title: P2Y₂ receptor activation decreases blood pressure via intermediate conductance potassium channels and connexin 37.
abstract: OBJECTIVE
  Nucleotides are important paracrine regulators of vascular tone. We previously demonstrated that activation of P2Y₂ receptors causes an acute, NO-independent decrease in blood pressure, indicating this signalling pathway requires an endothelial-derived hyperpolarization (EDH) response. To define the mechanisms by which activation of P2Y₂ receptors initiates EDH and vasodilation, we studied intermediate-conductance (KCa3.1, expressed in endothelial cells) and big-conductance potassium channels (KCa1.1, expressed in smooth muscle cells) as well as components of the myoendothelial gap junction, connexins 37 and 40 (Cx37, Cx40), all hypothesized to be part of the EDH response.
  
  
  METHODS
  We compared the effects of a P2Y₂/₄ receptor agonist in wild-type (WT) mice and in mice lacking KCa3.1, KCa1.1, Cx37 or Cx40 under anaesthesia, while monitoring intra-arterial blood pressure and heart rate.
  
  
  RESULTS
  Acute activation of P2Y₂/₄ receptors (0.01-3 mg kg(-1) body weight i.v.) caused a biphasic blood pressure response characterized by a dose-dependent and rapid decrease in blood pressure in WT (maximal response % of baseline at 3 mg kg(-1) : -38 ± 1%) followed by a consecutive increase in blood pressure (+44 ± 11%). The maximal responses in KCa3.1(-/-) and Cx37(-/-) were impaired (-13 ± 5, +17 ± 7 and -27 ± 1, +13 ± 3% respectively), whereas the maximal blood pressure decrease in response to acetylcholine at 3 μg kg(-1) was not significantly different (WT: -53 ± 3%; KCa3.1(-/-) : -52 ± 3; Cx37(-/-) : -53 ± 3%). KCa1.1(-/-) and Cx40(-/-) showed an identical biphasic response to P2Y2/4 receptor activation compared to WT.
  
  
  CONCLUSIONS
  The data suggest that the P2Y2/4 receptor activation elicits blood pressure responses via distinct mechanisms involving KCa3.1 and Cx37.
authors.affiliation: Department of Basic Sciences, Bastyr University California, San Diego, CA, USA; VA San Diego Healthcare System, San Diego, CA, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Dominguez Rieg
authors.forename: J M
authors.initials: JM
authors.lastname: Burt
authors.forename: P
authors.initials: P
authors.lastname: Ruth
authors.forename: T
authors.initials: T
authors.lastname: Rieg
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D017630:Connexins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D006339:Heart Rate / Q000187:drug effects; D007288:Inosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000235:genetics / Q000378:metabolism; D008297:Male; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000235:genetics / Q000378:metabolism; D058912:Purinergic P2Y Receptor Agonists; D058473:Receptors, Purinergic P2Y2 / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014544:Uridine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects; D000097006:Gap Junction alpha-4 Protein
chemical_list: D017630:Connexins; D007288:Inosine; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D052250:Nitric Oxide Synthase Type III; D058912:Purinergic P2Y Receptor Agonists; D058473:Receptors, Purinergic P2Y2; D014544:Uridine Triphosphate; D000097006:Gap Junction alpha-4 Protein; C561698:INS45973; C465449:Kcnma1 protein, mouse; C496925:Kcnn4 protein, mouse; C496315:Nos3 protein, mouse
keywords: K+ channels; P2 receptors; gap junction; hyperpolarization; myogenic tone; signalling