Cholinergic receptors mediating secretion in guinea pig colon

Area of Science:

• Gastroenterology
• Neuroscience
• Pharmacology

Background:

• The enteric nervous system (ENS) regulates colonic function, including ion transport.
• Cholinergic signaling plays a critical role in mediating ENS-evoked responses.
• Understanding receptor involvement is key to deciphering colonic secretory mechanisms.

Purpose of the Study:

• To investigate the role of cholinergic receptors in mediating chloride secretion in the guinea pig distal colon.
• To elucidate the specific types and locations of cholinergic receptors involved in neural stimulation.

Main Methods:

• Utilized muscle-stripped segments of guinea pig distal colon in Ussing chambers.
• Measured short-circuit current (SCC) to assess chloride secretion.
• Administered various pharmacological agents, including tetrodotoxin, hexamethonium, and muscarinic antagonists (atropine, 4-diphenyl acetoxy-N-methylpiperidine, pirenzepine).
• Assessed receptor binding using [3H]quinuclidinyl benzilate.

Main Results:

• Neurally evoked chloride secretion was reduced by muscarinic antagonists, indicating a role for muscarinic receptors.
• Nicotinic stimulation (1,1-Dimethyl-4-phenyl-piperazinium iodide) increased basal SCC.
• Carbachol and bethanechol increased SCC in a concentration-dependent manner, sensitive to tetrodotoxin and hexamethonium.
• Receptor binding studies revealed a potency order for muscarinic antagonists.

Conclusions:

• Cholinergic and noncholinergic pathways significantly regulate chloride transport in the guinea pig distal colon.
• Both nicotinic and muscarinic receptors on enteric neurons projecting to the mucosa are involved.
• Epithelial muscarinic receptors also mediate the chloride secretory response.