title: Differences in time to peak carbachol-induced contractions between circular and longitudinal smooth muscles of mouse ileum.
abstract: The muscular layer in the GI tract consists of an inner circular muscular layer and an outer longitudinal muscular layer. Acetylcholine (ACh) is the representative neurotransmitter that causes contractions in the gastrointestinal tracts of most animal species. There are many reports of muscarinic receptor-mediated contraction of longitudinal muscles, but few studies discuss circular muscles. The present study detailed the contractile response in the circular smooth muscles of the mouse ileum. We used small muscle strips (0.2 mm × 1 mm) and large muscle strips (4 × 4 mm) isolated from the circular and longitudinal muscle layers of the mouse ileum to compare contraction responses in circular and longitudinal smooth muscles. The time to peak contractile responses to carbamylcholine (CCh) were later in the small muscle strips (0.2 × 1 mm) of circular muscle (5.7 min) than longitudinal muscles (0.4 min). The time to peak contractile responses to CCh in the large muscle strips (4 × 4 mm) were also later in the circular muscle (3.1 min) than the longitudinal muscle (1.4 min). Furthermore, a muscarinic M2 receptor antagonist and gap junction inhibitor significantly delayed the time to peak contraction of the large muscle strips (4 × 4 mm) from the circular muscular layer. Our findings indicate that muscarinic M2 receptors in the circular muscular layer of mouse ileum exert a previously undocumented function in gut motility via the regulation of gap junctions.
authors.forename: Yasu-Taka
authors.initials: YT
authors.lastname: Azuma
authors.forename: Nanako
authors.initials: N
authors.lastname: Samezawa
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Nishiyama
authors.forename: Hidemitsu
authors.initials: H
authors.lastname: Nakajima
authors.forename: Tadayoshi
authors.initials: T
authors.lastname: Takeuchi
mesh_terms: D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D018679:Cholinergic Agonists / Q000494:pharmacology*; D017629:Gap Junctions / Q000502:physiology; D007082:Ileum / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008810:Mice, Inbred C57BL; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D043585:Receptor, Muscarinic M2 / Q000502:physiology*
chemical_list: D018679:Cholinergic Agonists; D043585:Receptor, Muscarinic M2; D002217:Carbachol