Cholinergic neuromuscular transmission mediated byinterstitialcellsofCajal inthemyentericlayerinmouseileal longitudinal smooth muscles

To elucidate the roles played by the interstitial cells of Cajal in the myenteric layer (ICC-MY) in cholinergic neuromuscular transmission, we recorded mechanical and electrical activities in response to electrical field stimulation (EFS) of the ileal longitudinal muscle strips from WBB6F1- W/W V (W/W V ) mutant mice, that lacked ICC-MYand com- pared with those in WBB6F1-+/+ (+/+) control mice. In +/+ muscle strips, EFS induced phasic contractions, which were abolished or strongly attenuated by atropine or tetrodotoxin. In W/W V preparations, EFS induced similar phasic contrac- tions, but the cholinergic component was smaller than that in +/+ strips. This was despite of the fact that the contractions because of exogenous applications of carbachol and high K + solution in W/W V strips were comparable to or rather greater than those in the +/+ preparations. EFS induced atropine- sensitive excitatory junction potentials (EJPs) in the +/+ lon- gitudinal smooth muscle cells but not in W/W V cells. In the presence of eserine, EFS induced atropine-sensitive EJPs in W/W V cells. These results suggest that ICC-MY mediate the