Angiotensin II-induced delayed stimulation of phospholipase C γ1 requires activation of both phosphatidiylinositol 3-kinase γ and tyrosine kinase in vascular myocytes

In vascular smooth muscles, angiotensin II (AII) has been reported to activate phospholipase C (PLC) and phosphatidylinositol 3-kinase (PI3K). We investigated the time-dependent effects of AII on both phosphatidylinositol 3,4,5-trisphosphate (PtdInsP3) and inositol phosphates (InsPs) accumulation in permeabilized microsomes from rat portal vein smooth muscle in comparison with those of noradrenaline (NA). AII stimulated an early production of PtdInsP3 (within 30 s) followed by a delayed production of InsPs (within 3–5 min), in contrast to NA which activated only a fast production of InsPs. The use of pharmacological inhibitors and antibodies raised against the PI3K and PLC isoforms expressed in portal vein smooth muscle showed that AII specifically activated PI3Kγ and that this isoform was involved in the AII-induced stimulation of InsPs accumulation. NA-induced InsPs accumulation depended on PLCβ1 activation whereas AII-induced InsPs accumulation depended on PLCγ1 activation. AII-induced PLCγ1 activation required both tyrosine kinase and PI3Kγ since genistein and tyrphostin B48 (inhibitors of tyrosine kinase), LY294002 and wortmannin (inhibitors of PI3K) and anti-PI3Kγ antibody abolished AII-induced stimulation of InsPs accumulation. Increased tyrosine phosphorylation of PLCγ1 was only detected for long-lasting applications of AII and was suppressed by genistein. These data indicate that activation of both PI3Kγ and tyrosine kinase is a prerequisite for AII-induced stimulation of PLCγ1 in vascular smooth muscle and suggest that the sequential activation of the three enzymes may be responsible for the slow and long-lasting contraction induced by AII.