Functional characterization of muscarinic receptor subtypes in human duodenal secretion.
OBJECTIVE
Acetylcholine (ACh) stimulates ion secretion in the small intestine and colon. The purpose of the present study was to characterize the ACh-induced electrogenic ion transport in human duodenum and determine the muscarinic receptor subtypes functionally involved.


METHODS
Biopsies from the second part of duodenum were obtained from 28 patients during endoscopy. Biopsies were mounted in modified Ussing chambers with air-suction for measurements of short-circuit current by a previously validated technique. Short-circuit current was measured after application of chloride/bicarbonate transport inhibitors bumetanide, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), diphenylamine-2-carboxylate (DPC), and acetazolamide. 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) and two mamba toxins MT3 and MT7 were used to characterize the mAChR receptor subtypes involved. The effects of transport inhibitors and receptor antagonists were measured by comparing two consecutive responses of ACh on short-circuit current in the same biopsy specimen.


RESULTS
Bumetanide and 4-DAMP significantly inhibited ACh-induced short-circuit current, whereas SITS, DPC, acetazolamide, mamba toxin MT3, and mamba toxin MT7 all failed to show any significant effect.


CONCLUSIONS
In conclusion, our results indicate that muscarinic receptor subtype M3 acts as the main mediator of bumetanide-sensitive ACh-induced secretion in human duodenum.
Department of Medicine M, Division of Gastroenterology, University Hospital of Glostrup, Glostrup, Denmark.
R
R
Larsen
M B
MB
Hansen
N
N
Bindslev
A
A
Mertz-Nielsen
D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000109:Acetylcholine / Q000378:metabolism; D002034:Bumetanide / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology; D004386:Duodenum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D004546:Elapid Venoms / Q000494:pharmacology; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009498:Neurotoxins / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000032:analysis*; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D002121:Calcium Channel Blockers; D004232:Diuretics; D004546:Elapid Venoms; D036341:Intercellular Signaling Peptides and Proteins; D018727:Muscarinic Antagonists; D009498:Neurotoxins; D010455:Peptides; D010880:Piperidines; D011976:Receptors, Muscarinic; C089528:muscarinic toxin 3; C419876:muscarinic toxin 7; D062367:ortho-Aminobenzoates; D002034:Bumetanide; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; C001209:fenamic acid; D000109:Acetylcholine; D000086:Acetazolamide