基底外侧Na⁺依赖的HCO₃⁻转运体NBCn1介导大鼠髓袢升支粗段的HCO₃⁻内流。
Basolateral Na+-dependent HCO3- transporter NBCn1-mediated HCO3- influx in rat medullary thick ascending limb.
作者信息
Odgaard Elvin, Jakobsen Jakob K, Frische Sebastian, Praetorius Jeppe, Nielsen Søren, Aalkjaer Christian, Leipziger Jens
机构信息
Institute of Physiology, Univeristy of Aarhus, Denmark.
出版信息
J Physiol. 2004 Feb 15;555(Pt 1):205-18. doi: 10.1113/jphysiol.2003.046474. Epub 2003 Dec 12.
The electroneutral Na(+)-dependent HCO3- transporter NBCn1 is strongly expressed in the basolateral membrane of rat medullary thick ascending limb cells (mTAL) and is up-regulated during NH4(+)-induced metabolic acidosis. Here we used in vitro perfusion and BCECF video-imaging of mTAL tubules to investigate functional localization and regulation of Na(+)-dependent HCO3- influx during NH4(+)-induced metabolic acidosis. Tubule acidification was induced by removing luminal Na+ (DeltapHi: 0.88 +/- 0.11 pH units, n = 10). Subsequently the basolateral perfusion solution was changed to CO2/HCO3- buffer with and without Na+. Basolateral Na(+)-H+ exchange function was inhibited with amiloride. Na(+)-dependent HCO3- influx was determined by calculating initial base flux of Na(+)-mediated re-alkalinization. In untreated animals base flux was 8.4 +/- 0.9 pmol min(-1) mm(-1). A 2.4-fold increase of base flux to 21.8 +/- 3.2 pmol min(-1) mm(-1) was measured in NH4(+)-treated animals (11 days, n = 11). Na(+)-dependent re-alkalinization was significantly larger when compared to control animals (0.38 +/- 0.03 versus 0.22 +/- 0.02 pH units, n = 10). In addition, Na(+)-dependent HCO3- influx was of similar magnitude in chloride-free medium and also up-regulated after NH4+ loading. Na(+)-dependent HCO3- influx was not inhibited by 400 microm DIDS. A strong up-regulation of NBCn1 staining was confirmed in immunolabelling experiments. RT-PCR analysis revealed no evidence for the Na(+)-dependent HCO3- transporter NBC4 or the two Na(+)-dependent CI-/HCO3- exchangers NCBE and NDCBE. These data strongly indicate that rat mTAL tubules functionally express basolateral DIDS-insensitive NBCn1. Function and protein are strongly up-regulated during NH4(+)-induced metabolic acidosis. We suggest that NBCn1-mediated basolateral HCO3- influx is important for basolateral NH3 exit and thus NH4+ excretion by means of setting pHi to a more alkaline value.
电中性的Na(+)-依赖型HCO3-转运体NBCn1在大鼠髓袢升支粗段细胞（mTAL）的基底外侧膜中大量表达，并且在NH4(+)-诱导的代谢性酸中毒期间上调。在此，我们利用mTAL小管的体外灌注和BCECF视频成像技术，研究了NH4(+)-诱导的代谢性酸中毒期间Na(+)-依赖型HCO3-内流的功能定位和调节。通过去除管腔中的Na+诱导小管酸化（ΔpH i：0.88±0.11 pH单位，n = 10）。随后，将基底外侧灌注液更换为含或不含Na+的CO2/HCO3-缓冲液。用氨氯吡咪抑制基底外侧Na(+)-H+交换功能。通过计算Na(+)-介导的再碱化的初始碱通量来确定Na(+)-依赖型HCO3-内流。在未处理的动物中，碱通量为8.4±0.9 pmol min(-1) mm(-1)。在NH4(+)-处理的动物（11天，n = 11）中测得碱通量增加了2.4倍，达到21.8±3.2 pmol min(-1) mm(-1)。与对照动物相比，Na(+)-依赖型再碱化显著更大（0.38±0.03对0.22±0.02 pH单位，n = 10）。此外，在无氯培养基中，Na(+)-依赖型HCO3-内流的幅度相似，并且在NH4+负荷后也上调。400 μM DIDS不抑制Na(+)-依赖型HCO3-内流。免疫标记实验证实了NBCn1染色的强烈上调。RT-PCR分析未发现Na(+)-依赖型HCO3-转运体NBC4或两种Na(+)-依赖型Cl-/HCO3-交换体NCBE和NDCBE的证据。这些数据强烈表明，大鼠mTAL小管在功能上表达基底外侧对DIDS不敏感的NBCn1。在NH4(+)-诱导的代谢性酸中毒期间，功能和蛋白强烈上调。我们认为，NBCn1介导的基底外侧HCO3-内流对于基底外侧NH3的排出很重要，因此通过将pH i设置为更碱性的值来促进NH4+的排泄。
Zotero 插件