Real-time measurement of serotonin release and motility in guinea pig ileum.
Enterochromaffin (EC) cells are sensors that detect chemical or mechanical stimuli and respond with release of serotonin (5-HT). 5-HT activates local motor reflexes, but whether local motor reflexes also evoke 5-HT release is unknown. The aim of the present study was to establish the relationship between the release of 5-HT and the enteric neural circuits controlling the movements of the intestine. Recordings were made from full-thickness preparations of guinea pig ileum using electrochemical techniques with carbon fibre electrodes to measure local concentrations of 5-HT. The tension in the circular muscle (CM) and longitudinal muscle (LM) was recorded with force transducers. The release of 5-HT from the EC cells was detected selectively and the timing of the events quantified. Pressure-evoked peristalsis caused detectable 5-HT release only when the recording site was invaded by a ring of CM contraction. Spontaneous and stretch-evoked reflex contraction of the CM and LM occurred simultaneously with 5-HT release. Paralysis of the smooth muscle significantly reduced the stretch-evoked release. Muscarinic agonists evoked reflexes that were associated with increases in tension in CM and LM simultaneous with 5-HT release. Tetrodotoxin abolished the coordination between the CM contraction and 5-HT release but not the direct activation of the CM and EC cells by the agonists. In conclusion, the correlation between local motor reflexes and 5-HT release observed in the present study is caused primarily by the contraction of the smooth muscle and subsequent deformation of the mucosa. The EC cell is, thus, a site of convergence for mechanical forces that contribute to the release of 5-HT during motor reflexes.
Bertrand
Paul P
PP
Department of Physiology and Cell Biology, University of Nevada, School of Medicine, Reno, NV 89557, USA. p.bertrand@gmail.com
D000109:Acetylcholine / Q000494:pharmacology; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D004558:Electric Stimulation; D004563:Electrochemistry; D017615:Enteric Nervous System / Q000187:drug effects / Q000502:physiology*; D004759:Enterochromaffin Cells / Q000187:drug effects / Q000378:metabolism*; D005769:Gastrointestinal Motility / Q000187:drug effects; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008564:Membrane Potentials; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000294:innervation; D009466:Neuromuscular Blocking Agents / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D010208:Papaverine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010528:Peristalsis; D012026:Reflex, Stretch / Q000187:drug effects; D012701:Serotonin / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
D000779:Anesthetics, Local; D009466:Neuromuscular Blocking Agents; D009599:Nitroprusside; D012701:Serotonin; D013779:Tetrodotoxin; D001285:Atropine; D010208:Papaverine; D007545:Isoproterenol; D000109:Acetylcholine