title: Long-term exposure to muscarinic agonists decreases expression of contractile proteins and responsiveness of rabbit tracheal smooth muscle cells.
abstract: BACKGROUND
  Chronic airway diseases, like asthma or COPD, are characterized by excessive acetylcholine release and airway remodeling. The aim of this study was to investigate the long-term effect of muscarinic agonists on the phenotype and proliferation of rabbit tracheal airway smooth muscle cells (ASMCs).
  
  
  METHODS
  ASMCs were serum starved before treatment with muscarinic agonists. Cell phenotype was studied by optical microscopy and indirect immunofluorescence, using smooth muscle α-actin, desmin and SM-Myosin Heavy Chain (SM-MHC) antibodies. [N-methyl-3H]scopolamine binding studies were performed in order to assess M3 muscarinic receptor expression on isolated cell membranes. Contractility studies were performed on isolated ASMCs treated with muscarinic agonists. Proliferation was estimated using methyl-[3H]thymidine incorporation, MTT or cell counting methods. Involvement of PI3K and MAPK signalling pathways was studied by cell incubation with the pathway inhibitors LY294002 and PD98059 respectively.
  
  
  RESULTS
  Prolonged culture of ASMCs with acetylcholine, carbachol or FBS, reduced the expression of α-actin, desmin and SM-MHC compared to cells cultured in serum free medium. Treatment of ASMCs with muscarinic agonists for 3-15 days decreased muscarinic receptor expression and their responsiveness to muscarinic stimulation. Acetylcholine and carbachol induced DNA synthesis and increased cell number, of ASMCs that had acquired a contractile phenotype by 7 day serum starvation. This effect was mediated via a PI3K and MAPK dependent mechanism.
  
  
  CONCLUSIONS
  Prolonged exposure of rabbit ASMCs to muscarinic agonists decreases the expression of smooth muscle specific marker proteins, down-regulates muscarinic receptors and decreases ASMC contractile responsiveness. Muscarinic agonists are mitogenic, via the PI3K and MAPK signalling pathways.
authors.forename: Rodopi
authors.initials: R
authors.lastname: Stamatiou
authors.forename: Efrosini
authors.initials: E
authors.lastname: Paraskeva
authors.forename: Anna
authors.initials: A
authors.lastname: Vasilaki
authors.forename: Ilias
authors.initials: I
authors.lastname: Mylonis
authors.forename: Paschalis Adam
authors.initials: PA
authors.lastname: Molyvdas
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Gourgoulianis
authors.affiliation: Laboratory of Physiology, Department of Medicine, School of Health Sciences, University of Thessaly, 3 Panepistimiou Str, 41500 BIOPOLIS Larissa, Greece. axatzi@med.uth.gr.
authors.forename: Apostolia
authors.initials: A
authors.lastname: Hatziefthimiou
mesh_terms: D000109:Acetylcholine / Q000008:administration & dosage* / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000008:administration & dosage* / Q000494:pharmacology; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003285:Contractile Proteins / Q000096:biosynthesis* / Q000187:drug effects*; D018721:Muscarinic Agonists / Q000008:administration & dosage* / Q000494:pharmacology; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000502:physiology*; D011817:Rabbits; D013997:Time Factors; D014132:Trachea / Q000166:cytology*
chemical_list: D003285:Contractile Proteins; D018721:Muscarinic Agonists; D002217:Carbachol; D000109:Acetylcholine