Volume 56 (2006) Issue: 2006 No#5-6

Excitatory muscarinic M1 receptors mediate in the regulation of guineapig terminal ileum motility

Author(s): Šćepanović Ljiljana, Kojić Zvezdana, Suzić Slavica, Nešić D, Popović Dejana, Mazić Sanja, Ilić S

Keywords:cholinergic receptors, terminal ileum, prejunctional receptors, smooth muscle

In vitro experiments were performed on smooth muscle strips cut out longitudinally or circularly from the terminal ileum about 5 cm from the ileo-coecal sphincter. The aim of this study was to determine the functional role of M1 muscarinic receptor subtype in the regulation of cholinergic contractions of the guinea-pig terminal ileum. Electrical field stimulation (EFS; 16 Hz) produced in vitro contractile responses of the guinea-pig terminal ileum muscle strips (longitudinal and circular muscle layer). Those contractions were inhibited by 1
M tetrodotoxin (2±2% of the control response) and 1
M atropine (1±1% of the control response), thus indicating the activation of intrinsic cholinergic nerves. Exogenous ACh (1
M) induced contractions that were inhibited by 1
M atropine, but not by 1
M tetrodotoxin, indicating a direct effect on the smooth muscle. MCN-343, specific agonist of M1 receptor subtype (5
M) induced contractions that were inhibited by 1
M atropine and by 1
M tetrodotoxin. M1 receptor antagonist pirenzepine (10 nM) had no effect on ACh – induced contractions, but reduced EFS – induced contractions by 11±3% and MCN-A-343 induced contractions by 17±4%. In conclusion, specific M1 receptors modulate terminal ileum contractions by regulating the release of ACh from cholinergic nerves. M1 receptors, present on c