Healy D P, Jayaraman G, Ashirova O
Department of Pharmacology, Mount Sinai School of Medicine, New York University, New York, NY 10029, USA.
Acta Physiol Scand. 2000 Jan;168(1):233-8. doi: 10.1046/j.1365-201x.2000.00666.x.
Nitric oxide (NO) and dopamine (DA) have similar effects on renal function, with both having natriuretic and diuretic effects mediated by vascular and tubular mechanisms. Renal ischaemia or hypoxia have been shown to influence the activity of both systems. However, it is not known whether there is any crosstalk between the NO and dopaminergic systems in the kidney. Here using the porcine proximal tubule-like renal epithelial LLC-PK1 cell line as a model system, we determined whether exposure of cells to chemical hypoxia altered the steady-state levels of D1A receptor mRNA and whether the changes involved the NO system. Exposure of LLC-PK1 cells to chemical hypoxia resulted in a marked increase in D1A receptor mRNA levels as measured by reverse transcription-polymerase chain reaction (RT-PCR). The increased levels of D1A receptor mRNA following hypoxia were blocked by the NO synthase inhibitors NG-nitro-L-arginine methylester (L-NAME) or NG-monomethyl-L-arginine (L-NMMA). Further evidence that the NO system exerted positive effects on D1A receptor gene expression came from finding that the NO donor sodium nitroprusside, the NO precursor L-arginine and the guanosine 3', 5'-cyclic monophosphate (cyclic GMP) analogue 8-Br-cGMP all increased D1A receptor mRNA levels in LLC-PK1 cells. These results indicate that expression of the D1A receptor in LLC-PK1 cells can be positively regulated by the NO system. Such an interaction between the renal NO and DA systems may contribute to the reported protective effects that NO and DA exert upon the kidney under conditions of ischaemia.
一氧化氮（NO）和多巴胺（DA）对肾功能具有相似的作用，二者均通过血管和肾小管机制发挥利钠和利尿作用。研究表明，肾脏缺血或缺氧会影响这两个系统的活性。然而，尚不清楚肾脏中NO系统和多巴胺能系统之间是否存在相互作用。在此，我们以猪近端小管样肾上皮LLC-PK1细胞系为模型系统，确定细胞暴露于化学性缺氧环境是否会改变D1A受体mRNA的稳态水平，以及这些变化是否涉及NO系统。通过逆转录聚合酶链反应（RT-PCR）检测发现，将LLC-PK1细胞暴露于化学性缺氧环境会导致D1A受体mRNA水平显著升高。缺氧后D1A受体mRNA水平的升高被NO合酶抑制剂NG-硝基-L-精氨酸甲酯（L-NAME）或NG-单甲基-L-精氨酸（L-NMMA）阻断。进一步证明NO系统对D1A受体基因表达具有正向作用的证据来自于以下发现：NO供体硝普钠、NO前体L-精氨酸以及鸟苷3'，5'-环磷酸（环磷酸鸟苷）类似物8-溴环磷酸鸟苷均可增加LLC-PK1细胞中D1A受体mRNA的水平。这些结果表明，LLC-PK1细胞中D1A受体的表达可受到NO系统的正向调节。肾脏NO系统和DA系统之间的这种相互作用可能有助于解释在缺血条件下NO和DA对肾脏所发挥的保护作用。
