title: Perivascular cells with pericyte characteristics are involved in ATP- and PGE(2)-induced relaxation of porcine retinal arterioles in vitro.
abstract: OBJECTIVE
  Relaxation of porcine retinal arterioles in vitro has been shown to be preceded by calcium activity in a population of perivascular cells that cannot be classified as neurons, glial cells, or vascular smooth muscle cells. The purpose of the present investigation was to study calcium activity in these perivascular cells during ATP- and PGE2-induced vasorelaxation, and to identify pericyte markers and other cellular constituents characterizing these cells.
  
  
  METHODS
  Porcine arterioles were loaded with a calcium-sensitive fluorophore and mounted in a myograph. Simultaneous measurements of calcium activity and vascular tone during stimulation with ATP and PGE2 were performed before and after addition of specific antagonists to these compounds and to nitric oxide. Additionally, immunohistochemistry was performed on whole mounts of porcine retina using antibodies to known markers of vascular pericytes and cellular components of the vascular wall.
  
  
  RESULTS
  Relaxation of retinal arterioles with both ATP and PGE2 was preceded by a significant increase in the number of perivascular cells displaying calcium activity. The effect of ATP was inhibited by the adenosine receptor antagonist 8-PSPT, whereas the effect of PGE2 was inhibited by the EP1 receptor antagonist SC19220 and the NO-synthesis inhibitor L-NAME. The perivascular cells had morphological features in common with pericytes and displayed immunoreactivity to the pericyte markers NG2 and CD-13, but not to markers of glial cells, neurons, or vascular smooth muscle cells.
  
  
  CONCLUSIONS
  The perivascular cell type located external to the smooth muscle cells in porcine retinal arterioles shows calcium activity during relaxation with ATP and PGE2 and has morphological properties in common with pericytes. Future studies should focus on the role of this cell type for regulating retinal blood flow and for retinal vascular disease.
authors.affiliation: Department of Ophthalmology, Aarhus University Hospital, Aarhus C, Denmark. mikkelmisfeldt@gmail.com
authors.forename: Mikkel Wölck
authors.initials: MW
authors.lastname: Misfeldt
authors.forename: Simon Metz Mariendal
authors.initials: SM
authors.lastname: Pedersen
authors.forename: Toke
authors.initials: T
authors.lastname: Bek
mesh_terms: D000255:Adenosine Triphosphate / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D001160:Arterioles / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D015232:Dinoprostone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005452:Fluoresceins / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D005456:Fluorescent Dyes; D018613:Microscopy, Confocal; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D009213:Myography; D020286:Pericytes / Q000378:metabolism*; D011448:Prostaglandin Antagonists / Q000494:pharmacology; D012161:Retinal Artery / Q000502:physiology*; D034421:Sus scrofa; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D014664:Vasodilation / Q000502:physiology*
chemical_list: D000814:Aniline Compounds; D005452:Fluoresceins; D005456:Fluorescent Dyes; C503942:Oregon green 488 BAPTA-1; D011448:Prostaglandin Antagonists; C031433:8-(4-sulfophenyl)theophylline; D000255:Adenosine Triphosphate; D013806:Theophylline; D015232:Dinoprostone; D002118:Calcium
keywords: ATP; calcium; nitric oxide; pericyte; prostaglandin E2; retinal arterioles