title: Endothelin-1-induced proliferation is reduced and Ca²⁺ signaling is enhanced in endothelin B-deficient optic nerve head astrocytes.
abstract: OBJECTIVE
  To characterize the influence of endothelin-1 (ET-1) on optic nerve head astrocyte (ONHA) proliferation and Ca²⁺ signaling in ONHAs lacking functional endothelin B (ETB) receptors.
  
  
  METHODS
  ONHAs were isolated from adult wild type (WT) and transgenic spotting lethal (TSL) rats, lacking functional ETB receptors. ONHA specificity was confirmed by positive glial fibrillary acidic protein (GFAP), negative A2B5 (a marker for type II astrocytes located outside the optic nerve head) and myelin basic protein (MBP) labeling. The mitogenic effects of 10⁻⁷ or 10⁻⁹ M ET-1, or vehicle were investigated for 48 or 72 hours in WT and TSL ONHAs. Intracellular calcium levels ([Ca²⁺](i)) were assessed in ONHAs loaded with fura-2 calcium indicator dye.
  
  
  RESULTS
  ET-1-induced proliferation of TSL ONHAs was blunted at 48 hours (by 37% at 10⁻⁷ M and by 33% at 10⁻⁹ M) and 72 hours (by 117% at 10⁻⁷ M and by 100% at 10⁻⁹ M) compared with WT cells. ET-1-induced ONHA fura-2 ratio increases were significantly greater in TSL ONHAs (by 20% at 10⁻⁷ M and by 48% at 10⁻⁹ M) compared with WT ONHAs. ET-1-induced fura-2 ratio increases were blocked after pretreatment with BQ-610 (ETA antagonist) in WT and TSL ONHAs, but not by BQ-788 (ETB antagonist) in WT ONHAs.
  
  
  CONCLUSIONS
  ET-1-induced ONHA proliferation is reduced in cells lacking functional ETB receptors, ET-1-induced [Ca²⁺](i) increases are enhanced in the absence of functional ETB receptors, and ETA, but not ETB, is required for ET-1-induced [Ca²⁺](i) elevation.
authors.affiliation: Retina and Optic Nerve Research Laboratory, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Jeremy A
authors.initials: JA
authors.lastname: Murphy
authors.forename: Michele L
authors.initials: ML
authors.lastname: Archibald
authors.forename: William H
authors.initials: WH
authors.lastname: Baldridge
authors.forename: Balwantray C
authors.initials: BC
authors.lastname: Chauhan
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism / Q000473:pathology*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D049109:Cell Proliferation / Q000187:drug effects*; D002469:Cell Separation; D065130:Endothelin A Receptor Antagonists; D065131:Endothelin B Receptor Antagonists; D019332:Endothelin-1 / Q000494:pharmacology*; D019084:Fluorescent Antibody Technique, Indirect; D016257:Fura-2 / Q000378:metabolism; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D018613:Microscopy, Confocal; D009898:Optic Disk / Q000378:metabolism / Q000473:pathology*; D051381:Rats; D011921:Rats, Inbred WKY; D055647:Rats, Transgenic; D044022:Receptor, Endothelin A / Q000378:metabolism; D044023:Receptor, Endothelin B / Q000172:deficiency* / Q000378:metabolism
chemical_list: D065130:Endothelin A Receptor Antagonists; D065131:Endothelin B Receptor Antagonists; D019332:Endothelin-1; D005904:Glial Fibrillary Acidic Protein; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D002118:Calcium; D016257:Fura-2