Roles of M2 and M3 muscarinic receptors in cholinergic nerve-induced contractions in mouse ileum studied with receptor knockout mice.
OBJECTIVE
The functional roles of M(2) and M(3) muscarinic receptors in neurogenic cholinergic contractions in gastrointestinal tracts remain to be elucidated. To address this issue, we studied cholinergic nerve-induced contractions in the ileum using mutant mice lacking M(2) or M(3) receptor subtypes.


METHODS
Contractile responses to transmural electrical (TE) stimulation were isometrically recorded in ileal segments from M(2)-knockout (KO), M(3)-KO, M(2)/M(3)-double KO, and wild-type mice.


RESULTS
TE stimulation at 2-50 Hz frequency-dependently evoked a fast, brief contraction followed by a slower, longer one in wild-type, M(2)-KO or M(3)-KO mouse preparations. Tetrodotoxin blocked both the initial and later contractions, while atropine only inhibited the initial contractions. The initial cholinergic contractions were significantly greater in wild-type than M(2)-KO or M(3)-KO mice; the respective mean amplitudes at 50 Hz were 91, 74 and 68 % of 70mM K(+)-induced contraction. Pretreatment with pertussis toxin blocked the cholinergic contractions in M(3)-KO but not in M(2)-KO mice. Cholinergic contractions also remained in wild-type preparations, but their sizes were reduced by 20-30 % at 10-50 Hz. In M(2)/M(3)-double KO mice, TE stimulation evoked only slow, noncholinergic contractions, which were significantly greater in sizes than in any of the other three mouse strains.


CONCLUSIONS
These results demonstrate that M(2) and M(3) receptors participate in mediating cholinergic contractions in mouse ileum with the latter receptors assuming a greater role. Our data also suggest that the lack of both M(2) and M(3) receptors causes upregulation of noncholinergic excitatory innervation of the gut smooth muscle.
Unno
T
T
Laboratory of Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Science, Gifu University, Gifu, Japan.
Matsuyama
H
H
Izumi
Y
Y
Yamada
M
M
Wess
J
J
Komori
S
S
D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002211:Capsaicin / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D007082:Ileum / Q000187:drug effects; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D037342:Pertussis Toxin / Q000494:pharmacology; D043585:Receptor, Muscarinic M2 / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D043587:Receptor, Muscarinic M3 / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D000779:Anesthetics, Local; D018727:Muscarinic Antagonists; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D013779:Tetrodotoxin; D001285:Atropine; D037342:Pertussis Toxin; D002211:Capsaicin