Inhibition by beta-CCM of cholecystokinin-induced release of acetylcholine from the longitudinal muscle-myenteric plexus preparation in the guinea-pig ileum.

The antagonism between cholecystokinin (CCK) and methyl beta-carboline-3-carboxylate (beta-CCM) in the nervous system was studied by measuring the release of acetylcholine (ACh) from the longitudinal muscle-myenteric plexus preparation of guinea-pig. The ACh release was assessed by measuring [3H] output from the preparation preincubated with [3H] choline. Thirty mM of KCl caused a pronounced release of [3H] ACh from the preparation. Sulfated cholecystokinin octapeptide (CCK8) also increased the release of [3H] ACh in a dose-dependent manner at concentrations ranging from 10(-10)M to 10(-8)M. CCK8 at a concentration of 10(-8)M released [3H] ACh by about 300% of the 30 mM KCl-induced [3H] ACh release. In the presence of beta-CCM (10(-8)M to 10(-4)M), the release of [3H] ACh by KCl was not affected, but that by CCK8 was significantly inhibited depending on the concentrations of beta-CCM. These results show that the action of CCK8 to stimulate neurons in the myenteric plexus can be selectively antagonized by beta-CCM.