Phospholipase C-δ₁ modulates sustained contraction of rat mesenteric small arteries in response to noradrenaline, but not endothelin-1

Vasoconstrictors activate phospholipase C (PLC), which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP₂), leading to calcium mobilization, protein kinase C activation, and contraction. Our aim was to investigate whether PLC-δ₁, a PLC isoform implicated in α₁-adrenoreceptor signaling and the pathogenesis of hypertension, is involved in noradrenaline (NA) or endothelin (ET-1)-induced PIP2 hydrolysis and contraction. Rat mesenteric small arteries were studied. Contractility was measured by pressure myography, phospholipids or inositol phosphates were measured by radiolabeling with ³³Pi or myo-[ ³H]inositol, and caveolae/rafts were prepared by discontinuous sucrose density centrifugation. PLC-δ₁ was localized by immunoblot analysis and neutralized by delivery of PLC-δ₁ antibody. The PLC inhibitor U73122, but not the negative control U-73342, markedly inhibited NA and ET-1 contraction but had no effect on potassium or phorbol ester contraction, implicating PLC activity in receptor-mediated smooth muscle contraction. PLC-δ₁ was present in caveolae/rafts, and NA, but not ET-1, stimulated a rapid twofold increase in PLC-δ₁ levels in these domains. PLC-δ₁ is calcium dependent, and removal of extracellular calcium prevented its association with caveolae/rafts in response to NA, concomitantly reducing NA-induced [³³P]PIP ₂ hydrolysis and [³H]inositol phosphate formation but with no effect on ET-1-induced [³³P]PIP₂ hydrolysis. Neutralization of PLC-δ₁ by PLC-δ₁ antibody prevented its caveolae/raft association and attenuated the sustained contractile response to NA compared with control antibodies. In contrast, ET-1-induced contraction was not affected by PLC-δ₁ antibody. These results indicate the novel and selective role of caveolae/raft localized PLC-δ₁ in NA-induced PIP₂ hydrolysis and sustained contraction in intact vascular tissue.