-EET formation from arachidonic acid and was associated with the cleavage of LOOHs, which indicated a CYP peroxy-genase activity. EETs contributed to VitC-induced vasodilator responses in rat isolated perfused kidneys. VitC (1 mg/ml) given in the drinking water for 9 days doubled rat urinary EET excretion, increased plasma levels of EETs, mostly trans-EETs, by 40%, and reduced plasma levels of 20-hydroxyeicosatetraenoic acid. Depletion of VitC in brain cortex and kidney tissues by more than 20- and 50-fold, respectively, in gulonolactone oxidase-knockout mice was associated with mild increases in tissue EETs. These data suggest that LOOHs are a determinant factor for EET formation in vivo in which VitC exerts a key regulatory effect. VitC-activated CYP peroxygenase activity may represent a CYP interaction with lipoxygenases and cyclooxygenases to mediate the cardiovascular effects of VitC via formation of EETs.

大鼠脑微血管内皮细胞应力敏感性钾通道的研究

为探讨脑微血管内皮细胞的电生理学特征 ,研究了脑微血管内皮细胞钾离子通道的应力反应性。 1.建立了开放式切应力作用装置并进行了切应力值的计算 ;2 .培养大鼠脑微血管内皮细胞并种植到 1cm× 1cm玻片上 ,采用 Axonpatch2 0 0 A型膜片钳放大器以及全细胞膜片钳技术记录脑微血管内皮细胞的应力敏感性钾通道。结果表明 :1.1dynes/ cm2剪切应力能激发脑微血管内皮细胞的应力敏感性钾通道 ,该通道电流与钳制电压有良好的相关性。脑血管内皮细胞膜上的各种应力反应与细胞膜上的应力敏感性钾通道相关。