Angiotensin II-induced delayed stimulation of phospholipase C ?1 requires activation of both phosphatidiylinositol 3-kinase ? and tyrosine kinase in vascular myocytes

Abstract

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 PI3Kδ 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 PLCδ1 activation required both tyrosine kinase and PI3Kδ since genistein and tyrphostin B48 (inhibitors of tyrosine kinase), LY294002 and wortmannin (inhibitors of PI3K) and anti-PI3Kδ antibody abolished AII-induced stimulation of InsPs accumulation. Increased tyrosine phosphorylation of PLCβ1 was only detected for long-lasting applications of AII and was suppressed by genistein. These data indicate that activation of both PI3Kβ and tyrosine kinase is a prerequisite for AII-induced stimulation of PLCβ1 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.

Role of Phosphatidylinositol 3-Kinase (PI3K), Mitogen-Activated Protein Kinase (MAPK), and Protein Kinase C (PKC) in Calcium Signaling Pathways Linked to the α1-Adrenoceptor in Resistance Arteries

“…In the present study, pharmacological inhibition of PI3K moderately reduced both Ca 2+ entry and vasoconstriction elicited by PE in resistance arteries, without affecting the relationship Ca 2+ -tension for the α 1 -adrenergic agonist indicative of changes in Ca 2+ sensitization. These findings are consistent with earlier studies involving PI3K activation in the transduction pathways for the angiotensin II (AII)-induced Ca 2+ responses and contraction in VSM (Le Blanc et al, 2004; Rakotoarisoa et al, 2006). In vascular myocytes, PI3Kγ isoform was initially shown to mediate AII-induced activation of L-type voltage-dependent Ca 2+ currents, to increase [Ca 2+ ] i and elicit contraction (Quignard et al, 2001; Le Blanc et al, 2004; Rakotoarisoa et al, 2006).…”

“…These findings are consistent with earlier studies involving PI3K activation in the transduction pathways for the angiotensin II (AII)-induced Ca 2+ responses and contraction in VSM (Le Blanc et al, 2004; Rakotoarisoa et al, 2006). In vascular myocytes, PI3Kγ isoform was initially shown to mediate AII-induced activation of L-type voltage-dependent Ca 2+ currents, to increase [Ca 2+ ] i and elicit contraction (Quignard et al, 2001; Le Blanc et al, 2004; Rakotoarisoa et al, 2006). This is confirmed in the endothelium-denuded intact resistance arteries of the present study by the inhibitory effect of the PI3K blocker LY294002 on L-type Ca 2+ entry elicited by high K + depolarization.…”