title: P2Y receptor-mediated transient relaxation of rat longitudinal ileum preparations involves phospholipase C activation, intracellular Ca(2+) release and SK channel activation.
abstract: OBJECTIVE
  Purinergic signaling plays a major role in the enteric nervous system, where it governs gut motility through a number of P2X and P2Y receptors. The aim of this study was to investigate the P2Y receptor-mediated motility in rat longitudinal ileum preparations.
  
  
  METHODS
  Ileum smooth muscle strips were prepared from rats, and fixed in an organ bath. Isometric contraction and relaxation responses of the muscle strips were measured with force transducers. Drugs were applied by adding of stock solutions to the organ bath to yield the individual final concentrations.
  
  
  RESULTS
  Application of the non-hydrolyzable P2 receptor agonists α,β-Me-ATP or 2-Me-S-ADP (10, 100 μmol/L) dose-dependently elicited a transient relaxation response followed by a sustained contraction. The relaxation response was largely blocked by SK channel blockers apamin (500 nmol/L) and UCL1684 (10 μmol/L), PLC inhibitor U73122 (100 μmol/L), IP3 receptor blocker 2-APB (100 μmol/L) or sarcoendoplasmic Ca(2+) ATPase inhibitor thapsigargin (1 μmol/L), but not affected by atropine, NO synthase blocker L-NAME or tetrodotoxin. Furthermore, α,β-Me-ATP-induced relaxation was suppressed by P2Y1 receptor antagonist MRS2179 (50 μmol/L) or P2Y13 receptor antagonist MRS2211 (100 μmol/L), and was abolished by co-application of the two antagonists, whereas 2-Me-S-ADP-induced relaxation was abolished by P2Y6 receptor antagonist MRS2578 (50 μmol/L). In addition, P2Y1 receptor antagonist MRS2500 (1 μmol/L) not only abolished α,β-Me-ATP-induced relaxation, but also suppressed 2-Me-S-ADP-induced relaxation.
  
  
  CONCLUSIONS
  P2Y receptor agonist-induced transient relaxation of rat ileum smooth muscle strips is mediated predominantly by P2Y1 receptor, but also by P2Y6 and P2Y13 receptors, and involves PLC, IP3, Ca(2+) release and SK channel activation, but is independent of acetylcholine and NO release.
authors.affiliation: Oscar Langendorff Institute of Physiology, University of Rostock, 18057 Rostock, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Mader
authors.affiliation: Oscar Langendorff Institute of Physiology, University of Rostock, 18057 Rostock, Germany.
authors.forename: Ludwig
authors.initials: L
authors.lastname: Krause
authors.affiliation: Oscar Langendorff Institute of Physiology, University of Rostock, 18057 Rostock, Germany.
authors.forename: Tursonjan
authors.initials: T
authors.lastname: Tokay
authors.affiliation: Department of Urology, University of Rostock, 18057 Rostock, Germany.
authors.forename: Oliver W
authors.initials: OW
authors.lastname: Hakenberg
authors.affiliation: Oscar Langendorff Institute of Physiology, University of Rostock, 18057 Rostock, Germany.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Köhling
authors.affiliation: Oscar Langendorff Institute of Physiology, University of Rostock, 18057 Rostock, Germany.
authors.forename: Timo
authors.initials: T
authors.lastname: Kirschstein
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004789:Enzyme Activation; D007082:Ileum / Q000502:physiology*; D066298:In Vitro Techniques; D042541:Intracellular Space / Q000378:metabolism; D007537:Isometric Contraction; D008297:Male; D009126:Muscle Relaxation; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D058912:Purinergic P2Y Receptor Agonists / Q000494:pharmacology; D017207:Rats, Sprague-Dawley; D058470:Receptors, Purinergic P2Y / Q000378:metabolism*; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D058912:Purinergic P2Y Receptor Agonists; D058470:Receptors, Purinergic P2Y; D051640:Small-Conductance Calcium-Activated Potassium Channels; D010738:Type C Phospholipases; D002118:Calcium