Tao Q F, Hollenberg N K, Price D A, Graves S W
Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, Mass. 02115, USA.
Hypertension. 1997 Mar;29(3):815-21. doi: 10.1161/01.hyp.29.3.815.
We have isolated a labile, specific sodium pump inhibitor or digitalis-like factor from the peritoneal dialysate of volume-expanded renal failure patients whose levels correlated closely with volume status and blood pressure. This study characterizes the inhibitory profile of this agent compared with that of ouabain against the three alpha-isoforms of the sodium pump. We prepared microsomal Na,K-ATPase from rat tissues representing the highest proportion of one of the alpha-isoforms. Both Northern and Western blot analyses confirmed that kidney had predominantly the alpha1-isoform, skeletal muscle the alpha2-isoform, and fetal brain the alpha3-isoform. Ouabain (5 x 10(-6) mol/L) produced little inhibition of kidney Na,K-ATPase (3.4+/-2.0%) but significant inhibition of skeletal muscle (37.2+/-3.7%, P<.001) and fetal brain (38.8+/-3.5%, P<.001) activity. In contrast, the labile digitalis-like factor, causing comparable inhibition of fetal brain Na,K-ATPase activity (33.3+/-4.7%), produced markedly greater inhibition of kidney (42.5+/-5.6%, P<.001) and moderately greater inhibition of skeletal muscle pump activity (57.7+/-6.3%, P<.05). In addition, the labile digitalis-like factor produced a marked concentration-dependent inhibition of the alpha2- and alpha3-isoforms (r=.79, P=.00005). Experiments combining the labile digitalis-like factor and ouabain confirmed that digitalis-like factor, unlike ouabain, was an effective inhibitor of all three isoforms in rat, in particular alpha2. The different pattern of isoform sensitivity displayed by the labile digitalis-like factor and ouabain further differentiates the two agents and raises some interesting possibilities about the functional implications of the endogenous factor.
我们从容量扩张型肾衰竭患者的腹膜透析液中分离出一种不稳定的、特异性的钠泵抑制剂或类洋地黄因子，其水平与容量状态和血压密切相关。本研究将该制剂与哇巴因对钠泵的三种α-亚型的抑制作用进行了比较，以明确其抑制特性。我们从大鼠组织中制备了微粒体Na,K-ATP酶，这些组织中某一种α-亚型占比最高。Northern印迹分析和Western印迹分析均证实，肾脏主要含α1-亚型，骨骼肌含α2-亚型，胎儿脑含α3-亚型。哇巴因（5×10⁻⁶ mol/L）对肾脏Na,K-ATP酶的抑制作用较小（3.4±2.0%），但对骨骼肌（37.2±3.7%，P<0.001）和胎儿脑（38.8±3.5%，P<0.001）的活性有显著抑制作用。相比之下，不稳定的类洋地黄因子对胎儿脑Na,K-ATP酶活性的抑制作用相当（33.3±4.7%），但对肾脏的抑制作用明显更强（42.5±5.6%，P<0.001），对骨骼肌泵活性的抑制作用也稍强（57.7±6.3%，P<0.05）。此外，不稳定的类洋地黄因子对α2-和α3-亚型产生了明显的浓度依赖性抑制作用（r=0.79，P=0.00005）。将不稳定的类洋地黄因子与哇巴因联合进行的实验证实，与哇巴因不同，类洋地黄因子是大鼠所有三种亚型的有效抑制剂，尤其是α2。不稳定的类洋地黄因子和哇巴因所表现出的不同亚型敏感性模式进一步区分了这两种制剂，并引发了一些关于内源性因子功能意义的有趣可能性。
