Activation of c-SRC underlies the differential effects of ouabain and digoxin on Ca2+ signaling in arterial smooth muscle cells

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 Ca2+ entry via Na+/Ca2+ 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 Ca2+ 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 Ca2+ concentration ([Ca2+]cyt) or phenylephrine-induced Ca2+ signals in isolated ASMCs. Expression of transporters in the α2 Na+ pump-NCX1-TRPC6 Ca2+ 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...