title: Mucosal serotonin overflow is associated with colonic stretch rather than phasic contractions.
abstract: Many studies have shown that mucosal serotonin (5-HT) is associated with motility, however, recently there have been some questions to the precise role of this transmitter. The majority of studies have focused on understanding the role of mucosal 5-HT on colonic migratory motor complexes, but very few studies have been carried out to understand how 5-HT release may be associated with other motility patterns.
  
  
  
  Using distal colon segments from C57BL/6J mice, mucosal 5-HT overflow was monitored using amperometry while applying tension in longitudinal or circular directions to stretch the tissue.
  
  
  
  Phasic and basal 5-HT levels were not associated with the strength of phasic contractions, while being altered using scopolamine and L-NNA. There was a significant increase in mucosal 5-HT with longitudinal and circular muscle stretch. A greater applied force was needed to activate 5-HT release in the circular muscle. In the longitudinal muscle, 5-HT levels increased with stretch until 3 mN, after which the levels returned back to baseline. This stretch-evoked 5-HT overflow was inhibited by transient receptor potential A1 (TRPA1) agonist, 30 μM ruthenium red in both circular and longitudinal muscle preparations. The decreased 5-HT overflow after 3 mN of tension was reversed using a 5-HT4 antagonist 100 nM GR113808.
  
  
  
  Our findings show a relationship between colonic stretch and mucosal 5-HT overflow, while no relationship is observed with phasic colonic contractions. Such findings provide more insight into the role of mucosal 5-HT in influencing the pattern of colonic motility to diversify fecal propulsion.
authors.affiliation: School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, UK.
authors.forename: B A
authors.initials: BA
authors.lastname: Patel
mesh_terms: D000818:Animals; D003106:Colon / Q000378:metabolism*; D005769:Gastrointestinal Motility / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*
chemical_list: D012701:Serotonin
keywords: TRPA1; contraction; enterochromaffin cell; mechanosensitivity; serotonin