Phospholipase C-δ1modulates sustained contraction of rat mesenteric small arteries in response to noradrenaline, but not endothelin-1

Abstract

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 PIP2hydrolysis and contraction. Rat mesenteric small arteries were studied. Contractility was measured by pressure myography, phospholipids or inositol phosphates were measured by radiolabeling with33Pi or myo-[3H]inositol, and caveolae/rafts were prepared by discontinuous sucrose density centrifugation. PLC-δ1was localized by immunoblot analysis and neutralized by delivery of PLC-δ1antibody. 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-δ1was present in caveolae/rafts, and NA, but not ET-1, stimulated a rapid twofold increase in PLC-δ1levels in these domains. PLC-δ1is calcium dependent, and removal of extracellular calcium prevented its association with caveolae/rafts in response to NA, concomitantly reducing NA-induced [33P]PIP2hydrolysis and [3H]inositol phosphate formation but with no effect on ET-1-induced [33P]PIP2hydrolysis. Neutralization of PLC-δ1by PLC-δ1antibody 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-δ1antibody. These results indicate the novel and selective role of caveolae/raft localized PLC-δ1in NA-induced PIP2hydrolysis and sustained contraction in intact vascular tissue.