Pharmacological difference in muscarinic receptors between circular and longitudinal muscle cells of murine small intestine

In order to estimate exactly changes in the murine peristaltic movement by acetylcholine (ACh), we detected the circular muscle activity in the murine small intestine by measuring the changes in intraluminal pressure of the duodenal segment in vitro. When ACh was applied into the tissue baths, the basal tone of the duodenal preparation along the longitudinal axis increased, whereas the intraluminal pressure that reflected circular muscle activity decreased in a dose-dependent manner. Thus, the circular muscle layer of the murine duodenum relaxed by ACh. The circular relaxations by ACh were also observed in the other parts (jejunum and ileum) of the murine small intestine. The ACh-induced fall in the intraluminal pressure of the murine duodenal preparation was antagonized by atropine (10−6 M), not tetrodotoxin (10−6 M). The results indicate ACh acts as not only the excitatory transmitter for the longitudinal muscle but also the inhibitory transmitter for the circular muscle, and suggest that the functional receptors to ACh are different between longitudinal and circular muscle cells in the murine small intestine. [Copyright &y& Elsevier]