Romero M F, Madhun Z T, Hopfer U, Douglas J G
Department of Medicine, University Hospitals of Cleveland, Case Western Reserve University School of Medicine, Ohio 44106.
Adv Prostaglandin Thromboxane Leukot Res. 1991;21A:205-8.
Several laboratories have documented that angiotensin II (AII) induces natriuresis in proximal tubular epithelium by a mechanism that has as yet not been disclosed. The present studies were designed to test the hypothesis that cytochrome P450-dependent metabolites of arachidonic acid mediate this effect. In cultured rabbit proximal tubule a ketoconazole-sensitive product comigrating with 5,6-epoxy-eicosatrienoic acid (5,6-EET) on reverse phase and normal phase HPLC was stimulated two-fold by AII. We employed cultures of early S1 segments on a modified Ussing chamber as a bioassay to evaluate the effects of AII and 5,6-EET on unidirectional 22Na (apical to basolateral) flux (JNa). AII inhibited JNa, an effect that was abolished by ketoconazole. Furthermore, 5,6-EET decreased JNa in a manner analogous to AII, and the effect was potentiated by inhibition of endogenous 5,6-EET production. Employing the Ca2(+)-sensitive fluorescent probe, Fura 2, we observed a dose-dependent increase in [Ca2+]i with nM to microM 5,6-EET, effects that were abolished by depletion of extracellular Ca2+ and voltage-sensitive Ca-channel blockers. These observations support the hypothesis that 5,6-EET represents the second messenger that mediates AII-induced natriuresis via stimulation of Ca2+ influx through voltage-sensitive channels.
几个实验室已证明，血管紧张素II（AII）通过一种尚未被揭示的机制在近端肾小管上皮细胞中诱导利钠作用。本研究旨在验证花生四烯酸的细胞色素P450依赖性代谢产物介导这种作用的假说。在培养的兔近端肾小管中，一种在反相和正相高效液相色谱上与5,6-环氧-二十碳三烯酸（5,6-EET）共迁移的酮康唑敏感产物，被AII刺激了两倍。我们采用改良的尤斯灌流小室上的早期S1节段培养物作为生物测定法，以评估AII和5,6-EET对单向22Na（从顶端到基底外侧）通量（JNa）的影响。AII抑制JNa，这种作用被酮康唑消除。此外，5,6-EET以类似于AII的方式降低JNa，并且通过抑制内源性5,6-EET的产生，这种作用被增强。使用Ca2+敏感荧光探针Fura 2，我们观察到随着5,6-EET浓度从纳摩尔到微摩尔增加，[Ca2+]i呈剂量依赖性增加，细胞外Ca2+耗竭和电压敏感钙通道阻滞剂可消除这些作用。这些观察结果支持这样的假说，即5,6-EET代表通过刺激电压敏感通道的Ca2+内流来介导AII诱导的利钠作用的第二信使。
