PLA2 and TRPV4 channels regulate endothelial calcium in cerebral arteries

Am J Physiol Heart Circ Physiol. 2007 Mar;292(3):H1390-7. doi: 10.1152/ajpheart.01006.2006. Epub 2006 Oct 27.

Abstract

We previously demonstrated that endothelium-derived hyperpolarizing factor (EDHF)-mediated dilations in cerebral arteries are significantly reduced by inhibitors of PLA(2). In this study we examined possible mechanisms by which PLA(2) regulates endothelium-dependent dilation, specifically whether PLA(2) is involved in endothelial Ca(2+) regulation through stimulation of TRPV4 channels. Studies were carried out with middle cerebral arteries (MCA) or freshly isolated MCA endothelial cells (EC) of male Long-Evans rats. Nitro-l-arginine methyl ester (l-NAME) and indomethacin were present throughout. In pressurized MCA, luminally delivered UTP produced increased EC intracellular Ca(2+) concentration ([Ca(2+)](i)) and MCA dilation. Incubation with PACOCF(3), a PLA(2) inhibitor, significantly reduced both EC [Ca(2+)](i) and dilation responses to UTP. EC [Ca(2+)](i) was also partially reduced by a transient receptor potential vanilloid (TRPV) channel blocker, ruthenium red. Manganese quenching experiments demonstrated Ca(2+) influx across the luminal and abluminal face of the endothelium in response to UTP. Interestingly, PLA(2)-sensitive Ca(2+) influx occurred primarily across the abluminal face. Luminal application of arachidonic acid, the primary product of PLA(2) and a demonstrated activator of certain TRPV channels, increased both EC [Ca(2+)](i) and MCA diameter. TRPV4 mRNA and protein was demonstrated in the endothelium by RT-PCR and immunofluorescence, respectively. Finally, application of 4alpha-phorbol 12,13-didecanoate (4alphaPDD), a TRPV4 channel activator, produced an increase in EC [Ca(2+)](i) that was significantly reduced in the presence of ruthenium red. We conclude that PLA(2) is involved in EC Ca(2+) regulation through its regulation of TRPV4 channels. Furthermore, the PLA(2)-sensitive component of Ca(2+) influx may be polarized to the abluminal face of the endothelium.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Arachidonic Acid / pharmacology
  • Calcium / physiology*
  • DNA Primers
  • Endothelium, Vascular / drug effects
  • Endothelium, Vascular / physiology*
  • In Vitro Techniques
  • Manganese / metabolism
  • Middle Cerebral Artery / drug effects
  • Middle Cerebral Artery / physiology*
  • Nitric Oxide Synthase Type III / genetics
  • Phospholipases A / metabolism*
  • Phospholipases A2
  • Polymerase Chain Reaction
  • Rats
  • Ruthenium Red / pharmacology
  • TRPV Cation Channels / physiology*

Substances

  • DNA Primers
  • TRPV Cation Channels
  • Trpv4 protein, rat
  • Ruthenium Red
  • Arachidonic Acid
  • Manganese
  • Nitric Oxide Synthase Type III
  • Phospholipases A
  • Phospholipases A2
  • Calcium