GPR55-dependent and -Independent Ion Signalling in Response to Lysophosphatidylinositol in Endothelial Cells

Br J Pharmacol. 2010 Sep;161(2):308-20. doi: 10.1111/j.1476-5381.2010.00744.x.

Abstract

Background and purpose: The glycerol-based lysophospholipid lysophosphatidylinositol (LPI) is an endogenous agonist of the G-protein-coupled receptor 55 (GPR55) exhibiting cannabinoid receptor-like properties in endothelial cells. To estimate the contribution of GPR55 to the physiological effects of LPI, the GPR55-dependent and -independent electrical responses in this cell type were investigated.

Experimental approach: Applying small interference RNA-mediated knock-down and transient overexpression, GPR55-dependent and -independent effects of LPI on cytosolic free Ca(2+) concentration, membrane potential and transmembrane ion currents were studied in EA.hy296 cells.

Key results: In a GPR55-dependent, GDPbetaS and U73122-sensitive manner, LPI induced rapid and transient intracellular Ca(2+) release that was associated with activation of charybdotoxin-sensitive, large conductance, Ca(2+)-activated, K(+) channels (BK(Ca)) and temporary membrane hyperpolarization. Following these initial electrical reactions, LPI elicited GPR55-independent long-lasting Na(+) loading and a non-selective inward current causing sustained membrane depolarization that depended on extracellular Ca(2+) and Na(+) and was partially inhibited by Ni(2+) and La(3+). This inward current was due to the activation of a voltage-independent non-selective cation current. The Ni(2+) and La(3+)-insensitive depolarization with LPI was prevented by inhibition of the Na/K-ATPase by ouabain.

Conclusions and implications: LPI elicited a biphasic response in endothelial cells of which the immediate Ca(2+) signalling depends on GPR55 while the subsequent depolarization is due to Na(+) loading via non-selective cation channels and an inhibition of the Na/K-ATPase. Thus, LPI is a potent signalling molecule that affects endothelial functions by modulating several cellular electrical responses that are only partially linked to GPR55.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calcium / metabolism
  • Calcium Signaling / drug effects
  • Calcium Signaling / physiology*
  • Cell Line
  • Cytosol / drug effects
  • Cytosol / metabolism
  • Cytosol / physiology
  • Endothelial Cells / drug effects
  • Endothelial Cells / metabolism
  • Endothelial Cells / physiology*
  • Humans
  • Ion Transport / drug effects
  • Ion Transport / physiology
  • Lysophospholipids / pharmacology
  • Lysophospholipids / physiology*
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Potassium Channels, Calcium-Activated / metabolism
  • RNA, Small Interfering
  • Receptors, G-Protein-Coupled / agonists
  • Receptors, G-Protein-Coupled / antagonists & inhibitors
  • Receptors, G-Protein-Coupled / genetics
  • Receptors, G-Protein-Coupled / physiology*
  • Sodium / metabolism
  • Sodium-Potassium-Exchanging ATPase / antagonists & inhibitors
  • Transfection

Substances

  • GPR55 protein, human
  • Lysophospholipids
  • Potassium Channels, Calcium-Activated
  • RNA, Small Interfering
  • Receptors, G-Protein-Coupled
  • lysophosphatidylinositol
  • Sodium
  • Sodium-Potassium-Exchanging ATPase
  • Calcium