title: Extracellular nucleotides affect pericyte-mediated regulation of rat in situ vasa recta diameter.
abstract: OBJECTIVE
  We hypothesized that extracellular nucleotides, established as being released from renal tubular epithelial cells, act at pericytes to regulate vasa recta capillary diameter.
  
  
  METHODS
  A rat live kidney slice model and video imaging techniques were used to investigate the effects of extracellular nucleotides on in situ (subsurface) vasa recta diameter at pericyte and non-pericyte sites. In addition, RT-qPCR was used to quantify P2 receptor mRNA expression in isolated vasa recta.
  
  
  RESULTS
  Extracellular ATP, UTP, benzylbenzyl ATP (BzATP) or 2-methylthioATP (2meSATP) evoked a significantly greater vasoconstriction of subsurface vasa recta at pericytes than at non-pericyte sites. The rank order of agonist potency was BzATP = 2meSATP > ATP = UTP. The vasoconstriction evoked at pericyte sites by ATP was significantly attenuated by the P2 receptor antagonists suramin, pyridoxal phosphate-6-azo(benzene-2,4-disulfonic acid) (PPADS) or Reactive Blue-2 (RB-2). UTP-evoked vasoconstriction at pericytes was attenuated by suramin or RB-2 but not PPADS. Interestingly, suramin or PPADS, when applied in the absence of a P2 receptor agonist, evoked a weak but significant vasoconstriction of vasa recta at pericyte sites, suggesting tonic vasodilation by nucleotides. Significant levels of P2X(1, 3 and 7) and P2Y(4 and 6) receptor mRNA were detected in vasa recta.
  
  
  CONCLUSIONS
  Extracellular nucleotides act at pericytes to cause vasoconstriction of in situ vasa recta. Pharmacological characterization, supported by RT-qPCR data, suggests that P2X(1 and 7) and P2Y(4) receptors mediate nucleotide-evoked vasoconstriction of vasa recta by pericytes. We propose that nucleotides released from renal tubular epithelial cells, in close proximity to vasa recta capillaries, are key in regulating renal medullary blood flow.
authors.affiliation: Urinary System Physiology Unit, Department of Veterinary Basic Sciences, Royal Veterinary College, London, UK.
authors.forename: C
authors.initials: C
authors.lastname: Crawford
authors.forename: T M
authors.initials: TM
authors.lastname: Kennedy-Lydon
authors.forename: H
authors.initials: H
authors.lastname: Callaghan
authors.forename: C
authors.initials: C
authors.lastname: Sprott
authors.forename: R L
authors.initials: RL
authors.lastname: Simmons
authors.forename: L
authors.initials: L
authors.lastname: Sawbridge
authors.forename: H M
authors.initials: HM
authors.lastname: Syme
authors.forename: R J
authors.initials: RJ
authors.lastname: Unwin
authors.forename: S S P
authors.initials: SS
authors.lastname: Wildman
authors.forename: C M
authors.initials: CM
authors.lastname: Peppiatt-Wildman
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D004730:Endothelium, Vascular / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008297:Male; D009711:Nucleotides / Q000494:pharmacology*; D020286:Pericytes / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D058913:Purinergic Agonists / Q000494:pharmacology; D058914:Purinergic Antagonists / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011983:Receptors, Purinergic / Q000235:genetics / Q000378:metabolism; D014544:Uridine Triphosphate / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects
chemical_list: D009711:Nucleotides; D058913:Purinergic Agonists; D058914:Purinergic Antagonists; D011983:Receptors, Purinergic; C033901:3'-O-(4-benzoyl)benzoyladenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D014544:Uridine Triphosphate