title: Genetic ablation of calcium-independent phospholipase A(2)beta causes hypercontractility and markedly attenuates endothelium-dependent relaxation to acetylcholine.
abstract: Activation of phospholipases leads to the release of arachidonic acid and lysophospholipids that play prominent roles in regulating vasomotor tone. To identify the role of calcium-independent phospholipase A(2)beta (iPLA(2)beta) in vasomotor function, we measured vascular responses to phenylephrine (PE) and ACh in mesenteric arterioles from wild-type (WT; iPLA(2)beta(+/+)) mice and those lacking the beta-isoform (iPLA(2)beta(-/-)) both ex vivo and in vivo. Vessels isolated from iPLA(2)beta(-/-) mice demonstrated increased constriction to PE, despite lower basal smooth muscle calcium levels, and decreased vasodilation to ACh compared with iPLA(2)beta(+/+) mice. PE constriction resulted in initial intracellular calcium release with subsequent steady-state constriction that depended on extracellular calcium influx. Endothelial denudation had no effect on vessel tone or PE-induced constriction although the dilation to ACh was significantly reduced in iPLA(2)beta(+/+) vessels. In contrast, vessels from iPLA(2)beta(-/-) constricted by 54% after denudation, indicating smooth muscle hypercontractility. In vivo, blood pressure, resting vessel diameter, and constriction of mesenteric vessels to PE were not different in iPLA(2)beta(-/-) vessels compared with WT mouse vessels. However, relaxation after ACh administration in situ was attenuated, indicating an endothelial inability to induce dilation in response to ACh. In cultured endothelial cells, inhibition of iPLA(2)beta with (S)-(E)-6-(bromomethylene)tetrahydro-3-(1-naphthalenyl)-2H-pyran-2-one (BEL) decreased endothelial nitric oxide synthase phosphorylation and reduced endothelial agonist-induced intracellular calcium release as well as extracellular calcium influx. We conclude that iPLA(2)beta is an important mediator of vascular relaxation and intracellular calcium homeostasis in both smooth muscle and endothelial cells and that ablation of iPLA(2)beta causes agonist-induced smooth muscle hypercontractility and reduced agonist-induced endothelial dilation.
authors.affiliation: Washington Univ. School of Medicine, Dept. of Neurosurgery, 660 South Euclid Ave., Campus Box 8057, St. Louis, MO 63110, USA. Dietrich_H@wustl.edu
authors.forename: Hans H
authors.initials: HH
authors.lastname: Dietrich
authors.forename: Dana R
authors.initials: DR
authors.lastname: Abendschein
authors.forename: Sung Ho
authors.initials: SH
authors.lastname: Moon
authors.forename: Neema
authors.initials: N
authors.lastname: Nayeb-Hashemi
authors.forename: David J
authors.initials: DJ
authors.lastname: Mancuso
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Jenkins
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Kaltenbronn
authors.forename: Kendall J
authors.initials: KJ
authors.lastname: Blumer
authors.forename: John
authors.initials: J
authors.lastname: Turk
authors.forename: Richard W
authors.initials: RW
authors.lastname: Gross
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D054522:Group VI Phospholipases A2 / Q000235:genetics / Q000502:physiology; D006706:Homeostasis / Q000502:physiology; D008297:Male; D008638:Mesenteric Arteries / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D023421:Models, Animal; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D010656:Phenylephrine / Q000494:pharmacology; D054512:Phospholipases A2, Calcium-Independent / Q000235:genetics* / Q000502:physiology*; D010766:Phosphorylation; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D010656:Phenylephrine; D052250:Nitric Oxide Synthase Type III; D054522:Group VI Phospholipases A2; D054512:Phospholipases A2, Calcium-Independent; C516476:Pla2g6 protein, mouse; D000109:Acetylcholine; D002118:Calcium
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