Neuromuscular pharmacology of the anterior intestine of Chaetopterus variopedatus, a filter-feeding polychaete.
The motricity of the anterior intestine of Chaetopterus variopedatus was investigated using extracellular electrodes, force displacement transduction and a pharmacological approach. Rhythmic bursts of impulses were associated with peristaltic waves; the latter were not abolished by removal of the ventral nerve cord which caused a drop in tonus. Acetylcholine induced a contracture and an increase in the frequency of peristaltic waves; these effects were potentiated by eserine and reduced by atropine. Similar responses to adrenaline and noradrenaline were antagonized by propranolol and phentolamine in partially different manners. Gamma-aminobutyric acid (GABA) induced large, picrotoxin-sensitive contractures but failed to change the rate of peristalsis. Serotonin (5-HT) produced a short-term increase in the rate of peristalsis as well as a slight contracture, and a long-term inhibition of peristalsis, all actions antagonized by methysergide. The response to GABA was reduced or abolished during the inhibitory phase of the 5-HT effect. A tetrapeptide related to cholecystokinin/gastrin induced contractures and accelerated peristalsis at a concentration as low as 2.5 X 10(-13) M. It is concluded that multiple neurotransmitter pathways may modulate gut motricity by acting on the peristalsis pacemaker as well as on neuromuscular transmission mechanisms.
D000818:Animals; D002766:Cholecystokinin / Q000502:physiology; D004558:Electric Stimulation; D004594:Electrophysiology; D005755:Gastrins / Q000502:physiology; D005769:Gastrointestinal Motility / Q000187:drug effects; D007422:Intestines / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D009469:Neuromuscular Junction / Q000187:drug effects*; D018377:Neurotransmitter Agents / Q000502:physiology; D010277:Parasympathomimetics / Q000494:pharmacology; D011077:Polychaeta / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D013566:Sympathomimetics / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D005755:Gastrins; D018377:Neurotransmitter Agents; D010277:Parasympathomimetics; D013566:Sympathomimetics; D012701:Serotonin; D005680:gamma-Aminobutyric Acid; D002766:Cholecystokinin