Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Am J Physiol Cell Physiol. 2013 Feb 15;304(4):C324-33. doi: 10.1152/ajpcell.00337.2012. Epub 2012 Nov 28.
Cardiotonic steroids (CTS) of the strophanthus and digitalis families have opposing effects on long-term blood pressure (BP). This implies hitherto unrecognized divergent signaling pathways for these CTS. Prolonged ouabain treatment upregulates Ca(2+) entry via Na(+)/Ca(2+) exchanger-1 (NCX1) and TRPC6 gene-encoded receptor-operated channels in mesenteric artery smooth muscle cells (ASMCs) in vivo and in vitro. Here, we test the effects of digoxin on Ca(2+) entry and signaling in ASMC. In contrast to ouabain treatment, the in vivo administration of digoxin (30 μg·kg(-1)·day(-1) for 3 wk) did not raise BP and had no effect on resting cytolic free Ca(2+) concentration (Ca(2+)) or phenylephrine-induced Ca(2+) signals in isolated ASMCs. Expression of transporters in the α2 Na(+) pump-NCX1-TRPC6 Ca(2+) signaling pathway was not altered in arteries from digoxin-treated rats. Upregulated α2 Na(+) pumps and a phosphorylated form of the c-SRC protein kinase (pY419-Src, ~4.5-fold) were observed in ASMCs from rats treated with ouabain but not digoxin. Moreover, in primary cultured ASMCs from normal rats, treatment with digoxin (100 nM, 72 h) did not upregulate NCX1 and TRPC6 but blocked the ouabain-induced upregulation of these transporters. Pretreatment of ASMCs with the c-Src inhibitor PP2 (1 μM; 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine) but not its inactive analog eliminated the effect of ouabain on NCX1 and TRPC6 expression and ATP-induced Ca(2+) entry. Thus, in contrast to ouabain, the interaction of digoxin with α2 Na(+) pumps is unable to activate c-Src phosphorylation and upregulate the downstream NCX1-TRPC6 Ca(2+) signaling pathway in ASMCs. The inability of digoxin to upregulate c-Src may underlie its inability to raise long-term BP.
强心甾类（CTS）的毒毛旋花子苷和毛花苷家族对长期血压（BP）有相反的影响。这意味着这些 CTS 存在迄今尚未被认识到的发散信号通路。在体内和体外，延长哇巴因处理会通过 Na(+)/Ca(2+)交换器-1 (NCX1) 和 TRPC6 基因编码的受体操作通道上调肠系膜动脉平滑肌细胞（ASMC）中的 Ca(2+)内流。在这里，我们测试了地高辛对 ASMC 中 Ca(2+)内流和信号转导的影响。与哇巴因处理相反，地高辛（30 μg·kg(-1)·day(-1) 治疗 3 周）的体内给药并未升高血压，对分离的 ASMC 中静息细胞质游离 Ca(2+)浓度 (Ca(2+)) 或苯肾上腺素诱导的 Ca(2+)信号也没有影响。在来自地高辛处理大鼠的动脉中，转运体在 α2 Na(+)泵-NCX1-TRPC6 Ca(2+)信号通路中的表达没有改变。在哇巴因处理的大鼠的 ASMC 中观察到上调的 α2 Na(+)泵和磷酸化形式的 c-SRC 蛋白激酶（pY419-Src，约 4.5 倍），但在未用地高辛处理的大鼠中未观察到。此外，在来自正常大鼠的原代培养的 ASMC 中，用地高辛（100 nM，72 h）处理不会上调 NCX1 和 TRPC6，但会阻断哇巴因诱导的这些转运体的上调。用 c-SRC 抑制剂 PP2（1 μM；4-氨基-5-（4-氯苯基）-7-（叔丁基）吡唑并[3,4-d]嘧啶）预处理 ASMC，但不是其无活性类似物，可消除哇巴因对 NCX1 和 TRPC6 表达和 ATP 诱导的 Ca(2+)内流的影响。因此，与哇巴因相反，地高辛与 α2 Na(+)泵的相互作用不能激活 c-SRC 磷酸化并上调 ASMC 中的下游 NCX1-TRPC6 Ca(2+)信号通路。地高辛不能上调 c-SRC 可能是其不能升高长期血压的基础。
