Effects of Ca2+ blockers on the various types of stimuli-induced acetylcholine release from guinea pig ileum myenteric plexus

In the present study, we investigated the effects of various Ca2+ blockers on the release of acetylcholine (ACh) induced by nicotine, electrical field stimulation (EFS) and high-K+. Cd2+ markedly depressed the ACh release due to these stimuli. Verapamil inhibited the nicotine-induced ACh release remarkably and the EFS- or the high-K(+)-induced ACh release to a lesser extent. Since the nicotine- and the EFS-induced ACh releases were inhibited by procaine, the local anesthetic property of verapamil likely contributes in part to the inhibition. Diltiazem abolished the nicotine-induced ACh release completely but did not affect the EFS-induced release and significantly increased the high-K(+)-induced ACh release. These results suggest the absolute requirement for extracellular Ca2+ in the release of ACh induced by nicotine as well as EFS and high-K+. In addition, these stimuli may open the same Ca2+ channel to evoke ACh release.