Angiotensin II Activates Phosphatidylinositol 3-Kinase in Vascular Smooth Muscle Cells

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Abstract
Phosphatidylinositol 3-kinase (PI3K) is an important component of the signal transduction systems activated by tyrosine kinase receptors. It has not been established, however, whether PI3K is also an essential mediator for G protein–coupled receptors. The potential involvement of PI3K in G protein–linked angiotensin II (Ang II)–dependent signaling was assessed in a primary cell culture system of porcine coronary artery smooth muscle cells (SMCs). Treatment of quiescent SMCs with Ang II (10−5 to 10−8 mol/L) resulted in a dose-dependent activation of PI3K when assayed in vivo and in vitro. The Ang II receptor antagonists losartan and PD123319 were used to establish that Ang II stimulates PI3K through the Ang II type-1 (AT1) receptor. Immunofluorescent microscopy revealed that Ang II (10−6 mol/L) stimulated the translocation of p85, the regulatory subunit of PI3K, from the perinuclear region to distinct foci throughout the cell within 15 minutes. Western blot analysis of p85 subcellular distribution...