Calcium-Independent Phospholipase A₂-Derived Arachidonic Acid Is Essential for Endothelium-Dependent Relaxation by Acetylcholine

Abstract

The role of calcium-independent phospholipase A 2 (iPLA 2 )-produced arachidonic acid (AA) in acetylcholine (ACh)-mediated, endothelium-dependent vascular relaxation was investigated. ACh-induced relaxation of phenylephrine-constricted isolated rat mesenteric resistance arteries was attenuated following pretreatment with (E)-6-(bromomethylene)tetrahydro-3-(1-naphthalenyl)-2H-pyran-2-one (BEL; 1 M; p Ͻ 0.01), a highly selective suicide substrate inhibitor of iPLA 2 . Following BEL, the ACh relaxation could be completely restored following pretreatment with picomolar quantities of the cell-permeant methyl ester analog of AA (arachidonic acid methyl ester, AAMe). Higher amounts of AA-Me (1 M) had a direct endothelium-dependent relaxing action, which was inhibited by the nitric-oxide synthase inhibitor (N -nitro-L-arginine; 100 M), independent of ACh, and unaffected by BEL. Neither the ACh relaxation restoring action nor the direct relaxing action of AA-Me was affected by preincubation with inhibitors of the lipoxygenase (esculetin, 10 M) or cytochrome P450 monooxygenase (17-octadecynoic acid; 10 M) pathways; and both actions of AA-Me were enhanced following preincubation with the cyclooxygenase inhibitor indomethacin (10 M; p Ͻ 0.05). The results of the present study indicate that iPLA 2 -produced AA plays an essential role in ACh-mediated endothelium-dependent relaxation in rat mesenteric resistance arteries.Vascular endothelium modulates blood pressure and flow by producing and releasing factors, which regulate the tone of the underlying smooth muscle. The pivotal role of endothelium-derived relaxing factor, now known to be nitric oxide (NO) generated from the metabolism of L-arginine, is well established (Palmer et al., 1987). In addition, other factors including AA and its metabolites may also contribute significantly to endothelium-mediated relaxation (for reviews, see Quilley et al

Bromoenol Lactone Inhibits Voltage-Gated Ca2+and Transient Receptor Potential Canonical Channels

“…Compelling evidence indicates that, in vascular smooth muscle cells, store depletion induces iPLA 2 activity. This leads to the stimulation of store-operated Ca 2ϩ -permeable channels (Wolf and Gross, 1996;Wolf et al, 1997;Seegers et al, 2002;Smani et al, 2004;Bolotina and Csutora, 2005). Because BEL, a selective inhibitor of the cytosolic ␤-isoform of iPLA 2 (Jenkins et al, 2003), totally inhibited store-operated channel activation, it has emerged as a vital tool for revealing the role of SOC channels during contractile responses in various vascular beds.…”

“…It has been proposed that phenylephrine-induced Ca 2ϩ influx is mediated solely by iPLA 2 -dependent SOC channels, because BEL pretreatment totally eliminated phenylephrine-induced contractions in mesenteric, cerebral, and carotid arteries (Park et al, 2008). Conversely, another report indicated that BEL did not affect phenylephrine contractions but inhibited acetylcholine-induced endothelium-dependent relaxation (Seegers et al, 2002). To clarify these discrepancies and establish if BEL inhibits other proteins involved in Ca 2ϩ homeostasis, we …”

“…The findings that Ca 2ϩ -independent phospholipase A 2 (iPLA 2 ) is activated upon store depletion and plays a key role during SOC channel activation (Fig. 1A) (Wolf and Gross, 1996;Wolf et al, 1997;Seegers et al, 2002) prompted the use of a specific inhibitor of iPLA 2 , E-6-(bromoethylene)tetrahydro-3-(1-naphthyl)-2H-pyran-2-one (bromoenol lactone, BEL; Fig. 1A), for defining SOC channel functions in various physiological and pathophysiological systems.…”

Phospholipase A2 Activity-Dependent Stimulation of Ca 2+ Entry by Human Parvovirus B19 Capsid Protein VP1

“…The pleiotropic actions of phospholipase A2 (73,84) include the stimulation of smooth muscle and endothelial cells (22,72). Altered regulation of cytosolic Ca 2ϩ activity is expected to affect a wide variety of cellular functions.…”

Inhibition of Ca2+-Independent Phospholipase A2 Decreases Prostate Cancer Cell Growth by p53-Dependent and Independent Mechanisms

“…However, it recently has drawn attention as a cell growth regulator because of its possible role in insulin secretion (Ramanadham et al, 1999), eicosanoid metabolism (Akiba et al, 1998), phospholipid remodeling , apoptosis (Atsumi et al, 2000;Cummings et al, 2004), vascular relaxation (Seegers et al, 2002), and adipogenesis (Su et al, 2004). Recent studies also suggest that iPLA 2 mediates cell proliferation in HEK293 (Saavedra et al, 2006), human insulinoma, colon cancer (Bao et al, 2006;Zhang et al, 2006), and ovarian cancer cells (Song et al, 2007).…”