title: Sphingosine 1-phosphate enhances the excitability of rat sensory neurons through activation of sphingosine 1-phosphate receptors 1 and/or 3.
abstract: BACKGROUND
  Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that acts through a family of five G-protein-coupled receptors (S1PR1-5) and plays a key role in regulating the inflammatory response. Our previous studies demonstrated that rat sensory neurons express the mRNAs for all five S1PRs and that S1P increases neuronal excitability primarily, but not exclusively, through S1PR1. This raises the question as to which other S1PRs mediate the enhanced excitability.
  
  
  METHODS
  Isolated sensory neurons were treated with either short-interfering RNAs (siRNAs) or a variety of pharmacological agents targeted to S1PR1/R2/R3 to determine the role(s) of these receptors in regulating neuronal excitability. The excitability of isolated sensory neurons was assessed by using whole-cell patch-clamp recording to measure the capacity of these cells to fire action potentials (APs).
  
  
  RESULTS
  After siRNA treatment, exposure to S1P failed to augment the excitability. Pooled siRNA targeted to S1PR1 and R3 also blocked the enhanced excitability produced by S1P. Consistent with the siRNA results, pretreatment with W146 and CAY10444, selective antagonists for S1PR1 and S1PR3, respectively, prevented the S1P-induced increase in neuronal excitability. Similarly, S1P failed to augment excitability after pretreatment with either VPC 23019, which is a S1PR1 and R3 antagonist, or VPC 44116, the phosphonate analog of VPC 23019. Acute exposure (10 to 15 min) to either of the well-established functional antagonists, FTY720 or CYM-5442, produced a significant increase in the excitability. Moreover, after a 1-h pretreatment with FTY720 (an agonist for S1PR1/R3/R4/R5), neither SEW2871 (S1PR1 selective agonist) nor S1P augmented the excitability. However, after pretreatment with CYM-5442 (selective for S1PR1), SEW2871 was ineffective, but S1P increased the excitability of some, but not all, sensory neurons.
  
  
  CONCLUSIONS
  These results demonstrate that the enhanced excitability produced by S1P is mediated by activation of S1PR1 and/or S1PR3.
authors.affiliation: Medical Neuroscience Program, School of Medicine, Indiana University, Indianapolis, IN, 46202, USA. cdlichao@gmail.com.
authors.forename: Chao
authors.initials: C
authors.lastname: Li
authors.affiliation: Department of Pharmacology and Toxicology, School of Medicine, Indiana University, 635 Barnhill Drive, Indianapolis, IN, 46202, USA. junnli@iupui.edu.|Department of Pharmacology, Harbin Medical University, Harbin, Peoples' Republic of China. junnli@iupui.edu.
authors.forename: Jun-nan
authors.initials: JN
authors.lastname: Li
authors.affiliation: Department of Pharmacology and Toxicology, School of Medicine, Indiana University, 635 Barnhill Drive, Indianapolis, IN, 46202, USA. kaysj@iupui.edu.
authors.forename: Joanne
authors.initials: J
authors.lastname: Kays
authors.affiliation: Department of Chemistry, The Scripps Research Institute, La Jolla, CA, 92037, USA. miguelg@scripps.edu.
authors.forename: Miguel
authors.initials: M
authors.lastname: Guerrero
authors.affiliation: Department of Pharmacology and Toxicology, School of Medicine, Indiana University, 635 Barnhill Drive, Indianapolis, IN, 46202, USA. gnicol@iupui.edu.
authors.forename: Grant D
authors.initials: GD
authors.lastname: Nicol
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000813:Anilides / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D015232:Dinoprostone / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000068876:Fingolimod Hydrochloride / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000166:cytology; D005786:Gene Expression Regulation / Q000187:drug effects; D007166:Immunosuppressive Agents / Q000494:pharmacology; D008246:Lysophospholipids / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D063065:Organophosphonates / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D049349:Receptors, Lysosphingolipid / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011984:Sensory Receptor Cells / Q000187:drug effects*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000081025:Sphingosine-1-Phosphate Receptors; D053778:Thiazolidines / Q000494:pharmacology
chemical_list: C513113:3-amino-4-(3-hexylphenylamino)-4-oxobutylphosphonic acid; D000813:Anilides; C000609617:CAY10444; D004791:Enzyme Inhibitors; D007166:Immunosuppressive Agents; D008246:Lysophospholipids; D063065:Organophosphonates; D034741:RNA, Small Interfering; D049349:Receptors, Lysosphingolipid; C556330:S1pr1 protein, mouse; C501285:S1pr3 protein, mouse; D000081025:Sphingosine-1-Phosphate Receptors; D053778:Thiazolidines; C060506:sphingosine 1-phosphate; D000068876:Fingolimod Hydrochloride; D015232:Dinoprostone; D013110:Sphingosine