title: N-Arachidonoyl glycine suppresses Na⁺/Ca²⁺ exchanger-mediated Ca²⁺ entry into endothelial cells and activates BK(Ca) channels independently of GPCRs.
abstract: OBJECTIVE
  N-Arachidonoyl glycine (NAGly) is a lipoamino acid with vasorelaxant properties. We aimed to explore the mechanisms of NAGly's action on unstimulated and agonist-stimulated endothelial cells.
  
  
  METHODS
  The effects of NAGly on endothelial electrical signalling were studied in combination with vascular reactivity.
  
  
  RESULTS
  In EA.hy926 cells, the sustained hyperpolarization to histamine was inhibited by the non-selective Na⁺/Ca²⁺ exchanger (NCX) inhibitor bepridil and by an inhibitor of reversed mode NCX, KB-R7943. In cells dialysed with Cs⁺-based Na⁺-containing solution, the outwardly rectifying current with typical characteristics of NCX was augmented following histamine exposure, further increased upon external Na⁺ withdrawal and inhibited by bepridil. NAGly (0.3-30 μM) suppressed NCX currents in a URB597- and guanosine 5'-O-(2-thiodiphosphate) (GDPβS)-insensitive manner, [Ca²⁺]i elevation evoked by Na⁺ removal and the hyperpolarization to histamine. In rat aorta, NAGly opposed the endothelial hyperpolarization and relaxation response to ACh. In unstimulated EA.hy926 cells, NAGly potentiated the whole-cell current attributable to large-conductance Ca²⁺-activated K⁺ (BK(Ca)) channels in a GDPβS-insensitive, paxilline-sensitive manner and produced a sustained hyperpolarization. In cell-free inside-out patches, NAGly stimulated single BK(Ca) channel activity.
  
  
  CONCLUSIONS
  Our data showed that NCX is a Ca²⁺ entry pathway in endothelial cells and that NAGly is a potent G-protein-independent modulator of endothelial electrical signalling and has a dual effect on endothelial electrical responses. In agonist pre-stimulated cells, NAGly opposes hyperpolarization and relaxation via inhibition of NCX-mediated Ca²⁺ entry, while in unstimulated cells, it promotes hyperpolarization via receptor-independent activation of BK(Ca) channels.
authors.affiliation: Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Graz, Austria. oleksandr.bondarenko@medunigraz.at
authors.forename: Alexander I
authors.initials: AI
authors.lastname: Bondarenko
authors.forename: Konstantin
authors.initials: K
authors.lastname: Drachuk
authors.forename: Olga
authors.initials: O
authors.lastname: Panasiuk
authors.forename: Vadim
authors.initials: V
authors.lastname: Sagach
authors.forename: Andras T
authors.initials: AT
authors.lastname: Deak
authors.forename: Roland
authors.initials: R
authors.lastname: Malli
authors.forename: Wolfgang F
authors.initials: WF
authors.lastname: Graier
mesh_terms: D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism; D001095:Arachidonic Acids / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects*; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002474:Cell-Free System / Q000187:drug effects / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006632:Histamine / Q000378:metabolism; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D066298:In Vitro Techniques; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000819:agonists* / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014661:Vasoconstriction / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D001095:Arachidonic Acids; D002121:Calcium Channel Blockers; D051036:Large-Conductance Calcium-Activated Potassium Channels; C465623:N-arachidonylglycine; D043562:Receptors, G-Protein-Coupled; D019831:Sodium-Calcium Exchanger; D014665:Vasodilator Agents; D006632:Histamine; D005998:Glycine