Localization of muscarinic receptors M1R, M2R and M3R in the human colon.
BACKGROUND
Muscarinic acetylcholine receptors (MR) are involved in multiple intestinal reflexes. The cellular localization of subtypes of MRs within enteric circuits mediating muscle and mucosal reflexes remains to be demonstrated. This study aimed to localize the three functionally significant subtypes of MRs in human colon.


METHODS
Reverse transcriptase-PCR was used to determine expression levels of muscarinic receptor subtype (MRs) M1Rs, M2Rs and M3Rs in human colon. Indirect immunofluorescence and confocal microscopy was used to localize MRs in cryostat-cut sections of human colon. Sections were double labeled for multiple cellular and neurochemical markers. Western blotting was used to confirm specificity of the muscarinic antisera used.


RESULTS
All three MR subtypes were expressed in human colon. Immunoreactivity (IR) for M2Rs and M3Rs was most abundant in circular and longitudinal muscle. M1R-IR was most abundant on myenteric and submucosal nerve cells, both cholinergic and nitrergic. M3R-IR was also present on populations on myenteric nerve cell bodies. Immunoreactivity for all three receptors was present on nerve fibers in the circular muscle.


CONCLUSIONS
In the human colon, subtypes of MRs were present on multiple cell types within the enteric circuits underlying motility, secretory and vasoactive reflexes. The cellular distribution for MRs found in this study agrees with data from functional studies, providing insight into the role MRs have in mediating enteric cholinergic neurotransmission.
F. Douglas Stephens Surgical Research Laboratory, Murdoch Children's Research Institute, Parkville, Australia.
A M
AM
Harrington
C J
CJ
Peck
L
L
Liu
E
E
Burcher
J M
JM
Hutson
B R
BR
Southwell
D000293:Adolescent; D015153:Blotting, Western; D002648:Child; D002675:Child, Preschool; D003106:Colon / Q000378:metabolism*; D017615:Enteric Nervous System / Q000378:metabolism; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D018613:Microscopy, Confocal; D009130:Muscle, Smooth / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D043643:Receptor, Muscarinic M1 / Q000235:genetics / Q000378:metabolism*; D043585:Receptor, Muscarinic M2 / Q000235:genetics / Q000378:metabolism*; D043587:Receptor, Muscarinic M3 / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D043643:Receptor, Muscarinic M1; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3