Sodium Pump Inhibitors In Blood Pressure Regulation

我们之前的研究表明，哺乳动物组织中存在两种内源性钠泵配体（SPL），瓦巴因样化合物和马里诺蟾素共存。与先前描述的SPL不同，MBG作为钠/ k - atp酶（NKA）的抗瓦巴因α -1异构体的选择性抑制剂，NKA是肾脏、血管平滑肌和成人心肌细胞中的主要钠泵异构体。在过去的一年里，我们继续研究了Dahl盐敏感大鼠（DS）的SPL，其中α -1 NKA突变和SPL的代偿反应是NaCl敏感性高血压的基础。我们首次证明了HPLC纯化的高血压DS内源性MBG免疫反应物质能有效抑制肾钠泵（α -1异构体）而不是α -3 NKA异构体（胎鼠大脑）。此外，体内给药抗DS的MBG抗体可阻断血压升高、利钠反应和与NaCl负荷相关的肾钠泵抑制。因此，MBG符合Koch的假设，即一种假定的利钠激素参与了盐敏感性高血压的发病机制。在DS的NaCl高血压发展过程中，NaCl负荷引起的OLC初始刺激通过血管紧张素II敏感通路触发MBG反应。随后，OLC水平恢复到基线水平，但MBG生成持续增加，并导致持续高盐摄入引起的慢性血压升高。先前，我们已经证明蛋白激酶C （PKC）激活导致NKA对SPL的敏感性增强。我们的研究结果表明，上述增强是由于诱导NKA α -1亚基的调节性磷酸化而发生的。这种PKC诱导的NKA磷酸化特异性针对α -1（相对于α -3） NKA亚型。由于SPL和PKC都与NKA活性相互作用，而且NKA和PKC都参与肥厚性信号传导，我们研究了PKC和MBG对α -1 NKA的调节相互作用是否可能成为Dahl高血压治疗干预的靶点。高盐摄入下DS代偿性左室肥厚（LVH）的发展与左室心肌α -1 NKA、PKC β - ii和δ的上调有关。上调的α -1 NKA对MBG的敏感性增强。直接抑制PKC的降压化合物环汀预处理DS可降低血压和左室重量，改善左室功能。LV α -1 NKA仍然上调，但对MBG的敏感性较低。与此同时，环汀处理可阻止左室肌膜中PKC β - ii和δ的上调。因此，α -1 NKA的内源性配体MBG是Dahl高血压发病的重要因素。PKC对α -1 NKA的磷酸化增强了MBG的作用。因此，SPL、PKC β - ii和δ对心血管组织NKA的调节作用是治疗NaCl敏感性高血压的新靶点。

SUMMARY OF WORK Our previous studies demontrated that two endogenous sodium pump ligands (SPL), ouabain-like compound and marinobufagenin, coexist in mammalian tissues. Unlike previously described SPL, MBG acts as a selective inhibitor of ouabain resistant alpha-1 isoform of Na/K-ATPase (NKA), the main sodium pump isoform in the kidney, vascular smooth muscle and adult myocardiocytes. During the last year, we continued studies of SPL in Dahl salt-sensitive rats (DS), in which the mutation of alpha-1 NKA and compensatory responses of SPL underlie development of NaCl sensitive hypertension. For the first time we have demonstrated that HPLC purified endogenous MBG immunoreactive material from hypertensive DS potently inhibits the renal sodium pump (alpha-1 isoform) rather than alpha-3 NKA isoform (fetal rat brain). Further, in vivo administration of MBG antibody to DS blocked the elevations of blood pressure, natriuretic response and inhibition of renal sodium pump associated with NaCl loading. Thus, MBG fulfils the Koch's postulate for a putative natriuretic hormone involved in the pathogenesis of salt-sensitive hypertension. In the course of development of NaCl hypertension in DS, an initial stimulation of OLC induced by NaCl loading triggers an MBG response via angiotensin II sensitive pathway. The OLC level subsequently returns to baseline, but a sustained increase in MBG production occurs and contributes to the chronic BP elevation induced by a sustained high NaCl intake. Previously, we have shown that protein kinase C (PKC) activation leads to enhanced sensitivity of the NKA to SPL. Our results demonstrate that the above potentiation occurs due to induction of regulatory phosphorylation of the NKA alpha-1 subunit. This PKC induced NKA phosphorylation is specific towards alpha-1 (vs. alpha-3) NKA isoform. Since both SPL and PKC interact on NKA activity, and both NKA and PKC are involved in hypertrophic signaling, we studied whether or not the modulatory interaction of PKC and MBG on alpha-1 NKA may be a target for therapeutic intervention in Dahl hypertension. The development of compensatory left ventricular hypertrophy (LVH) in DS on a high NaCl intake was associated with an upregulation of alpha-1 NKA, and PKC beta-II and delta in LV myocardium. Upregulated alpha-1 NKA exhibited enhanced sensitivity to MBG. Pretreatment of DS with cicletanine, an antihypertensive compound which directly inhibits the PKC, resulted in a decrease in blood pressure and LV weight and improvement of LV performance. LV alpha-1 NKA remained upregulated but exhibited less sensitivity to MBG. In parallel, cicletanine treatment prevented the upregulation of PKC beta-II and delta in LV sarcolemma. Thus, an endogenous ligand of alpha-1 NKA, MBG, is an important factor in pathogenesis of Dahl hypertension. Phosphorylation of alpha-1 NKA by PKC potentiates the effects of MBG. Therefore, a modulatory interaction of SPL and PKC beta-II and delta on NKA in cardiovascular tissues is a novel therapeutic target in NaCl sensitive hypertension.