title: ATP-evoked sustained vasoconstrictions mediated by heteromeric P2X1/4 receptors in cerebral arteries.
abstract: OBJECTIVE
  Current knowledge states that vasoconstrictor responses to ATP are mediated by rapidly desensitizing ligand-gated P2X1 receptors in vascular smooth muscle cells (VSMCs). However, ATP is implicated in contributing to pathological conditions involving sustained vasoconstrictor response such as cerebral vasospasm. The purpose of this study is to test the hypothesis that the stimulation of VSMC P2XR receptors (P2XRs) contributes to ATP-evoked sustained vasoconstrictions in rat middle cerebral arteries (RMCAs).
  
  
  METHODS
  Reverse transcription- polymerase chain reaction, Western blot, and immunocytochemistry were used to analyze expression of mRNA and proteins in RMCAs VSMCs. Ionic currents and calcium responses were investigated using patch-clamp and confocal imaging techniques, respectively. Functional responses were confirmed using wire myography.
  
  
  RESULTS
  Expression of mRNA and protein for P2X1R and P2X4R subunits was identified in RMCA VSMCs. Confocal imaging in fluo-3-loaded VSMCs showed that ATP and a selective P2XR agonist, αβmeATP, evoked similar dose-dependent increases in [Ca(2+)]i. Patch-clamp experiments identified 2 components of P2XR-mediated currents: consisting of a fast desensitizing phase mediated by homomeric P2X1Rs and a slowly desensitizing phase involving heteromeric P2X1/4Rs. Isometric tension measurements showed that ≈80%:20% of initial ATP-evoked vasoconstriction in RMCA is mediated by homomeric P2X1Rs and heteromeric P2X1/4Rs, respectively. The sustained slowly desensitizing and rapidly recovering from desensitization responses are mediated by heteromeric P2X1/4Rs.
  
  
  CONCLUSIONS
  This study reveals for the first time that apart from rapidly desensitizing homomeric P2X1Rs, heteromeric P2X1/4Rs contribute to the sustained component of the purinergic-mediated vasoconstriction in RMCA. Our study, therefore, identifies possible novel targets for therapeutical intervention in cerebral circulation.
authors: From the Division of Biomedical Sciences, St George's, University of London, London, United Kingdom (M.I.H., O.V.P., A.P.A., C.M.N.); and Laboratory of Molecular Pharmacology and Biophysics of Cell Signalling, Bogomoletz Institute of Physiology, Kyiv, Ukraine (O.V.P.). m.harhun@gmail.com.
authors: Maksym I
authors: MI
authors: Harhun
authors: From the Division of Biomedical Sciences, St George's, University of London, London, United Kingdom (M.I.H., O.V.P., A.P.A., C.M.N.); and Laboratory of Molecular Pharmacology and Biophysics of Cell Signalling, Bogomoletz Institute of Physiology, Kyiv, Ukraine (O.V.P.).
authors: Oleksandr V
authors: OV
authors: Povstyan
authors: From the Division of Biomedical Sciences, St George's, University of London, London, United Kingdom (M.I.H., O.V.P., A.P.A., C.M.N.); and Laboratory of Molecular Pharmacology and Biophysics of Cell Signalling, Bogomoletz Institute of Physiology, Kyiv, Ukraine (O.V.P.).
authors: Anthony P
authors: AP
authors: Albert
authors: From the Division of Biomedical Sciences, St George's, University of London, London, United Kingdom (M.I.H., O.V.P., A.P.A., C.M.N.); and Laboratory of Molecular Pharmacology and Biophysics of Cell Signalling, Bogomoletz Institute of Physiology, Kyiv, Ukraine (O.V.P.).
authors: Claire M
authors: CM
authors: Nichols
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002536:Cerebral Arteries / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051381:Rats; D011921:Rats, Inbred WKY; D058474:Receptors, Purinergic P2X1 / Q000378:metabolism*; D058848:Receptors, Purinergic P2X4 / Q000378:metabolism*; D014661:Vasoconstriction / Q000187:drug effects* / Q000502:physiology
chemical_list: D058474:Receptors, Purinergic P2X1; D058848:Receptors, Purinergic P2X4; D000255:Adenosine Triphosphate; D002118:Calcium
keywords: adenosine triphosphate; cerebrovascular circulation