Z-338 facilitates acetylcholine release from enteric neurons due to blockade of muscarinic autoreceptors in guinea pig stomach.

The mechanism by which Z-338, a novel gastroprokinetic agent, stimulates gastric motility was studied in relation to muscarinic receptors in the guinea pig. Z-338 (3-30 microM) enhanced electrically stimulated contractions and the release of acetylcholine (ACh) that was tetrodotoxin sensitive and extracellular Ca(2+) dependent, in gastric strips. Membrane-binding assay revealed that Z-338 possessed binding affinity for muscarinic M(1) and M(2), but not M(3) receptors. In Xenopus oocytes expressing M(1) and M(2) muscarinic receptors, Z-338 did not produce any response, but inhibited ACh-induced outward currents, thereby indicating that Z-338 acts on the M(1) and M(2) muscarinic receptors as an antagonist. The M(1) receptor antagonist pirenzepine (0.5 microM) and M(2) receptor antagonist AF-DX 116 (1 microM) also enhanced electrically stimulated release of ACh. These results indicate that Z-338 facilitates ACh release from cholinergic nerve terminals by blocking muscarinic M(1) and M(2) autoreceptors, which regulate the release of ACh.