The Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, USA.
Am J Physiol Renal Physiol. 2012 Sep;303(5):F632-8. doi: 10.1152/ajprenal.00169.2012. Epub 2012 Jun 13.
Fluid shear stress (FSS) is a critical regulator of cation transport in the collecting duct (CD). High-dietary sodium (Na) consumption increases urine flow, Na excretion, and prostaglandin E(2) (PGE(2)) excretion. We hypothesize that increases in FSS elicited by increasing tubular flow rate induce the release of PGE(2) from renal epithelial cells into the extracellular compartment and regulate ion transport. Media retrieved from CD cells exposed to physiologic levels of FSS reveal several fold higher concentration of PGE(2) compared with static controls. Treatment of CD cells with either cyclooxygenase-1 (COX-1) or COX-2 inhibitors during exposure to FSS limited the increase in PGE(2) concentration to an equal extent, suggesting COX-1 and COX-2 contribute equally to FSS-induced PGE(2) release. Cytosolic phospholipase A2 (cPLA2), the principal enzyme that generates the COX substrate arachidonic acid, is regulated by mitogen-activated protein-kinase-dependent phosphorylation and intracellular Ca(2+) concentration (Ca(2+)), both signaling processes, of which, are activated by FSS. Inhibition of the ERK and p38 pathways reduced PGE(2) release by 53.3 ± 8.4 and 32.6 ± 11.3%, respectively, while antagonizing the JNK pathway had no effect. In addition, chelation of Ca(2+) limited the FSS-mediated increase in PGE(2) concentration by 47.5 ± 7.5% of that observed in untreated sheared cells. Sheared cells expressed greater phospho-cPLA2 protein abundance than static cells; however, COX-2 protein expression was unaffected (P = 0.064) by FSS. In microperfused CDs, COX inhibition enhanced flow-stimulated Na reabsorption and abolished flow-stimulated potassium (K) secretion, but did not affect ion transport at a slow flow rate, implicating that high tubular flow activates autocrine/paracrine PGE(2) release and, in turn, regulates flow-stimulated cation transport. In conclusion, FSS activates cPLA2 to generate PGE(2) that regulates flow-mediated Na and K transport in the native CD. We speculate that dietary sodium intake modulates tubular flow rate to regulate paracrine PGE(2) release and cation transport in the CD.
流体切应力 (FSS) 是调节集合管 (CD) 阳离子转运的关键因素。高钠饮食会增加尿量、钠排泄和前列腺素 E2 (PGE2) 排泄。我们假设，通过增加管腔流量引起的 FSS 增加会诱导肾上皮细胞将 PGE2 释放到细胞外间隙，并调节离子转运。与静态对照相比，暴露于生理水平 FSS 的 CD 细胞中回收的培养基中 PGE2 的浓度高出数倍。在暴露于 FSS 时，用环氧化酶-1 (COX-1) 或 COX-2 抑制剂处理 CD 细胞，将 PGE2 浓度的增加限制在相同程度，表明 COX-1 和 COX-2 同等程度地促进 FSS 诱导的 PGE2 释放。胞质型磷脂酶 A2 (cPLA2) 是生成 COX 底物花生四烯酸的主要酶，受丝裂原活化蛋白激酶依赖性磷酸化和细胞内 Ca2+浓度 ([Ca2+]i) 调节，这两个信号过程都被 FSS 激活。ERK 和 p38 通路的抑制分别使 PGE2 释放减少 53.3 ± 8.4%和 32.6 ± 11.3%，而拮抗 JNK 通路则没有效果。此外，[Ca2+]i 的螯合将 FSS 介导的 PGE2 浓度增加限制在未处理的剪切细胞中观察到的 47.5 ± 7.5%。与静态细胞相比，剪切细胞表达更高的磷酸化 cPLA2 蛋白丰度；然而，FSS 对 COX-2 蛋白表达没有影响 (P = 0.064)。在微灌注的 CDs 中，COX 抑制增强了流量刺激的 Na 重吸收，并消除了流量刺激的钾 (K) 分泌，但在低流量率下不影响离子转运，表明高管状流量激活自分泌/旁分泌 PGE2 释放，并反过来调节流量刺激的阳离子转运。总之，FSS 激活 cPLA2 生成 PGE2，调节天然 CD 中的流量介导的 Na 和 K 转运。我们推测，饮食钠摄入量调节管状流量率以调节 CD 中的旁分泌 PGE2 释放和阳离子转运。
