Ang II attenuates IGF-1-stimulated Na+, K(+)-ATPase activity via PI3K/Akt pathway in vascular smooth muscle cells

We have investigated the role of phosphatidylinositol 3-kinase (PI3K) and serine/threonine protein kinase B (Akt) in mediating vascular smooth muscle cells (VSMC) sodium pump (Na+, K(+)-ATPase) regulatory interactions between insulin-like growth factor-1 (IGF-1) and angiotensin II (Ang II). Treatment with IGF-1 (100 nM) for 30 min or Ang II (100 nM) for 10 min increased sodium pump activity. Pretreatment with Ang II for 10 min, abolished IGF-1 increased sodium pump activity. Given separately for 6 h, Ang II and IGF-1 stimulated alpha1 mRNA accumulation. Phosphorylation on Ser473 of Akt was increased after treatment with both IGF-1 and Ang II. Pretreatment with 100 nM of PI3K inhibitor Wortmannin (WT) for 30 min decreased: IGF-1 and Ang II-stimulated pump activity, phosphorylation of Akt and PI3K protein expression. Pretreatment with Ang II attenuated IGF-1-stimulated sodium pump activity, phosphorylation of Akt and PI3K protein expression. IGF-1 increased the association between IRS-1 and p85, and Ang II as well as PI3K inhibition decreased this IGF-1 effect. These results suggest that Ang II, which increases pump activity alone, reduces the IGF-1 stimulation of sodium pump activity by attenuating PI3K/Akt signaling. These results implicate PI3K/Akt pathways in Ang II/IGF-1 regulation of the sodium pump in VSMC.